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Title: The Variation of Animals and Plants Under Domestication,
Volume II (of 2)

Author: Charles Darwin

Release date: May 20, 2009 [eBook #28897]

Language: English

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*** START OF THE PROJECT GUTENBERG EBOOK THE
VARIATION OF ANIMALS AND PLANTS UNDER DOMESTICATION,
VOLUME II (OF 2) ***

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and the Project Gutenberg Online Distributed Proofreading Team

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marked passage.

THE VARIATION
OF

ANIMALS AND PLANTS

UNDER DOMESTICATION.
By CHARLES DARWIN, M.A., F.R.S., &c.

IN TWO VOLUMES.—Vol. II.

WITH ILLUSTRATIONS.

LONDON:

JOHN MURRAY, ALBEMARLE STREET.

1868.

The right of Translation is reserved.

LONDON: PRINTED BY WILLIAM CLOWES AND SONS, STAMFORD STREET, AND
CHARING CROSS.

CONTENTS OF VOLUME II.
CHAPTER XII.

INHERITANCE.
WONDERFUL NATURE OF INHERITANCE—PEDIGREES OF OUR DOMESTICATED
ANIMALS—INHERITANCE NOT DUE TO CHANCE—TRIFLING CHARACTERS
INHERITED—DISEASES INHERITED—PECULIARITIES IN THE EYE INHERITED—
DISEASES IN THE HORSE—LONGEVITY AND VIGOUR—ASYMMETRICAL
DEVIATIONS OF STRUCTURE—POLYDACTYLISM AND REGROWTH OF
SUPERNUMERARY DIGITS AFTER AMPUTATION—CASES OF SEVERAL CHILDREN
SIMILARLY AFFECTED FROM NON-AFFECTED PARENTS—WEAK AND FLUCTUATING
INHERITANCE: IN WEEPING TREES, IN DWARFNESS, COLOUR OF FRUIT AND
FLOWERS, COLOUR OF HORSES—NON-INHERITANCE IN CERTAIN CASES—
INHERITANCE OF STRUCTURE AND HABITS OVERBORNE BY HOSTILE CONDITIONS
OF LIFE, BY INCESSANTLY RECURRING VARIABILITY, AND BY REVERSION—
CONCLUSION ... Page 1

CHAPTER XIII.

INHERITANCE continued—REVERSION OR ATAVISM.
DIFFERENT FORMS OF REVERSION—IN PURE OR UNCROSSED BREEDS, AS IN
PIGEONS, FOWLS, HORNLESS CATTLE AND SHEEP, IN CULTIVATED PLANTS—
REVERSION IN FERAL ANIMALS AND PLANTS—REVERSION IN CROSSED VARIETIES
AND SPECIES—REVERSION THROUGH BUD-PROPAGATION, AND BY SEGMENTS IN
THE SAME FLOWER OR FRUIT—IN DIFFERENT PARTS OF THE BODY IN THE SAME
ANIMAL—THE ACT OF CROSSING A DIRECT CAUSE OF REVERSION, VARIOUS CASES
OF, WITH INSTINCTS—OTHER PROXIMATE CAUSES OF REVERSION—LATENT
CHARACTERS—SECONDARY SEXUAL CHARACTERS—UNEQUAL DEVELOPMENT OF
THE TWO SIDES OF THE BODY—APPEARANCE WITH ADVANCING AGE OF
CHARACTERS DERIVED FROM A CROSS—THE GERM WITH ALL ITS LATENT
CHARACTERS A WONDERFUL OBJECT—MONSTROSITIES—PELORIC FLOWERS DUE
IN SOME CASES TO REVERSION ... Page 28

CHAPTER XIV.

INHERITANCE continued—FIXEDNESS OF CHARACTER—
PREPOTENCY—SEXUAL LIMITATION—CORRESPONDENCE OF
AGE.
FIXEDNESS OF CHARACTER APPARENTLY NOT DUE TO ANTIQUITY OF INHERITANCE
—PREPOTENCY OF TRANSMISSION IN INDIVIDUALS OF THE SAME FAMILY, IN
CROSSED BREEDS AND SPECIES; OFTEN STRONGER IN ONE SEX THAN THE OTHER;
SOMETIMES DUE TO THE SAME CHARACTER BEING PRESENT AND VISIBLE IN ONE
BREED AND LATENT IN THE OTHER—INHERITANCE AS LIMITED BY SEX—NEWLY-
ACQUIRED CHARACTERS IN OUR DOMESTICATED ANIMALS OFTEN TRANSMITTED
BY ONE SEX ALONE, SOMETIMES LOST BY ONE SEX ALONE—INHERITANCE AT
CORRESPONDING PERIODS OF LIFE—THE IMPORTANCE OF THE PRINCIPLE WITH
RESPECT TO EMBRYOLOGY; AS EXHIBITED IN DOMESTICATED ANIMALS; AS
EXHIBITED IN THE APPEARANCE AND DISAPPEARANCE OF INHERITED DISEASES;
SOMETIMES SUPERVENING EARLIER IN THE CHILD THAN IN THE PARENT—
SUMMARY OF THE THREE PRECEDING CHAPTERS ... Page 62

CHAPTER XV.

ON CROSSING.
FREE INTERCROSSING OBLITERATES THE DIFFERENCES BETWEEN ALLIED BREEDS
—WHEN THE NUMBERS OF TWO COMMINGLING BREEDS ARE UNEQUAL, ONE
ABSORBS THE OTHER—THE RATE OF ABSORPTION DETERMINED BY PREPOTENCY
OF TRANSMISSION, BY THE CONDITIONS OF LIFE, AND BY NATURAL SELECTION—
ALL ORGANIC BEINGS OCCASIONALLY INTERCROSS; APPARENT EXCEPTIONS—ON
CERTAIN CHARACTERS INCAPABLE OF FUSION; CHIEFLY OR EXCLUSIVELY THOSE
WHICH HAVE SUDDENLY APPEARED IN THE INDIVIDUAL—ON THE MODIFICATION
OF OLD RACES, AND THE FORMATION OF NEW RACES, BY CROSSING—SOME
CROSSED RACES HAVE BRED TRUE FROM THEIR FIRST PRODUCTION—ON THE
CROSSING OF DISTINCT SPECIES IN RELATION TO THE FORMATION OF DOMESTIC
RACES ... Page 85

CHAPTER XVI.

CAUSES WHICH INTERFERE WITH THE FREE CROSSING OF
VARIETIES—INFLUENCE OF DOMESTICATION ON FERTILITY.
DIFFICULTIES IN JUDGING OF THE FERTILITY OF VARIETIES WHEN CROSSED—
VARIOUS CAUSES WHICH KEEP VARIETIES DISTINCT, AS THE PERIOD OF BREEDING
AND SEXUAL PREFERENCE—VARIETIES OF WHEAT SAID TO BE STERILE WHEN
CROSSED—VARIETIES OF MAIZE, VERBASCUM, HOLLYHOCK, GOURDS, MELONS,
AND TOBACCO, RENDERED IN SOME DEGREE MUTUALLY STERILE—
DOMESTICATION ELIMINATES THE TENDENCY TO STERILITY NATURAL TO SPECIES
WHEN CROSSED—ON THE INCREASED FERTILITY OF UNCROSSED ANIMALS AND
PLANTS FROM DOMESTICATION AND CULTIVATION ... Page 100

CHAPTER XVII.

ON THE GOOD EFFECTS OF CROSSING, AND ON THE EVIL
EFFECTS OF CLOSE INTERBREEDING.
DEFINITION OF CLOSE INTERBREEDING—AUGMENTATION OF MORBID TENDENCIES
—GENERAL EVIDENCE ON THE GOOD EFFECTS DERIVED FROM CROSSING, AND ON
THE EVIL EFFECTS FROM CLOSE INTERBREEDING—CATTLE, CLOSELY INTERBRED;
HALF-WILD CATTLE LONG KEPT IN THE SAME PARKS—SHEEP—FALLOW-DEER—
DOGS—RABBITS—PIGS—MAN, ORIGIN OF HIS ABHORRENCE OF INCESTUOUS
MARRIAGES—FOWLS—PIGEONS—HIVE-BEES—PLANTS, GENERAL
CONSIDERATIONS ON THE BENEFITS DERIVED FROM CROSSING—MELONS, FRUIT-
TREES, PEAS, CABBAGES, WHEAT, AND FOREST-TREES—ON THE INCREASED SIZE OF
HYBRID PLANTS, NOT EXCLUSIVELY DUE TO THEIR STERILITY—ON CERTAIN
PLANTS WHICH EITHER NORMALLY OR ABNORMALLY ARE SELF-IMPOTENT, BUT ARE
FERTILE, BOTH ON THE MALE AND FEMALE SIDE, WHEN CROSSED WITH DISTINCT
INDIVIDUALS EITHER OF THE SAME OR ANOTHER SPECIES—CONCLUSION ... Page
114

CHAPTER XVIII.

ON THE ADVANTAGES AND DISADVANTAGES OF CHANGED
CONDITIONS OF LIFE: STERILITY FROM VARIOUS CAUSES.
ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OF LIFE—
STERILITY FROM CHANGED CONDITIONS, IN ANIMALS, IN THEIR NATIVE COUNTRY

AND IN MENAGERIES—MAMMALS, BIRDS, AND INSECTS—LOSS OF SECONDARY
SEXUAL CHARACTERS AND OF INSTINCTS—CAUSES OF STERILITY—STERILITY OF
DOMESTICATED ANIMALS FROM CHANGED CONDITIONS—SEXUAL
INCOMPATIBILITY OF INDIVIDUAL ANIMALS—STERILITY OF PLANTS FROM
CHANGED CONDITIONS OF LIFE—CONTABESCENCE OF THE ANTHERS—
MONSTROSITIES AS A CAUSE OF STERILITY—DOUBLE FLOWERS—SEEDLESS FRUIT
—STERILITY FROM THE EXCESSIVE DEVELOPMENT OF THE ORGANS OF
VEGETATION—FROM LONG-CONTINUED PROPAGATION BY BUDS—INCIPIENT
STERILITY THE PRIMARY CAUSE OF DOUBLE FLOWERS AND SEEDLESS FRUIT ...
Page 145

CHAPTER XIX.

SUMMARY OF THE FOUR LAST CHAPTERS, WITH REMARKS ON
HYBRIDISM.
ON THE EFFECTS OF CROSSING—THE INFLUENCE OF DOMESTICATION ON FERTILITY
—CLOSE INTERBREEDING—GOOD AND EVIL RESULTS FROM CHANGED
CONDITIONS OF LIFE—VARIETIES WHEN CROSSED NOT INVARIABLY FERTILE—ON
THE DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND VARIETIES—
CONCLUSIONS WITH RESPECT TO HYBRIDISM—LIGHT THROWN ON HYBRIDISM BY
THE ILLEGITIMATE PROGENY OF DIMORPHIC AND TRIMORPHIC PLANTS—STERILITY
OF CROSSED SPECIES DUE TO DIFFERENCES CONFINED TO THE REPRODUCTIVE
SYSTEM—NOT ACCUMULATED THROUGH NATURAL SELECTION—REASONS WHY
DOMESTIC VARIETIES ARE NOT MUTUALLY STERILE—TOO MUCH STRESS HAS BEEN
LAID ON THE DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND CROSSED
VARIETIES—CONCLUSION ... Page 173

CHAPTER XX.

SELECTION BY MAN.
SELECTION A DIFFICULT ART—METHODICAL, UNCONSCIOUS, AND NATURAL
SELECTION—RESULTS OF METHODICAL SELECTION—CARE TAKEN IN SELECTION
—SELECTION WITH PLANTS—SELECTION CARRIED ON BY THE ANCIENTS, AND BY
SEMI-CIVILISED PEOPLE—UNIMPORTANT CHARACTERS OFTEN ATTENDED TO—
UNCONSCIOUS SELECTION—AS CIRCUMSTANCES SLOWLY CHANGE, SO HAVE OUR
DOMESTICATED ANIMALS CHANGED THROUGH THE ACTION OF UNCONSCIOUS

SELECTION—INFLUENCE OF DIFFERENT BREEDERS ON THE SAME SUB-VARIETY—
PLANTS AS AFFECTED BY UNCONSCIOUS SELECTION—EFFECTS OF SELECTION AS
SHOWN BY THE GREAT AMOUNT OF DIFFERENCE IN THE PARTS MOST VALUED BY
MAN ... Page 192

CHAPTER XXI.

SELECTION—continued.
NATURAL SELECTION AS AFFECTING DOMESTIC PRODUCTIONS—CHARACTERS
WHICH APPEAR OF TRIFLING VALUE OFTEN OF REAL IMPORTANCE—
CIRCUMSTANCES FAVOURABLE TO SELECTION BY MAN—FACILITY IN PREVENTING
CROSSES, AND THE NATURE OF THE CONDITIONS—CLOSE ATTENTION AND
PERSEVERANCE INDISPENSABLE—THE PRODUCTION OF A LARGE NUMBER OF
INDIVIDUALS ESPECIALLY FAVOURABLE—WHEN NO SELECTION IS APPLIED,
DISTINCT RACES ARE NOT FORMED—HIGHLY-BRED ANIMALS LIABLE TO
DEGENERATION—TENDENCY IN MAN TO CARRY THE SELECTION OF EACH
CHARACTER TO AN EXTREME POINT, LEADING TO DIVERGENCE OF CHARACTER,
RARELY TO CONVERGENCE—CHARACTERS CONTINUING TO VARY IN THE SAME
DIRECTION IN WHICH THEY HAVE ALREADY VARIED—DIVERGENCE OF CHARACTER,
WITH THE EXTINCTION OF INTERMEDIATE VARIETIES, LEADS TO DISTINCTNESS IN
OUR DOMESTIC RACES—LIMIT TO THE POWER OF SELECTION—LAPSE OF TIME
IMPORTANT—MANNER IN WHICH DOMESTIC RACES HAVE ORIGINATED—
SUMMARY ... Page 224

CHAPTER XXII.

CAUSES OF VARIABILITY.
VARIABILITY DOES NOT NECESSARILY ACCOMPANY REPRODUCTION—CAUSES
ASSIGNED BY VARIOUS AUTHORS—INDIVIDUAL DIFFERENCES—VARIABILITY OF
EVERY KIND DUE TO CHANGED CONDITIONS OF LIFE—ON THE NATURE OF SUCH
CHANGES—CLIMATE, FOOD, EXCESS OF NUTRIMENT—SLIGHT CHANGES
SUFFICIENT—EFFECTS OF GRAFTING ON THE VARIABILITY OF SEEDLING-TREES—
DOMESTIC PRODUCTIONS BECOME HABITUATED TO CHANGED CONDITIONS—ON
THE ACCUMULATIVE ACTION OF CHANGED CONDITIONS—CLOSE INTERBREEDING
AND THE IMAGINATION OF THE MOTHER SUPPOSED TO CAUSE VARIABILITY—
CROSSING AS A CAUSE OF THE APPEARANCE OF NEW CHARACTERS—VARIABILITY

FROM THE COMMINGLING OF CHARACTERS AND FROM REVERSION—ON THE
MANNER AND PERIOD OF ACTION OF THE CAUSES WHICH EITHER DIRECTLY, OR
INDIRECTLY THROUGH THE REPRODUCTIVE SYSTEM, INDUCE VARIABILITY ... Page
250

CHAPTER XXIII.

DIRECT AND DEFINITE ACTION OF THE EXTERNAL CONDITIONS
OF LIFE.
SLIGHT MODIFICATIONS IN PLANTS FROM THE DEFINITE ACTION OF CHANGED
CONDITIONS, IN SIZE, COLOUR, CHEMICAL PROPERTIES, AND IN THE STATE OF THE
TISSUES—LOCAL DISEASES—CONSPICUOUS MODIFICATIONS FROM CHANGED
CLIMATE OR FOOD, ETC.—PLUMAGE OF BIRDS AFFECTED BY PECULIAR
NUTRIMENT, AND BY THE INOCULATION OF POISON—LAND-SHELLS—
MODIFICATIONS OF ORGANIC BEINGS IN A STATE OF NATURE THROUGH THE
DEFINITE ACTION OF EXTERNAL CONDITIONS—COMPARISON OF AMERICAN AND
EUROPEAN TREES—GALLS—EFFECTS OF PARASITIC FUNGI—CONSIDERATIONS
OPPOSED TO THE BELIEF IN THE POTENT INFLUENCE OF CHANGED EXTERNAL
CONDITIONS—PARALLEL SERIES OF VARIETIES—AMOUNT OF VARIATION DOES
NOT CORRESPOND WITH THE DEGREE OF CHANGE IN THE CONDITIONS—BUD-
VARIATION—MONSTROSITIES PRODUCED BY UNNATURAL TREATMENT—
SUMMARY ... Page 271

CHAPTER XXIV.

LAWS OF VARIATION—USE AND DISUSE, ETC.
NISUS FORMATIVUS, OR THE CO-ORDINATING POWER OF THE ORGANISATION—ON
THE EFFECTS OF THE INCREASED USE AND DISUSE OF ORGANS—CHANGED HABITS
OF LIFE—ACCLIMATISATION WITH ANIMALS AND PLANTS—VARIOUS METHODS BY
WHICH THIS CAN BE EFFECTED—ARRESTS OF DEVELOPMENT—RUDIMENTARY
ORGANS ... Page 293

CHAPTER XXV.

LAWS OF VARIATION, continued—CORRELATED VARIABILITY.

EXPLANATION OF TERM—CORRELATION AS CONNECTED WITH DEVELOPMENT—
MODIFICATIONS CORRELATED WITH THE INCREASED OR DECREASED SIZE OF PARTS
—CORRELATED VARIATION OF HOMOLOGOUS PARTS—FEATHERED FEET IN BIRDS
ASSUMING THE STRUCTURE OF THE WINGS—CORRELATION BETWEEN THE HEAD
AND THE EXTREMITIES—BETWEEN THE SKIN AND DERMAL APPENDAGES—
BETWEEN THE ORGANS OF SIGHT AND HEARING—CORRELATED MODIFICATIONS IN
THE ORGANS OF PLANTS—CORRELATED MONSTROSITIES—CORRELATION
BETWEEN THE SKULL AND EARS—SKULL AND CREST OF FEATHERS—SKULL AND
HORNS—CORRELATION OF GROWTH COMPLICATED BY THE ACCUMULATED
EFFECTS OF NATURAL SELECTION—COLOUR AS CORRELATED WITH
CONSTITUTIONAL PECULIARITIES ... Page 319

CHAPTER XXVI.

LAWS OF VARIATION, continued—SUMMARY.
ON THE AFFINITY AND COHESION OF HOMOLOGOUS PARTS—ON THE VARIABILITY
OF MULTIPLE AND HOMOLOGOUS PARTS—COMPENSATION OF GROWTH—
MECHANICAL PRESSURE—RELATIVE POSITION OF FLOWERS WITH RESPECT TO THE
AXIS OF THE PLANT, AND OF SEEDS IN THE CAPSULE, AS INDUCING VARIATION—
ANALOGOUS OR PARALLEL VARIETIES—SUMMARY OF THE THREE LAST CHAPTERS
... Page 339

CHAPTER XXVII.

PROVISIONAL HYPOTHESIS OF PANGENESIS.
PRELIMINARY REMARKS—FIRST PART:—THE FACTS TO BE CONNECTED UNDER A
SINGLE POINT OF VIEW, NAMELY, THE VARIOUS KINDS OF REPRODUCTION—THE
DIRECT ACTION OF THE MALE ELEMENT ON THE FEMALE—DEVELOPMENT—THE
FUNCTIONAL INDEPENDENCE OF THE ELEMENTS OR UNITS OF THE BODY—
VARIABILITY—INHERITANCE—REVERSION.

SECOND PART:—STATEMENT OF THE HYPOTHESIS—HOW FAR THE NECESSARY
ASSUMPTIONS ARE IMPROBABLE—EXPLANATION BY AID OF THE HYPOTHESIS OF
THE SEVERAL CLASSES OF FACTS SPECIFIED IN THE FIRST PART—CONCLUSION ...
Page 357

CHAPTER XXVIII.

CONCLUDING REMARKS.
DOMESTICATION—NATURE AND CAUSES OF VARIABILITY—SELECTION—
DIVERGENCE AND DISTINCTNESS OF CHARACTER—EXTINCTION OF RACES—
CIRCUMSTANCES FAVOURABLE TO SELECTION BY MAN—ANTIQUITY OF CERTAIN
RACES—THE QUESTION WHETHER EACH PARTICULAR VARIATION HAS BEEN
SPECIALLY PREORDAINED ... Page 405

Index ... Page 433

ERRATA.

Vol. II., pp. 18, 232, 258, for Cratægus oxycantha, read
oxyacantha.
,, p. 98, 8 lines from top, for Dianthus armoria read
armeria.
,, ,, 156, 15 lines from bottom, for Casuarinus read
Casuarius.
,, ,, ,, 4 lines from bottom, for Grus cineria read
cinerea.
,, ,, 168, 11 lines from top, for Œsculus read Æsculus.
,, ,, 300, 3 lines from top, for anastomising read
anastomosing.
,, ,, ,, foot-note, for Birckell read Brickell.

THE

VARIATION OF ANIMALS AND PLANTS
UNDER DOMESTICATION.

CHAPTER XII.

INHERITANCE.

WONDERFUL NATURE OF INHERITANCE—PEDIGREES OF OUR DOMESTICATED
ANIMALS—INHERITANCE NOT DUE TO CHANCE—TRIFLING CHARACTERS
INHERITED—DISEASES INHERITED—PECULIARITIES IN THE EYE INHERITED
—DISEASES IN THE HORSE—LONGEVITY AND VIGOUR—ASYMMETRICAL
DEVIATIONS OF STRUCTURE—POLYDACTYLISM AND REGROWTH OF
SUPERNUMERARY DIGITS AFTER AMPUTATION—CASES OF SEVERAL
CHILDREN SIMILARLY AFFECTED FROM NON-AFFECTED PARENTS—WEAK AND
FLUCTUATING INHERITANCE: IN WEEPING TREES, IN DWARFNESS, COLOUR OF
FRUIT AND FLOWERS, COLOUR OF HORSES—NON-INHERITANCE IN CERTAIN
CASES—INHERITANCE OF STRUCTURE AND HABITS OVERBORNE BY HOSTILE
CONDITIONS OF LIFE, BY INCESSANTLY RECURRING VARIABILITY, AND BY
REVERSION—CONCLUSION.

The subject of inheritance is an immense one, and has been treated by many
authors. One work alone, 'De l'Hérédité Naturelle,' by Dr. Prosper Lucas,
runs to the length of 1562 pages. We must confine ourselves to certain
points which have an important bearing on the general subject of variation,
both with domestic and natural productions. It is obvious that a variation
which is not inherited throws no light on the derivation of species, nor is of
any service to man, except in the case of perennial plants, which can be
propagated by buds.
If animals and plants had never been domesticated, and wild ones alone had
been observed, we should probably never have heard the saying, that "like
begets like." The proposition would have been as self-evident, as that all the

buds on the same tree are alike, though neither proposition is strictly true.
For, as has often been remarked, probably no two individuals are identically
the same. All wild animals recognise each other, which shows that there is
some difference between them; and when the eye is well practised, the
shepherd knows each sheep, and man can distinguish a fellow-man out of
millions on millions of other men. Some authors have gone so far as to
maintain that the production of slight differences is as much a necessary
function of the powers of generation, as the production of offspring like
their parents. This view, as we shall see in a future chapter, is not
theoretically probable, though practically it holds good. The saying that
"like begets like" has in fact arisen from the perfect confidence felt by
breeders, that a superior or inferior animal will generally reproduce its kind;
but this very superiority or inferiority shows that the individual in question
has departed slightly from its type.
The whole subject of inheritance is wonderful. When a new character
arises, whatever its nature may be, it generally tends to be inherited, at least
in a temporary and sometimes in a most persistent manner. What can be
more wonderful than that some trifling peculiarity, not primordially
attached to the species, should be transmitted through the male or female
sexual cells, which are so minute as not to be visible to the naked eye, and
afterwards through the incessant changes of a long course of development,
undergone either in the womb or in the egg, and ultimately appear in the
offspring when mature, or even when quite old, as in the case of certain
diseases? Or again, what can be more wonderful than the well-ascertained
fact that the minute ovule of a good milking cow will produce a male, from
whom a cell, in union with an ovule, will produce a female, and she, when
mature, will have large mammary glands, yielding an abundant supply of
milk, and even milk of a particular quality? Nevertheless, the real subject of
surprise is, as Sir H. Holland has well remarked,[1] not that a character
should be inherited, but that any should ever fail to be inherited. In a future
chapter, devoted to an hypothesis which I have termed pangenesis, an
attempt will be made to show the means by which characters of all kinds
are transmitted from generation to generation.

Some writers,[2] who have not attended to natural history, have attempted to
show that the force of inheritance has been much exaggerated. The breeders
of animals would smile at such simplicity; and if they condescended to

make any answer, might ask what would be the chance of winning a prize if
two inferior animals were paired together? They might ask whether the
half-wild Arabs were led by theoretical notions to keep pedigrees of their
horses? Why have pedigrees been scrupulously kept and published of the
Shorthorn cattle, and more recently of the Hereford breed? Is it an illusion
that these recently improved animals safely transmit their excellent qualities
even when crossed with other breeds? have the Shorthorns, without good
reason, been purchased at immense prices and exported to almost every
quarter of the globe, a thousand guineas having been given for a bull? With
greyhounds pedigrees have likewise been kept, and the names of such dogs,
as Snowball, Major, &c., are as well known to coursers as those of Eclipse
and Herod on the turf. Even with the Gamecock pedigrees of famous strains
were formerly kept, and extended back for a century. With pigs, the
Yorkshire and Cumberland breeders "preserve and print pedigrees;" and to
show how such highly-bred animals are valued, I may mention that Mr.
Brown, who won all the first prizes for small breeds at Birmingham in
1850, sold a young sow and boar of his breed to Lord Ducie for 43 guineas;
the sow alone was afterwards sold to the Rev. F. Thursby for 65 guineas;
who writes, "she paid me very well, having sold her produce for 300l., and
having now four breeding sows from her."[3] Hard cash paid down, over and
over again, is an excellent test of inherited superiority. In fact, the whole art
of breeding, from which such great results have been attained during the
present century, depends on the inheritance of each small detail of structure.
But inheritance is not certain; for if it were, the breeder's art[4] would be
reduced to a certainty, and there would be little scope left for all that skill
and perseverance shown by the men who have left an enduring monument
of their success in the present state of our domesticated animals.
It is hardly possible, within a moderate compass, to impress on the mind of
those who have not attended to the subject, the full conviction of the force
of inheritance which is slowly acquired by rearing animals, by studying the
many treatises which have been published on the various domestic animals,
and by conversing with breeders. I will select a few facts of the kind, which,
as far as I can judge, have most influenced my own mind. With man and the
domestic animals, certain peculiarities have appeared in an individual, at
rare intervals, or only once or twice in the history of the world, but have
reappeared in several of the children and grandchildren. Thus Lambert, "the

porcupine-man," whose skin was thickly covered with warty projections,
which were periodically moulted, had all his six children and two grandsons
similarly affected.[5] The face and body being covered with long hair,
accompanied by deficient teeth (to which I shall hereafter refer), occurred
in three successive generations in a Siamese family; but this case is not
unique, as a woman[6] with a completely hairy face was exhibited in
London in 1663, and another instance has recently occurred. Colonel
Hallam[7] has described a race of two-legged pigs, "the hinder extremities
being entirely wanting;" and this deficiency was transmitted through three
generations. In fact, all races presenting any remarkable peculiarity, such as
solid-hoofed swine, Mauchamp sheep, niata cattle, &c., are instances of the
long-continued inheritance of rare deviations of structure.
When we reflect that certain extraordinary peculiarities have thus appeared
in a single individual out of many millions, all exposed in the same country
to the same general conditions of life, and, again, that the same
extraordinary peculiarity has sometimes appeared in individuals living
under widely different conditions of life, we are driven to conclude that
such peculiarities are not directly due to the action of the surrounding
conditions, but to unknown laws acting on the organisation or constitution
of the individual;—that their production stands in hardly closer relation to
the conditions than does life itself. If this be so, and the occurrence of the
same unusual character in the child and parent cannot be attributed to both
having been exposed to the same unusual conditions, then the following
problem is worth consideration, as showing that the result cannot be due, as
some authors have supposed, to mere coincidence, but must be consequent
on the members of the same family inheriting something in common in
their constitution. Let it be assumed that, in a large population, a particular
affection occurs on an average in one out of a million, so that the à priori
chance that an individual taken at random will be so affected is only one in
a million. Let the population consist of sixty millions, composed, we will
assume, of ten million families, each containing six members. On these
data, Professor Stokes has calculated for me that the odds will be no less
than 8333 millions to 1 that in the ten million families there will not be even
a single family in which one parent and two children will be affected by the
peculiarity in question. But numerous cases could be given, in which
several children have been affected by the same rare peculiarity with one of

their parents; and in this case, more especially if the grandchildren be
included in the calculation, the odds against mere coincidence become
something prodigious, almost beyond enumeration.
In some respects the evidence of inheritance is more striking when we
consider the reappearance of trifling peculiarities. Dr. Hodgkin formerly
told me of an English family in which, for many generations, some
members had a single lock differently coloured from the rest of the hair. I
knew an Irish gentleman, who, on the right side of his head, had a small
white lock in the midst of his dark hair: he assured me that his grandmother
had a similar lock on the same side, and his mother on the opposite side.
But it is superfluous to give instances; every shade of expression, which
may often be seen alike in parents and children, tells the same story. On
what a curious combination of corporeal structure, mental character, and
training, must handwriting depend! yet every one must have noted the
occasional close similarity of the handwriting in father and son, although
the father had not taught his son. A great collector of franks assured me that
in his collection there were several franks of father and son hardly
distinguishable except by their dates. Hofacker, in Germany, remarks on the
inheritance of handwriting; and it has even been asserted that English boys
when taught to write in France naturally cling to their English manner of
writing.[8] Gait, gestures, voice, and general bearing are all inherited, as the
illustrious Hunter and Sir A. Carlisle have insisted.[9] My father
communicated to me two or three striking instances, in one of which a man
died during the early infancy of his son, and my father, who did not see this
son until grown up and out of health, declared that it seemed to him as if his
old friend had risen from the grave, with all his highly peculiar habits and
manners. Peculiar manners pass into tricks, and several instances could be
given of their inheritance; as in the case, often quoted, of the father who
generally slept on his back, with his right leg crossed over the left, and
whose daughter, whilst an infant in the cradle, followed exactly the same
habit, though an attempt was made to cure her.[10] I will give one instance
which has fallen under my own observation, and which is curious from
being a trick associated with a peculiar state of mind, namely, pleasurable
emotion. A boy had the singular habit, when pleased, of rapidly moving his
fingers parallel to each other, and, when much excited, of raising both
hands, with the fingers still moving, to the sides of his face on a level with

the eyes; this boy, when almost an old man, could still hardly resist this
trick when much pleased, but from its absurdity concealed it. He had eight
children. Of these, a girl, when pleased, at the age of four and a half years,
moved her fingers in exactly the same way, and what is still odder, when
much excited, the raised both her hands, with her fingers still moving, to the
sides of her face, in exactly the same manner as her father had done, and
sometimes even still continued to do when alone. I never heard of any one
excepting this one man and his little daughter who had this strange habit;
and certainly imitation was in this instance out of the question.
Some writers have doubted whether those complex mental attributes, on
which genius and talent depend, are inherited, even when both parents are
thus endowed. But he who will read Mr. Galton's able paper[11] on
hereditary talent will have his doubts allayed.
Unfortunately it matters not, as far as inheritance is concerned, how
injurious a quality or structure may be if compatible with life. No one can
read the many treatises[12] on hereditary disease and doubt this. The
ancients were strongly of this opinion, or, as Ranchin expresses it, Omnes
Græci, Arabes, et Latini in eo consentiunt. A long catalogue could be given
of all sorts of inherited malformations and of predisposition to various
diseases. With gout, fifty per cent. of the cases observed in hospital practice
are, according to Dr. Garrod, inherited, and a greater percentage in private
practice. Every one knows how often insanity runs in families, and some of
the cases given by Mr. Sedgwick are awful,—as of a surgeon, whose
brother, father, and four paternal uncles were all insane, the latter dying by
suicide; of a Jew, whose father, mother, and six brothers and sisters were all
mad; and in some other cases several members of the same family, during
three or four successive generations, have committed suicide. Striking
instances have been recorded of epilepsy, consumption, asthma, stone in the
bladder, cancer, profuse bleeding from the slightest injuries, of the mother
not giving milk, and of bad parturition being inherited. In this latter respect
I may mention an odd case given by a good observer,[13] in which the fault
lay in the offspring, and not in the mother: in a part of Yorkshire the farmers
continued to select cattle with large hind-quarters, until they made a strain
called "Dutch-buttocked," and "the monstrous size of the buttocks of the

calf was frequently fatal to the cow, and numbers of cows were annually
lost in calving."

Instead of giving numerous details on various inherited malformations
and diseases, I will confine myself to one organ, that which is the most
complex, delicate, and probably best-known in the human frame,
namely, the eye, with its accessory parts. To begin with the latter: I
have heard of a family in which parents and children were affected by
drooping eyelids, in so peculiar a manner, that they could not see
without throwing their heads backwards; and Sir A. Carlisle[14]
specifies a pendulous fold to the eyelids as inherited. "In a family,"
says Sir H. Holland,[15] "where the father had a singular elongation of
the upper eyelid, seven or eight children were born with the same
deformity; two or three other children having it not." Many persons, as
I year from Mr. Paget, have two or three of the hairs in their eyebrows
(apparently corresponding with the vibrissæ of the lower animals)
much longer than the others; and even so trifling a peculiarity as this
certainly runs in families.
With respect to the eye itself, the highest authority in England, Mr.
Bowman, has been so kind as to give me the following remarks on
certain inherited imperfections. First, hypermetropia, or morbidly long
sight: in this affection, the organ, instead of being spherical, is too flat
from front to back, and is often altogether too small, so that the retina
is brought too forward for the focus of the humours; consequently a
convex glass is required for clear vision of near objects, and frequently
even of distant ones. This state occurs congenitally, or at a very early
age, often in several children of the same family, where one of the
parents has presented it.[16] Secondly, myopia, or short-sight, in which
the eye is egg-shaped, and too long from front to back; the retina in
this case lies behind the focus, and is therefore fitted to see distinctly
only very near objects. This condition is not commonly congenital, but
comes on in youth, the liability to it being well known to be
transmissible from parent to child. The change from the spherical to
the ovoidal shape seems the immediate consequence of something like
inflammation of the coats, under which they yield, and there is ground
for believing that it may often originate in causes acting directly on the

individual affected, and may thenceforward become transmissible.
When both parents are myopic Mr. Bowman has observed the
hereditary tendency in this direction to be heightened, and some of the
children to be myopic at an earlier age or in a higher degree than their
parents. Thirdly, squinting is a familiar example of hereditary
transmission: it is frequently a result of such optical defects as have
been above mentioned; but the more primary and uncomplicated forms
of it are also sometimes in a marked degree transmitted in a family.
Fourthly, Cataract, or opacity of the crystalline lens, is commonly
observed in persons whose parents have been similarly affected, and
often at an earlier age in the children than in the parents. Occasionally
more than one child in a family is thus afflicted, one of whose parents
or other relation presents the senile form of the complaint. When
cataract affects several members of a family in the same generation, it
is often seen to commence at about the same age in each; e.g., in one
family several infants or young persons may suffer from it; in another,
several persons of middle age. Mr. Bowman also informs me that he
has occasionally seen, in several members of the same family, various
defects in either the right or left eye; and Mr. White Cooper has often
seen peculiarities of vision confined to one eye reappearing in the same
eye in the offspring.[17]
The following cases are taken from an able paper by Mr. W. Sedgwick,
and from Dr. Prosper Lucas.[18] Amaurosis, either congenital or
coming on late in life, and causing total blindness, is often inherited; it
has been observed in three successive generations. Congenital absence
of the iris has likewise been transmitted for three generations, a cleft-
iris for four generations, being limited in this latter case to the males of
the family. Opacity of the cornea and congenital smallness of the eyes
have been inherited. Portal records a curious case, in which a father
and two sons were rendered blind, whenever the head was bent
downwards, apparently owing to the crystalline lens, with its capsule,
slipping through an unusually large pupil into the anterior chamber of
the eye. Day-blindness, or imperfect vision under a bright light, is
inherited, as is night-blindness, or an incapacity to see except under a
strong light: a case has been recorded, by M. Cunier, of this latter
defect having affected eighty-five members of the same family during

six generations. The singular incapacity of distinguishing colours,
which has been called Daltonism, is notoriously hereditary, and has
been traced through five generations, in which it was confined to the
female sex.
With respect to the colour of the iris: deficiency of colouring matter is
well known to be hereditary in albinoes. The iris of one eye being of a
different colour from that of the other, and the iris being spotted, are
cases which have been inherited. Mr. Sedgwick gives, in addition, on
the authority of Dr. Osborne,[19] the following curious instance of
strong inheritance: a family of sixteen sons and five daughters all had
eyes "resembling in miniature the markings on the back of a
tortoiseshell cat." The mother of this large family had three sisters and
a brother all similarly marked, and they derived this peculiarity from
their mother, who belonged to a family notorious for transmitting it to
their posterity.
Finally, Dr. Lucas emphatically remarks that there is not one single
faculty of the eye which is not subject to anomalies; and not one which
is not subjected to the principle of inheritance. Mr. Bowman agrees
with the general truth of this proposition; which of course does not
imply that all malformations are necessarily inherited; this would not
even follow if both parents were affected by an anomaly which in most
cases was transmissible.

Even if no single fact had been known with respect to the inheritance of
disease and malformations by man, the evidence would have been ample in
the case of the horse. And this might have been expected, as horses breed
much quicker than man, are matched with care, and are highly valued. I
have consulted many works, and the unanimity of the belief by veterinaries
of all nations in the transmission of various morbid tendencies is surprising.
Authors, who have had wide experience, give in detail many singular cases,
and assert that contracted feet, with the numerous contingent evils, of ring-
bones, curbs, splints, spavin, founder and weakness of the front legs,
roaring or broken and thick wind, melanosis, specific ophthalmia, and
blindness (the great French veterinary Hazard going so far as to say that a
blind race could soon be formed), crib-biting, jibbing, and ill-temper, are all
plainly hereditary. Youatt sums up by saying "there is scarcely a malady to

which the horse is subject which is not hereditary;" and M. Bernard adds
that the doctrine "that there is scarcely a disease which does not run in the
stock, is gaining new advocates every day."[20] So it is in regard to cattle,
with consumption, good and bad teeth, fine skin, &c. &c. But enough, and
more than enough, has been said on disease. Andrew Knight, from his own
experience, asserts that disease is hereditary with plants; and this assertion
is endorsed by Lindley.[21]
Seeing how hereditary evil qualities are, it is fortunate that good health,
vigour, and longevity are equally inherited. It was formerly a well-known
practice, when annuities were purchased to be received during the lifetime
of a nominee, to search out a person belonging to a family of which many
members had lived to extreme old age. As to the inheritance of vigour and
endurance, the English race-horse offers an excellent instance. Eclipse
begot 334, and King Herod 497 winners. A "cock-tail" is a horse not purely
bred, but with only one-eighth or one-sixteenth impure blood in his veins,
yet very few instances have ever occurred of such horses having won a
great race. They are sometimes as fleet for short distances as thoroughbreds,
but as Mr. Robson, the great trainer, asserts, they are deficient in wind, and
cannot keep up the pace. Mr. Lawrence also remarks, "perhaps no instance
has ever occurred of a three-part-bred horse saving his 'distance' in running
two miles with thoroughbred racers." It has been stated by Cecil, that when
unknown horses, whose parents were not celebrated, have unexpectedly
won great races, as in the case of Priam, they can always be proved to be
descended on both sides, through many generations, from first-rate
ancestors. On the Continent, Baron Cameronn challenges, in a German
veterinary periodical, the opponents of the English race-horse, to name one
good horse on the Continent which has not some English race-blood in his
veins.[22]
With respect to the transmission of the many slight, but infinitely
diversified characters, by which the domestic races of animals and plants
are distinguished, nothing need be said; for the very existence of persistent
races proclaims the power of inheritance.
A few special cases, however, deserve some consideration. It might have
been anticipated, that deviations from the law of symmetry would not have
been inherited. But Anderson[23] states that a rabbit produced in a litter a

young animal having only one ear; and from this animal a breed was
formed which steadily produced one-eared rabbits. He also mentions a
bitch, with a single leg deficient, and she produced several puppies with the
same deficiency. From Hofacker's account[24] it appears that a one-horned
stag was seen in 1781 in a forest in Germany, in 1788 two, and afterwards,
from year to year, many were observed with only one horn on the right side
of the head. A cow lost a horn by suppuration,[25] and she produced three
calves which had on the same side of the head, instead of a horn, a small
bony lump attached merely to the skin; but we here approach the doubtful
subject of inherited mutilations. A man who is left-handed, and a shell in
which the spire turns in the wrong direction, are departures from the normal
though a symmetrical condition, and they are well known to be inherited.

Polydactylism.—Supernumerary fingers and toes are eminently liable,
as various authors have insisted, to transmission, but they are noticed
here chiefly on account of their occasional regrowth after amputation.
Polydactylism graduates[26] by multifarious steps from a mere
cutaneous appendage, not including any bone, to a double hand. But an
additional digit, supported on a metacarpal bone, and furnished with all
the proper muscles, nerves, and vessels, is sometimes so perfect, that it
escapes detection, unless the fingers are actually counted. Occasionally
there are several supernumerary digits; but usually only one, making
the total number six. This one may represent either a thumb or finger,
being attached to the inner or outer margin of the hand. Generally,
through the law of correlation, both hands and feet are similarly
affected. I have tabulated the cases recorded in various works or
privately communicated to me, of forty-six persons with extra digits on
one or both hands and feet; if in each case all four extremities had been
similarly affected, the table would have shown a total of ninety-two
hands and ninety-two feet each with six digits. As it is, seventy-three
hands and seventy-five feet were thus affected. This proves, in
contradiction to the result arrived at by Dr. Struthers,[27] that the hands
are not more frequently affected than the feet.
The presence of more than five digits is a great anomaly, for this
number is not normally exceeded by any mammal, bird, or existing
reptile.[28] Nevertheless, supernumerary digits are strongly inherited;

they have been transmitted through five generations; and in some
cases, after disappearing for one, two, or even three generations, have
reappeared through reversion. These facts are rendered, as Professor
Huxley has observed, more remarkable from its being known in most
cases that the affected person had not married one similarly affected. In
such cases the child of the fifth generation would have only 1-32nd
part of the blood of his first sedigitated ancestor. Other cases are
rendered remarkable by the affection gathering force, as Dr. Struthers
has shown, in each generation, though in each the affected person had
married one not affected; moreover such additional digits are often
amputated soon after birth, and can seldom have been strengthened by
use. Dr. Struthers gives the following instance: in the first generation
an additional digit appeared on one hand; in the second, on both hands;
in the third, three brothers had both hands, and one of the brothers a
foot affected; and in the fourth generation all four limbs were affected.
Yet we must not over-estimate the force of inheritance. Dr. Struthers
asserts that cases of non-inheritance and of the first appearance of
additional digits in unaffected families are much more frequent than
cases of inheritance. Many other deviations of structure, of a nature
almost as anomalous as supernumerary digits, such as deficient
phalanges, thickened joints, crooked fingers, &c., are in like manner
strongly inherited, and are equally subject to intermission with
reversion, though in such cases there is no reason to suppose that both
parents had been similarly affected.[29]
Additional digits have been observed in negroes as well as in other
races of man, and in several of the lower animals. Six toes have been
described on the hind feet of the newt (Salamandra cristata), and, as it
is said, of the frog. It deserves notice from what follows, that the six-
toed newt, though adult, had preserved some of its larval characters;
for part of the hyoidal apparatus, which is properly absorbed during the
act of metamorphosis, was retained. In the dog, six toes on the hinder
feet have been transmitted through three generations; and I have heard
of a race of six-toed cats. In several breeds of the fowl the hinder toe is
double, and is generally transmitted truly, as is well shown when
Dorkings are crossed with common four-toed breeds.[30] With animals
which have properly less than five digits, the number is sometimes

increased to five, especially in the front legs, though rarely carried
beyond that number; but this is due to the development of a digit
already existing in a more or less rudimentary state. Thus the dog has
properly four toes behind, but in the larger breeds a fifth toe is
commonly, though not perfectly, developed. Horses, which properly
have one toe alone fully developed with rudiments of the others, have
been described with each foot bearing two or three small separate
hoofs: analogous facts have been noticed with sheep, goats, and pigs.
[31]

The most interesting point with respect to supernumerary digits is their
occasional regrowth after amputation. Mr. White[32] describes a child,
three years old, with a thumb double from the first joint. He removed
the lesser thumb, which was furnished with a nail; but to his
astonishment it grew again, and reproduced a nail. The child was then
taken to an eminent London surgeon, and the newly-grown thumb was
wholly removed by its socket-joint, but again it grew and reproduced a
nail. Dr. Struthers mentions a case of partial regrowth of an additional
thumb, amputated when the child was three months old; and the late
Dr. Falconer communicated to me an analogous case which had fallen
under his own observation. A gentleman, who first called my attention
to this subject, has given me the following facts which occurred in his
own family. He himself, two brothers, and a sister were born with an
extra digit to each extremity. His parents were not affected, and there
was no tradition in the family, or in the village in which the family had
long resided, of any member having been thus affected. Whilst a child,
both additional toes, which were attached by bones, were rudely cut
off; but the stump of one grew again, and a second operation was
performed in his thirty-third year.
He has had fourteen children, of whom three have inherited additional
digits; and one of them, when about six weeks old, was operated on by
an eminent surgeon. The additional finger, which was attached by bone
to the outer side of the hand, was removed at the joint; the wound
healed, but immediately the digit began growing; and in about three
months' time the stump was removed for the second time by the root.
But it has since grown again, and is now fully a third of an inch in

length, including a bone; so that it will for the third time have to be
operated on.
Now the normal digits in adult man and other mammals, in birds, and,
as I believe, in true reptiles, have no power of regrowth. The nearest
approach to this power is exhibited by the occasional reappearance in
man of imperfect nails on the stumps of his fingers after amputation.
[33] But man in his embryonic condition has a considerable power of

reproduction, for Sir J. Simpson[34] has several times observed arms
which had been cut off in the womb by bands of false membrane, and
which had grown again to a certain extent. In one instance, the
extremity was "divided into three minute nodules, on two of which
small points of nails could be detected;" so that these nodules clearly
represented fingers in process of regrowth. When, however, we
descend to the lower vertebrate classes, which are generally looked at
as representing the higher classes in their embryonic condition, we find
ample powers of regrowth. Spallanzani[35] cut off the legs and tail of a
salamander six times, and Bonnet eight times, successively, and they
were reproduced. An additional digit beyond the proper number was
occasionally formed after Bonnet had cut off or had divided
longitudinally the hand or foot, and in one instance three additional
digits were thus formed.[36] These latter cases appear at first sight quite
distinct from the congenital production of additional digits in the
higher animals; but theoretically, as we shall see in a future chapter,
they probably present no real difference. The larvæ or tadpoles of the
tailless Batrachians, but not the adults,[37] are capable of reproducing
lost members.[38] Lastly, as I have been informed by Mr. J. J. Briggs
and Mr. F. Buckland, when portions of the pectoral and tail fins of
various fresh-water fish are cut off, they are perfectly reproduced in
about six weeks' time.

From these several facts we may infer that supernumerary digits in man
retain to a certain extent an embryonic condition, and that they resemble in
this respect the normal digits and limbs in the lower vertebrate classes.
They also resemble the digits of some of the lower animals in the number
exceeding five; for no mammal, bird, existing reptile, or amphibian (unless
the tubercle on the hind feet of the toad and other tailless Batrachians be

viewed as a digit) has more than five; whilst fishes sometimes have in their
pectoral fins as many as twenty metacarpal and phalangeal bones, which,
together with the bony filaments, apparently represent our digits with their
nails. So, again, in certain extinct reptiles, namely, the Ichthyopterygia, "the
digits may be seven, eight, or nine in number, a significant mark," says
Professor Owen, "of piscine affinity."[39]
We encounter much difficulty in attempting to reduce these various facts to
any rule or law. The inconstant number of the additional digits—their
irregular attachment to either the inner or outer margin of the hand—the
gradation which can be traced from a mere loose rudiment of a single digit
to a completely double hand—the occasional appearance of additional
digits in the salamander after a limb has been amputated—these various
facts appear to indicate mere fluctuating monstrosity; and this perhaps is all
that can be safely said. Nevertheless, as supernumerary digits in the higher
animals, from their power of regrowth and from the number thus acquired
exceeding five, partake of the nature of the digits in the lower vertebrate
animals;—as they occur by no means rarely, and are transmitted with
remarkable strength, though perhaps not more strongly than some other
anomalies;—and as with animals which have fewer than five digits, when
an additional one appears it is generally due to the development of a visible
rudiment;—we are led in all cases to suspect, that, although no actual
rudiment can be detected, yet that a latent tendency to the formation of an
additional digit exists in all mammals, including man. On this view, as we
shall more plainly see in the next chapter when discussing latent tendencies,
we should have to look at the whole case as one of reversion to an
enormously remote, lowly-organised, and multidigitate progenitor.

I may here allude to a class of facts closely allied to, but somewhat different
from, ordinary cases of inheritance. Sir H. Holland[40] states that brothers
and sisters of the same family are frequently affected, often at about the
same age, by the same peculiar disease, not known to have previously
occurred in the family. He specifies the occurrence of diabetes in three
brothers under ten years old; he also remarks that children of the same
family often exhibit in common infantile diseases the same peculiar
symptoms. My father mentioned to me the case of four brothers who died
between the ages of sixty and seventy, in the same highly peculiar comatose

state. An instance has been already given of supernumerary digits appearing
in four children out of six in a previously unaffected family. Dr. Devay
states[41] that two brothers married two sisters, their first-cousins, none of
the four nor any relation being an albino; but the seven children produced
from this double marriage were all perfect albinoes. Some of these cases, as
Mr. Sedgwick[42] has shown, are probably the result of reversion to a
remote ancestor, of whom no record had been preserved; and all these cases
are so far directly connected with inheritance that no doubt the children
inherited a similar constitution from their parents, and, from being exposed
to nearly similar conditions of life, it is not surprising that they should be
affected in the same manner and at the same period of life.

Most of the facts hitherto given have served to illustrate the force of
inheritance, but we must now consider cases, grouped as well as the subject
allows into classes, showing how feeble, capricious, or deficient the power
of inheritance sometimes is. When a new peculiarity first appears, we can
never predict whether it will be inherited. If both parents from their birth
present the same peculiarity, the probability is strong that it will be
transmitted to at least some of their offspring. We have seen that variegation
is transmitted much more feebly by seed from a branch which had become
variegated through bud-variation, than from plants which were variegated
as seedlings. With most plants the power of transmission notoriously
depends on some innate capacity in the individual: thus Vilmorin[43] raised
from a peculiarly coloured balsam some seedlings, which all resembled
their parent; but of these seedlings some failed to transmit the new
character, whilst others transmitted it to all their descendants during several
successive generations. So again with a variety of the rose, two plants alone
out of six were found by Vilmorin to be capable of transmitting the desired
character.

The weeping or pendulous growth of trees is strongly inherited in some
cases, and, without any assignable reason, feebly in other cases. I have
selected this character as an instance of capricious inheritance, because
it is certainly not proper to the parent-species, and because, both sexes
being borne on the same tree, both tend to transmit the same character.
Even supposing that there may have been in some instances crossing

with adjoining trees of the same species, it is not probable that all the
seedlings would have been thus affected. At Moccas Court there is a
famous weeping oak; many of its branches "are 30 feet long, and no
thicker in any part of this length than a common rope:" this tree
transmits its weeping character, in a greater or less degree, to all its
seedlings; some of the young oaks being so flexible that they have to
be supported by props; others not showing the weeping tendency till
about twenty years old.[44] Mr. Rivers fertilized, as he informs me, the
flowers of a new Belgian weeping thorn (Cratægus oxyacantha) with
pollen from a crimson not-weeping variety, and three young trees,
"now six or seven years old, show a decided tendency to be pendulous,
but as yet are not so much so as the mother-plant." According to Mr.
MacNab,[45] seedlings from a magnificent weeping birch (Betula alba),
in the Botanic Garden at Edinburgh, grew for the first ten or fifteen
years upright, but then all became weepers like their parent. A peach
with pendulous branches, like those of the weeping willow, has been
found capable of propagation by seed.[46] Lastly, a weeping and almost
prostrate yew (Taxus baccata) was found in a hedge in Shropshire; it
was a male, but one branch bore female flowers, and produced berries;
these, being sown, produced seventeen trees, all of which had exactly
the same peculiar habit with the parent-tree.[47]
These facts, it might have been thought, would have been sufficient to
render it probable that a pendulous habit would in all cases be strictly
inherited. But let us look to the other side. Mr. MacNab[48] sowed
seeds of the weeping beech (Fagus sylvanica), but succeeded in raising
only common beeches. Mr. Rivers, at my request, raised a number of
seedlings from three distinct varieties of weeping elm; and at least one
of the parent-trees was so situated that it could not have been crossed
by any other elm; but none of the young trees, now about a foot or two
in height, show the least signs of weeping. Mr. Rivers formerly sowed
above twenty thousand seeds of the weeping ash (Fraxinus excelsior),
and not a single seedling was in the least degree pendulous: in
Germany, M. Borchmeyer raised a thousand seedlings, with the same
result. Nevertheless, Mr. Anderson, of the Chelsea Botanic Garden, by
sowing seed from a weeping ash, which was found before the year
1780, in Cambridgeshire, raised several pendulous trees.[49] Professor

Henslow also informs me that some seedlings from a female weeping
ash in the Botanic Garden at Cambridge were at first a little pendulous,
but afterwards became quite upright: it is probable that this latter tree,
which transmits to a certain extent its pendulous habit, was derived by
a bud from the same original Cambridgeshire stock; whilst other
weeping ashes may have had a distinct origin. But the crowning case,
communicated to me by Mr. Rivers, which shows how capricious is the
inheritance of a pendulous habit, is that a variety of another species of
ash (F. lentiscifolia) which was formerly pendulous, "now about
twenty years old has long lost this habit, every shoot being remarkably
erect; but seedlings formerly raised from it were perfectly prostrate, the
stems not rising more than two inches above the ground." Thus the
weeping variety of the common ash, which has been extensively
propagated by buds during a long period, did not, with Mr. Rivers,
transmit its character to one seedling out of above twenty thousand;
whereas the weeping variety of a second species of ash, which could
not, whilst grown in the same garden, retain its own weeping character,
transmitted to its seedlings the pendulous habit in excess!
Many analogous facts could be given, showing how apparently
capricious is the principle of inheritance. All the seedlings from a
variety of the Barberry (B. vulgaris) with red leaves inherited the same
character; only about one-third of the seedlings of the copper Beech
(Fagus sylvatica) had purple leaves. Not one out of a hundred
seedlings of a variety of the Cerasus padus, with yellow fruit, bore
yellow fruit: one-twelfth of the seedlings of the variety of Cornus
mascula, with yellow fruit, came true:[50] and lastly, all the trees raised
by my father from a yellow-berried holly (Ilex aquifolium), found wild,
produced yellow berries. Vilmorin[51] observed in a bed of Saponaria
calabrica an extremely dwarf variety, and raised from it a large
number of seedlings; some of these partially resembled their parent,
and he selected their seed; but the grandchildren were not in the least
dwarfed: on the other hand, he observed a stunted and bushy variety of
Tagetes signata growing in the midst of the common varieties by
which it was probably crossed; for most of the seedlings raised from
this plant were intermediate in character, only two perfectly resembling

their parent; but seed saved from these two plants reproduced the new
variety so truly, that hardly any selection has since been necessary.
Flowers transmit their colour truly, or most capriciously. Many annuals
come true: thus I purchased German seeds of thirty-four named sub-
varieties of one race of ten-week stocks (Matthiola annua), and raised
a hundred and forty plants, all of which, with the exception of a single
plant, came true. In saying this, however, it must be understood that I
could distinguish only twenty kinds out of the thirty-four named sub-
varieties; nor did the colour of the flower always correspond with the
name affixed to the packet; but I say that they came true, because in
each of the thirty-six short rows every plant was absolutely alike, with
the one single exception. Again, I procured packets of German seed of
twenty-five named varieties of common and quilled asters, and raised a
hundred and twenty-four plants; of these, all except ten were true in the
above limited sense; and I considered even a wrong shade of colour as
false.
It is a singular circumstance that white varieties generally transmit
their colour much more truly than any other variety. This fact probably
stands in close relation with one observed by Verlot,[52] namely, that
flowers which are normally white rarely vary into any other colour. I
have found that the white varieties of Delphinium consolida and of the
Stock are the truest. It is, indeed, sufficient to look through a
nurseryman's seed-list, to see the large number of white varieties which
can be propagated by seed. The several coloured varieties of the sweet-
pea (Lathyrus odoratus) are very true; but I hear from Mr. Masters, of
Canterbury, who has particularly attended to this plant, that the white
variety is the truest. The hyacinth, when propagated by seed, is
extremely inconstant in colour, but "white hyacinths almost always
give by seed white-flowered plants;"[53] and Mr. Masters informs me
that the yellow varieties also reproduce their colour, but of different
shades. On the other hand, pink and blue varieties, the latter being the
natural colour, are not nearly so true: hence, as Mr. Masters has
remarked to me, "we see that a garden variety may acquire a more
permanent habit than a natural species;" but it should have been added,
that this occurs under cultivation, and therefore under changed
conditions.

With many flowers, especially perennials, nothing can be more
fluctuating than the colour of the seedlings, as is notoriously the case
with verbenas, carnations, dahlias, cinerarias, and others.[54] I sowed
seed of twelve named varieties of Snapdragon (Antirrhinum majus),
and utter confusion was the result. In most cases the extremely
fluctuating colour of seedling plants is probably in chief part due to
crosses between differently-coloured varieties during previous
generations. It is almost certain that this is the case with the polyanthus
and coloured primrose (Primula veris and vulgaris), from their
reciprocally dimorphic structure;[55] and these are plants which florists
speak of as never come true by seed: but if care be taken to prevent
crossing, neither species is by any means very inconstant in colour;
thus I raised twenty-three plants from a purple primrose, fertilised by
Mr. J. Scott with its own pollen, and eighteen came up purple of
different shades, and only five reverted to the ordinary yellow colour:
again, I raised twenty plants from a bright-red cowslip, similarly
treated by Mr. Scott, and every one perfectly resembled its parent in
colour, as likewise did, with the exception of a single plant, 73
grandchildren. Even with the most variable flowers, it is probable that
each delicate shade of colour might be permanently fixed so as to be
transmitted by seed, by cultivation in the same soil, by long-continued
selection, and especially by the prevention of crosses. I infer this from
certain annual larkspurs (Delphinium consolida and ajacis), of which
common seedlings present a greater diversity of colour than any other
plant known to me; yet on procuring seed of five named German
varieties of D. consolida, only nine plants out of ninety-four were
false; and the seedlings of six varieties of D. ajacis were true in the
same manner and degree as with the stocks above described. A
distinguished botanist maintains that the annual species of Delphinium
are always self-fertilised; therefore I may mention that thirty-two
flowers on a branch of D. consolida, enclosed in a net, yielded twenty-
seven capsules, with an average of 17.2 seed in each; whilst five
flowers, under the same net, which were artificially fertilised, in the
same manner as must be effected by bees during their incessant visits,
yielded five capsules with an average of 35.2 fine seed; and this shows
that the agency of insects is necessary for the full fertility of this plant.
Analogous facts could be given with respect to the crossing of many

other flowers, such as carnations, &c., of which the varieties fluctuate
much in colour.
As with flowers, so with our domesticated animals, no character is
more variable than colour, and probably in no animal more so than
with the horse. Yet with a little care in breeding, it appears that races of
any colour might soon be formed. Hofacker gives the result of
matching two hundred and sixteen mares of four different colours with
like-coloured stallions, without regard to the colour of their ancestors;
and of the two hundred and sixteen colts born, eleven alone failed to
inherit the colour of their parents: Autenrieth and Ammon assert that,
after two generations, colts of a uniform colour are produced with
certainty.[56]

In a few rare cases peculiarities fail to be inherited, apparently from the
force of inheritance being too strong. I have been assured by breeders of the
canary-bird that to get a good jonquil-coloured bird it does not answer to
pair two jonquils, as the colour then comes out too strong, or is even brown.
So again, if two crested canaries are paired, the young birds rarely inherit
this character:[57] for in crested birds a narrow space of bare skin is left on
the back of the head, where the feathers are up-turned to form the crest, and,
when both parents are thus characterised, the bareness becomes excessive,
and the crest itself fails to be developed. Mr. Hewitt, speaking of Laced
Sebright Bantams, says[58] that, "why this should be so, I know not, but I
am confident that those that are best laced frequently produce offspring
very far from perfect in their markings, whilst those exhibited by myself,
which have so often proved successful, were bred from the union of
heavily-laced birds with those that were scarcely sufficiently laced."
It is a singular fact that, although several deaf-mutes often occur in the
same family, and though their cousins and other relations are often in the
same condition, yet their parents are very rarely deaf-mutes. To give a
single instance: not one scholar out of 148, who were at the same time in
the London Institution, was the child of parents similarly afflicted. So again,
when a male or a female deaf-mute marries a sound person, their children
are most rarely affected: in Ireland out of 203 children thus produced one
alone was mute. Even when both parents have been deaf-mutes, as in the
case of forty-one marriages in the United States and of six in Ireland, only

two deaf and dumb children were produced. Mr. Sedgwick,[59] in
commenting on this remarkable and fortunate failure in the power of
transmission in the direct line, remarks that it may possibly be owing to
"excess having reversed the action of some natural law in development."
But it is safer in the present state of our knowledge to look at the whole
case as simply unintelligible.

With respect to the inheritance of structures mutilated by injuries or altered
by disease it is difficult to come to any definite conclusion. In some cases
mutilations have been practised for a vast number of generations without
any inherited result. Godron has remarked[60] that different races of man
have from time immemorial knocked out their upper incisors, cut off joints
of their fingers, made holes of immense size through the lobes of their ears
or through their nostrils, made deep gashes in various parts of their bodies,
and there is no reason whatever to suppose that these mutilations have ever
been inherited. Adhesions due to inflammation and pits from the small-pox
(and formerly many consecutive generations must have been thus pitted)
are not inherited. With respect to Jews, I have been assured by three
medical men of the Jewish faith that circumcision, which has been practised
for so many ages, has produced no inherited effect; Blumenbach, on the
other hand, asserts[61] that in Germany Jews are often born in a condition
rendering circumcision difficult, so that a name is here applied to them
signifying "born circumcised." The oak and other trees must have borne
galls from primeval times, yet they do not produce inherited excrescences;
many other such facts could be adduced.
On the other hand, various cases have been recorded of cats, dogs, and
horses, which have had their tails, legs, &c., amputated or injured,
producing offspring with the same parts ill-formed; but as it is not at all rare
for similar malformations to appear spontaneously, all such cases may be
due to mere coincidence. Nevertheless, Dr. Prosper Lucas has given, on
good authorities, such a long list of inherited injuries, that it is difficult not
to believe in them. Thus, a cow that had lost a horn from an accident with
consequent suppuration, produced three calves which were hornless on the
same side of the head. With the horse, there seems hardly a doubt that bony
exostoses on the legs, caused by too much travelling on hard roads, are
inherited. Blumenbach records the case of a man who had his little finger

on the right hand almost cut off, and which in consequence grew crooked,
and his sons had the same finger on the same hand similarly crooked. A
soldier, fifteen years before his marriage, lost his left eye from purulent
ophthalmia, and his two sons were microphthalmic on the same side.[62] In
all such cases, if truthfully reported, in which the parent has had an organ
injured on one side, and more than one child has been born with the same
organ affected on the same side, the chances against mere coincidence are
enormous. But perhaps the most remarkable and trustworthy fact is that
given by Dr. Brown-Séquard,[63] namely, that many young guinea-pigs
inherited an epileptic tendency from parents which had been subjected to a
particular operation, inducing in the course of a few weeks a convulsive
disease like epilepsy: and it should be especially noted that this eminent
physiologist bred a large number of guinea-pigs from animals which had
not been operated on, and not one of these manifested the epileptic
tendency. On the whole, we can hardly avoid admitting, that injuries and
mutilations, especially when followed by disease, or perhaps exclusively
when thus followed, are occasionally inherited.
Although many congenital monstrosities are inherited, of which examples
have already been given, and to which may be added the lately recorded
case of the transmission during a century of hare-lip with a cleft-palate in
the writer's own family,[64] yet other malformations are rarely or never
inherited. Of these later cases, many are probably due to injuries in the
womb or egg, and would come under the head of non-inherited injuries or
mutilations. With plants, a long catalogue of inherited monstrosities of the
most serious and diversified nature could easily be given; and with plants,
there is no reason to suppose that monstrosities are caused by direct injuries
to the seed or embryo.

Causes of Non-inheritance.
A large number of cases of non-inheritance are intelligible on the principle,
that a strong tendency to inheritance does exist, but that it is overborne by
hostile or unfavourable conditions of life. No one would expect that our
improved pigs, if forced during several generations to travel about and root
in the ground for their own subsistence, would transmit, as truly as they
now do, their tendency to fatten, and their short muzzles and legs. Dray-
horses assuredly would not long transmit their great size and massive limbs,

if compelled to live on a cold, damp mountainous region; we have indeed
evidence of such deterioration in the horses which have run wild on the
Falkland Islands. European dogs in India often fail to transmit their true
character. Our sheep in tropical countries lose their wool in a few
generations. There seems also to be a close relation between certain peculiar
pastures and the inheritance of an enlarged tail in fat-tailed sheep, which
form one of the most ancient breeds in the world. With plants, we have seen
that the American varieties of maize lose their proper character in the
course of two or three generations, when cultivated in Europe. Our
cabbages, which here come so true by seed, cannot form heads in hot
countries. Under changed circumstances, periodical habits of life soon fail
to be transmitted, as the period of maturity in summer and winter wheat,
barley, and vetches. So it is with animals; for instance, a person whose
statement I can trust, procured eggs of Aylesbury ducks from that town,
where they are kept in houses and are reared as early as possible for the
London market; the ducks bred from these eggs in a distant part of England,
hatched their first brood on January 24th, whilst common ducks, kept in the
same yard and treated in the same manner, did not hatch till the end of
March; and this shows that the period of hatching was inherited. But the
grandchildren of these Aylesbury ducks completely lost their early habit of
incubation, and hatched their eggs at the same time with the common ducks
of the same place.
Many cases of non-inheritance apparently result from the conditions of life
continually inducing fresh variability. We have seen that when the seeds of
pears, plums, apples, &c., are sown, the seedlings generally inherit some
degree of family likeness from the parent-variety. Mingled with these
seedlings, a few, and sometimes many, worthless, wild-looking plants
commonly appear; and their appearance may be attributed to the principle
of reversion. But scarcely a single seedling will be found perfectly to
resemble the parent-form; and this, I believe, may be accounted for by
constantly recurring variability induced by the conditions of life. I believe
in this, because it has been observed that certain fruit-trees truly propagate
their kind whilst growing on their own roots, but when grafted on other
stocks, and by this process their natural state is manifestly affected, they
produce seedlings which vary greatly, departing from the parental type in
many characters.[65] Metzger, as stated in the ninth chapter, found that

certain kinds of wheat brought from Spain and cultivated in Germany,
failed during many years to reproduce themselves truly; but that at last,
when accustomed to their new conditions, they ceased to be variable,—that
is, they became amenable to the power of inheritance. Nearly all the plants
which cannot be propagated with any approach to certainty by seed, are
kinds which have long been propagated by buds, cuttings, offsets, tubers,
&c., and have in consequence been frequently exposed during their
individual lives to widely diversified conditions of life. Plants thus
propagated become so variable, that they are subject, as we have seen in the
last chapter, even to bud-variation. Our domesticated animals, on the other
hand, are not exposed during their individual lives to such extremely
diversified conditions, and are not liable to such extreme variability;
therefore they do not lose the power of transmitting most of their
characteristic features. In the foregoing remarks on non-inheritance, crossed
breeds are of course excluded, as their diversity mainly depends on the
unequal development of characters derived from either parent, modified by
the principles of reversion and prepotency.

Conclusion.
It has, I think, been shown in the early part of this chapter how strongly new
characters of the most diversified nature, whether normal or abnormal,
injurious or beneficial, whether affecting organs of the highest or most
trifling importance, are inherited. Contrary to the common opinion, it is
often sufficient for the inheritance of some peculiar character, that one
parent alone should possess it, as in most cases in which the rarer anomalies
have been transmitted. But the power of transmission is extremely variable:
in a number of individuals descended from the same parents, and treated in
the same manner, some display this power in a perfect manner, and in some
it is quite deficient; and for this difference no reason can be assigned. In
some cases the effects of injuries or mutilations apparently are inherited;
and we shall see in a future chapter that the effects of the long-continued
use and disuse of parts are certainly inherited. Even those characters which
are considered the most fluctuating, such as colour, are with rare exceptions
transmitted much more forcibly than is generally supposed. The wonder,
indeed, in all cases is not that any character should be transmitted, but that
the power of inheritance should ever fail. The checks to inheritance, as far
as we know them, are, firstly, circumstances hostile to the particular

character in question; secondly, conditions of life incessantly inducing fresh
variability; and lastly, the crossing of distinct varieties during some
previous generation, together with reversion or atavism—that is, the
tendency in the child to resemble its grand-parents or more remote
ancestors instead of its immediate parents. This latter subject will be fully
discussed in the following chapter.

CHAPTER XIII.

INHERITANCE continued—REVERSION OR ATAVISM.

DIFFERENT FORMS OF REVERSION—IN PURE OR UNCROSSED BREEDS, AS IN
PIGEONS, FOWLS, HORNLESS CATTLE AND SHEEP, IN CULTIVATED PLANTS—
REVERSION IN FERAL ANIMALS AND PLANTS—REVERSION IN CROSSED
VARIETIES AND SPECIES—REVERSION THROUGH BUD-PROPAGATION, AND BY
SEGMENTS IN THE SAME FLOWER OR FRUIT—IN DIFFERENT PARTS OF THE
BODY IN THE SAME ANIMAL—THE ACT OF CROSSING A DIRECT CAUSE OF
REVERSION, VARIOUS CASES OF, WITH INSTINCTS—OTHER PROXIMATE
CAUSES OF REVERSION—LATENT CHARACTERS—SECONDARY SEXUAL
CHARACTERS—UNEQUAL DEVELOPMENT OF THE TWO SIDES OF THE BODY—
APPEARANCE WITH ADVANCING AGE OF CHARACTERS DERIVED FROM A
CROSS—THE GERM WITH ALL ITS LATENT CHARACTERS A WONDERFUL
OBJECT—MONSTROSITIES—PELORIC FLOWERS DUE IN SOME CASES TO
REVERSION.

The great principle of inheritance to be discussed in this chapter has been
recognised by agriculturists and authors of various nations, as shown by the
scientific term Atavism, derived from atavus, an ancestor; by the English
terms of Reversion, or Throwing back; by the French Pas-en-arrière; and by
the German Rück-schlag, or Rück-schritt. When the child resembles either
grandparent more closely than its immediate parents, our attention is not
much arrested, though in truth the fact is highly remarkable; but when the
child resembles some remote ancestor, or some distant member in a
collateral line,—and we must attribute the latter case to the descent of all
the members from a common progenitor,—we feel a just degree of
astonishment. When one parent alone displays some newly-acquired and

generally inheritable character, and the offspring do not inherit it, the cause
may lie in the other parent having the power of prepotent transmission. But
when both parents are similarly characterised, and the child does not,
whatever the cause may be, inherit the character in question, but resembles
its grandparents, we have one of the simplest cases of reversion. We
continually see another and even more simple case of atavism, though not
generally included under this head, namely, when the son more closely
resembles his maternal than his paternal grandsire in some male attribute, as
in any peculiarity in the beard of man, the horns of the bull, the hackles or
comb of the cock, or, as in certain diseases necessarily confined to the male
sex; for the mother cannot possess or exhibit such male attributes, yet the
child has inherited them, through her blood, from his maternal grandsire.
The cases of reversion may be divided into two main classes, which,
however, in some instances, blend into each other; namely, first, those
occurring in a variety or race which has not been crossed, but has lost by
variation some character that it formerly possessed, and which afterwards
reappears. The second class includes all cases in which a distinguishable
individual, sub-variety, race, or species, has at some former period been
crossed with a distinct form, and a character derived from this cross, after
having disappeared during one or several generations, suddenly reappears.
A third class, differing only in the manner of reproduction, might be formed
to include all cases of reversion effected by means of buds, and therefore
independent of true or seminal generation. Perhaps even a fourth class
might be instituted, to include reversions by segments in the same
individual flower or fruit, and in different parts of the body in the same
individual animal as it grows old. But the two first main classes will be
sufficient for our purpose.

Reversion to lost Characters by pure or uncrossed forms.—Striking
instances of this first class of cases were given in the sixth chapter, namely,
of the occasional reappearance, in variously-coloured pure breeds of the
pigeon, of blue birds with all the marks which characterise the wild
Columba livia. Similar cases were given in the case of the fowl. With the
common ass, as we now know that the legs of the wild progenitor are
striped, we may feel assured that the occasional appearance of such stripes
in the domestic animal is a case of simple reversion. But I shall be

compelled to refer again to these cases, and therefore will here pass them
over.
The aboriginal species from which our domesticated cattle and sheep are
descended, no doubt possessed horns; but several hornless breeds are now
well established. Yet in these—for instance, in Southdown sheep—"it is not
unusual to find among the male lambs some with small horns." The horns,
which thus occasionally reappear in other polled breeds, either "grow to the
full size, or are curiously attached to the skin alone and hang loosely down,
or drop off."[66] The Galloways and Suffolk cattle have been hornless for
the last 100 or 150 years, but a horned calf, with the horn often loosely
attached, is occasionally born.[67]
There is reason to believe that sheep in their early domesticated condition
were "brown or dingy black;" but even in the time of David certain flocks
were spoken of as white as snow. During the classical period the sheep of
Spain are described by several ancient authors as being black, red, or tawny.
[68] At the present day, notwithstanding the great care which is taken to

prevent it, particoloured lambs and some entirely black are occasionally
dropped by our most highly improved and valued breeds, such as the
Southdowns. Since the time of the famous Bakewell, during the last
century, the Leicester sheep have been bred with the most scrupulous care;
yet occasionally grey-faced, or black-spotted, or wholly black lambs appear.
[69] This occurs still more frequently with the less improved breeds, such as

the Norfolks.[70] As bearing on this tendency in sheep to revert to dark
colours, I may state (though in doing so I trench on the reversion of crossed
breeds, and likewise on the subject of prepotency) that the Rev. W. D. Fox
was informed that seven white Southdown ewes were put to a so-called
Spanish ram, which had two small black spots on his sides, and they
produced thirteen lambs, all perfectly black. Mr. Fox believes that this ram
belonged to a breed which he has himself kept, and which is always spotted
with black and white; and he finds that Leicester sheep crossed by rams of
this breed always produce black lambs: he has gone on recrossing these
crossed sheep with pure white Leicesters during three successive
generations, but always with the same result. Mr. Fox was also told by the
friend from whom the spotted breed was procured, that he likewise had

gone on for six or seven generations crossing with white sheep, but still
black lambs were invariably produced.
Similar facts could be given with respect to tailless breeds of various
animals. For instance, Mr. Hewitt[71] states that chickens bred from some
Rumpless fowls, which were reckoned so good that they won a prize at an
exhibition, "in a considerable number of instances were furnished with fully
developed tail-feathers." On inquiry, the original breeder of these fowls
stated that, from the time when he had first kept them, they had often
produced fowls furnished with tails; but that these latter would again
reproduce rumpless chickens.
Analogous cases of reversion occur in the vegetable kingdom; thus "from
seeds gathered from the finest cultivated varieties of Heartsease (Viola
tricolor), plants perfectly wild both in their foliage and their flowers are
frequently produced;"[72] but the reversion in this instance is not to a very
ancient period, for the best existing varieties of the heartsease are of
comparatively modern origin. With most of our cultivated vegetables there
is some tendency to reversion to what is known to be, or may be presumed
to be, their aboriginal state; and this would be more evident if gardeners did
not generally look over their beds of seedlings, and pull up the false plants
or "rogues" as they are called. It has already been remarked, that some few
seedling apples and pears generally resemble, but apparently are not
identical with, the wild trees from which they are descended. In our
turnip[73] and carrot-beds a few plants often "break"—that is, flower too
soon; and their roots are generally found to be hard and stringy, as in the
parent-species. By the aid of a little selection, carried on during a few
generations, most of our cultivated plants could probably be brought back,
without any great change in their conditions of life, to a wild or nearly wild
condition: Mr. Buckman has effected this with the parsnip;[74] and Mr.
Hewett C. Watson, as he informs me, selected, during three generations,
"the most diverging plants of Scotch kail, perhaps one of the least modified
varieties of the cabbage; and in the third generation some of the plants came
very close to the forms now established in England about old castle-walls,
and called indigenous."

Reversion in Animals and Plants which have run wild.—In the cases
hitherto considered, the reverting animals and plants have not been exposed
to any great or abrupt change in their conditions of life which could have
induced this tendency; but it is very different with animals and plants which
have become feral or run wild. It has been repeatedly asserted in the most
positive manner by various authors, that feral animals and plants invariably
return to their primitive specific type. It is curious on what little evidence
this belief rests. Many of our domesticated animals could not subsist in a
wild state; thus, the more highly improved breeds of the pigeon will not
"field" or search for their own food. Sheep have never become feral, and
would be destroyed by almost every beast of prey. In several cases we do
not know the aboriginal parent-species, and cannot possibly tell whether or
not there has been any close degree of reversion. It is not known in any
instance what variety was first turned out; several varieties have probably in
some cases run wild, and their crossing alone would tend to obliterate their
proper character. Our domesticated animals and plants, when they run wild,
must always be exposed to new conditions of life, for, as Mr. Wallace[75]
has well remarked, they have to obtain their own food, and are exposed to
competition with the native productions. Under these circumstances, if our
domesticated animals did not undergo change of some kind, the result
would be quite opposed to the conclusions arrived at in this work.
Nevertheless, I do not doubt that the simple fact of animals and plants
becoming feral, does cause some tendency to reversion to the primitive
state; though this tendency has been much exaggerated by some authors.

I will briefly run through the recorded cases. With neither horses nor
cattle is the primitive stock known; and it has been shown in former
chapters that they have assumed different colours in different
countries. Thus the horses which have run wild in South America are
generally brownish-bay, and in the East dun-coloured; their heads have
become larger and coarser, and this may be due to reversion. No
careful description has been given of the feral goat. Dogs which have
run wild in various countries have hardly anywhere assumed a uniform
character; but they are probably descended from several domestic
races, and aboriginally from several distinct species. Feral cats, both in
Europe and La Plata, are regularly striped; in some cases they have
grown to an unusually large size, but do not differ from the domestic

animal in any other character. When variously-coloured tame rabbits
are turned out in Europe, they generally reacquire the colouring of the
wild animal; there can be no doubt that this does really occur, but we
should remember that oddly-coloured and conspicuous animals would
suffer much from beasts of prey and from being easily shot; this at
least was the opinion of a gentleman who tried to stock his woods with
a nearly white variety; and when thus destroyed, they would in truth be
supplanted by, instead of being transformed into, the common rabbit.
We have seen that the feral rabbits of Jamaica, and especially of Porto
Santo, have assumed new colours and other new characters. The best
known case of reversion, and that on which the widely-spread belief in
its universality apparently rests, is that of pigs. These animals have run
wild in the West Indies, South America, and the Falkland Islands, and
have everywhere acquired the dark colour, the thick bristles, and great
tusks of the wild boar; and the young have reacquired longitudinal
stripes. But even in the case of the pig, Roulin describes the half-wild
animals in different parts of South America as differing in several
respects. In Louisiana the pig[76] has run wild, and is said to differ a
little in form, and much in colour, from the domestic animal, yet does
not closely resemble the wild boar of Europe. With pigeons and fowls,
[77]
it is not known what variety was first turned out, nor what
character the feral birds have assumed. The guinea-fowl in the West
Indies, when feral, seems to vary more than in the domesticated state.

With respect to plants run wild, Dr. Hooker[78] has strongly insisted on
what slight evidence the common belief in their power of reversion
rests. Godron[79] describes wild turnips, carrots, and celery; but these
plants in their cultivated state hardly differ from their wild prototypes,
except in the succulency and enlargement of certain parts,—characters
which would be surely lost by plants growing in a poor soil and
struggling with other plants. No cultivated plant has run wild on so
enormous a scale as the cardoon (Cynara cardunculus) in La Plata.
Every botanist who has seen it growing there, in vast beds, as high as a
horse's back, has been struck with its peculiar appearance; but whether
it differs in any important point from the cultivated Spanish form,
which is said not to be prickly like its American descendant, or

whether it differs from he wild Mediterranean species, which is said
not to be social, I do not know.

Reversion to Characters derived from a Cross, in the case of Sub-varieties,
Races, and Species.—When an individual having some recognizable
peculiarity unites with another of the same sub-variety, not having the
peculiarity in question, it often reappears in the descendants after an
interval of several generations. Every one must have noticed, or heard from
old people of children closely resembling in appearance or mental
disposition, or in so small and complex a character as expression, one of
their grandparents, or some more distant collateral relation. Very many
anomalies of structure and diseases,[80] of which instances have been given
in the last chapter, have come into a family from one parent, and have
reappeared in the progeny after passing over two or three generations. The
following case has been communicated to me on good authority, and may, I
believe, be fully trusted: a pointer-bitch produced seven puppies; four were
marked with blue and white, which is so unusual a colour with pointers that
she was thought to have played false with one of the greyhounds, and the
whole litter was condemned; but the gamekeeper was permitted to save one
as a curiosity. Two years afterwards a friend of the owner saw the young
dog, and declared that he was the image of his old pointer-bitch Sappho, the
only blue and white pointer of pure descent which he had ever seen. This
led to close inquiry, and it was proved that he was the great-great-grandson
of Sappho; so that, according to the common expression, he had only 1-16th
of her blood in his veins. Here it can hardly be doubted that a character
derived from a cross with an individual of the same variety reappeared after
passing over three generations.
When two distinct races are crossed, it is notorious that the tendency in the
offspring to revert to one or both parent-forms is strong, and endures for
many generations. I have myself seen the clearest evidence of this in
crossed pigeons and with various plants. Mr. Sidney[81] states that, in a litter
of Essex pigs, two young ones appeared which were the image of the
Berkshire boar that had been used twenty-eight years before in giving size
and constitution to the breed. I observed in the farmyard at Betley Hall
some fowls showing a strong likeness to the Malay breed, and was told by

Mr. Tollet that he had forty years before crossed his birds with Malays; and
that, though he had at first attempted to get rid of this strain, he had
subsequently given up the attempt in despair, as the Malay character would
reappear.
This strong tendency in crossed breeds to revert has given rise to endless
discussions in how many generations after a single cross, either with a
distinct breed or merely with an inferior animal, the breed may be
considered as pure, and free from all danger of reversion. No one supposes
that less than three generations suffices, and most breeders think that six,
seven, or eight are necessary, and some go to still greater lengths.[82] But
neither in the case of a breed which has been contaminated by a single
cross, nor when, in the attempt to form an intermediate breed, half-bred
animals have been matched together during many generations, can any rule
be laid down how soon the tendency to reversion will be obliterated. It
depends on the difference in the strength or prepotency of transmission in
the two parent-forms, on their actual amount of difference, and on the
nature of the conditions of life to which the crossed offspring are exposed.
But we must be careful not to confound these cases of reversion to
characters gained from a cross, with those given under the first class, in
which characters originally common to both parents, but lost at some
former period, reappear; for such characters may recur after an almost
indefinite number of generations.
The law of reversion is equally powerful with hybrids, when they are
sufficiently fertile to breed together, or when they are repeatedly crossed
with either pure parent-form, as with mongrels. It is not necessary to give
instances, for in the case of plants almost every one who has worked on this
subject from the time of Kölreuter to the present day has insisted on this
tendency. Gärtner has recorded some good instances; but no one has given
more striking cases than Naudin.[83] The tendency differs in degree or
strength in different groups, and partly depends, as we shall presently see,
on the fact of the parent-plants having been long cultivated. Although the
tendency to reversion is extremely general with nearly all mongrels and
hybrids, it cannot be considered as invariably characteristic of them; there
is, also, reason to believe that it may be mastered by long-continued
selection; but these subjects will more properly be discussed in a future
chapter on Crossing. From what we see of the power and scope of

reversion, both in pure races and when varieties or species are crossed, we
may infer that characters of almost every kind are capable of reappearance
after having been lost for a great length of time. But it does not follow from
this that in each particular case certain characters will reappear: for
instance, this will not occur when a race is crossed with another endowed
with prepotency of transmission. In some few cases the power of reversion
wholly fails, without our being able to assign any cause for the failure: thus
it has been stated that in a French family in which 85 out of above 600
members, during six generations, had been subject to night-blindness,
"there has not been a single example of this affection in the children of
parents who were themselves free from it."[84]

Reversion through Bud-propagation—Partial Reversion, by segments in the
same flower or fruit, or in different parts of the body in the same individual
animal.—In the eleventh chapter, many cases of reversion by buds,
independently of seminal generation, were given—as when a leaf-bud on a
variegated, curled, or laciniated variety suddenly reassumes its proper
character; or as when a Provence-rose appears on a moss-rose, or a peach
on a nectarine-tree. In some of these cases only half the flower or fruit, or a
smaller segment, or mere stripes, reassumed their former character; and
here we have with buds reversion by segments. Vilmorin[85] has also
recorded several cases with plants derived from seed, of flowers reverting
by stripes or blotches to their primitive colours: he states that in all such
cases a white or pale-coloured variety must first be formed, and, when this
is propagated for a length of time by seed, striped seedlings occasionally
make their appearance; and these can afterwards by care be multiplied by
seed.
The stripes and segments just referred to are not due, as far as is known, to
reversion to characters derived from a cross, but to characters lost by
variation. These cases, however, as Naudin[86] insists in his discussion on
disjunction of character, are closely analogous with those given in the
eleventh chapter, in which crossed plants are known to have produced half-
and-half or striped flowers and fruit, or distinct kinds of flowers on the
same root resembling the two parent-forms. Many piebald animals probably
come under this same head. Such cases, as we shall see in the chapter on
Crossing, apparently result from certain characters not readily blending

together, and, as a consequence of this incapacity for fusion, the offspring
either perfectly resemble one of their two parents, or resemble one parent in
one part and the other parent in another part; or whilst young are
intermediate in character, but with advancing age revert wholly or by
segments to either parent-form, or to both. Thus young trees of the Cytisus
adami are intermediate in foliage and flowers between the two parent-
forms; but when older the buds continually revert either partially or wholly
to both forms. The cases given in the eleventh chapter on the changes which
occurred during growth in crossed plants of Tropæolum, Cereus, Datura,
and Lathyrus are all analogous. As however these plants are hybrids of the
first generation, and as their buds after a time come to resemble their
parents and not their grandparents, these cases do not at first appear to come
under the law of reversion in the ordinary sense of the word; nevertheless,
as the change is effected through a succession of bud-generations on the
same plant, they may be thus included.
Analogous facts have been observed in the animal kingdom, and are more
remarkable, as they occur strictly in the same individual, and not as with
plants through a succession of bud-generations. With animals the act of
reversion, if it can be so designated, does not pass over a true generation,
but merely over the early stages of growth in the same individual. For
instance, I crossed several white hens with a black cock, and many of the
chickens were during the first year perfectly white, but acquired during the
second year black feathers; on the other hand, some of the chickens which
were at first black became during the second year piebald with white. A
great breeder[87] says, that a Pencilled Brahma hen which has any of the
blood of the Light Brahma in her, will "occasionally produce a pullet well
pencilled during the first year, but she will most likely moult brown on the
shoulders and become quite unlike her original colours in the second year."
The same thing occurs with Light Brahmas if of impure blood. I have
observed exactly similar cases with the crossed offspring from differently
coloured pigeons. But here is a more remarkable fact: I crossed a turbit,
which has a frill formed by the feathers being reversed on its breast, with a
trumpeter; and one of the young pigeons thus raised showed at first not a
trace of the frill, but, after moulting thrice, a small yet unmistakably distinct
frill appeared on its breast. According to Girou,[88] calves produced from a

red cow by a black bull, or from a black cow by a red bull, are not rarely
born red, and subsequently become black.
In the foregoing cases, the characters which appear with advancing age are
the result of a cross in the previous or some former generation; but in the
following cases, the characters which thus reappear formerly appertained to
the species, and were lost at a more or less remote epoch. Thus, according
to Azara,[89] the calves of a hornless race of cattle which originated in
Corrientes, though at first quite hornless, as they become adult sometimes
acquire small, crooked, and loose horns; and these in succeeding years
occasionally become attached to the skull. White and black bantams, both
of which generally breed true, sometimes assume as they grow old a saffron
or red plumage. For instance, a first-rate black bantam has been described,
which during three seasons was perfectly black, but then annually became
more and more red; and it deserves notice that this tendency to change,
whenever it occurs in a bantam, "is almost certain to prove hereditary."[90]
The cuckoo or blue-mottled Dorking cock, when old, is liable to acquire
yellow or orange hackles in place of his proper bluish-grey hackles.[91]
Now, as Gallus bankiva is coloured red and orange, and as Dorking fowls
and both kinds of bantams are descended from this species, we can hardly
doubt that the change which occasionally occurs in the plumage of these
birds as their age advances, results from a tendency in the individual to
revert to the primitive type.

Crossing as a direct cause of Reversion.—It has long been notorious that
hybrids and mongrels often revert to both or to one of their parent-forms,
after an interval of from two to seven or eight, or according to some
authorities even a greater number of generations. But that the act of
crossing in itself gives an impulse towards reversion, as shown by the
reappearance of long-lost characters, has never, I believe, been hitherto
proved. The proof lies in certain peculiarities, which do not characterise the
immediate parents, and therefore cannot have been derived from them,
frequently appearing in the offspring of two breeds when crossed, which
peculiarities never appear, or appear with extreme rarity, in these same
breeds, as long as they are precluded from crossing. As this conclusion
seems to me highly curious and novel, I will give the evidence in detail.

My attention was first called to this subject, and I was led to make
numerous experiments, by MM. Boitard and Corbié having stated that,
when they crossed certain breeds, pigeons coloured like the wild C.
livia, or the common dovecot, namely, slaty-blue, with double black
wing-bars, sometimes chequered with black, white loins, the tail barred
with black, with the outer feathers edged with white, were almost
invariably produced. The breeds which I crossed, and the remarkable
results attained, have been fully described in the sixth chapter. I
selected pigeons, belonging to true and ancient breeds, which had not a
trace of blue or any of the above specified marks; but when crossed,
and their mongrels recrossed, young birds were continually produced,
more or less plainly coloured slaty-blue, with some or all of the proper
characteristic marks. I may recall to the reader's memory one case,
namely, that of a pigeon, hardly distinguishable from the wild Shetland
species, the grandchild of a red-spot, white fantail, and two black
barbs, from any of which, when purely-bred, the production of a
pigeon coloured like the wild C. livia would have been almost a
prodigy.
I was thus led to make the experiments, recorded in the seventh
chapter, on fowls. I selected long-established, pure breeds, in which
there was not a trace of red, yet in several of the mongrels feathers of
this colour appeared; and one magnificent bird, the offspring of a black
Spanish cock and white Silk hen, was coloured almost exactly like the
wild Gallus bankiva. All who know anything of the breeding of poultry
will admit that tens of thousands of pure Spanish and of pure white
Silk fowls might have been reared without the appearance of a red
feather. The fact, given on the authority of Mr. Tegetmeier, of the
frequent appearance, in mongrel fowls, of pencilled or transversely-
barred feathers, like those common to many gallinaceous birds, is
likewise apparently a case of reversion to a character formerly
possessed by some ancient progenitor of the family. I owe to the
kindness of this same excellent observer the inspection of some neck-
hackles and tail-feathers from a hybrid between the common fowl and
a very distinct species, the Gallus varius; and these feathers are
transversely striped in a conspicuous manner with dark metallic blue

and grey, a character which could not have been derived from either
immediate parent.
I have been informed by Mr. B. P. Brent, that he crossed a white
Aylesbury drake and a black so-called Labrador duck, both of which
are true breeds, and he obtained a young drake closely like the mallard
(A. boschas). Of the musk-duck (A. moschata, Linn.) there are two
sub-breeds, namely, white and slate-coloured; and these I am informed
breed true, or nearly true. But the Rev. W. D. Fox tells me that, by
putting a white drake to a slate-coloured duck, black birds, pied with
white, like the wild musk-duck, were always produced.
We have seen in the fourth chapter, that the so-called Himalayan
rabbit, with its snow-white body, black ears, nose, tail, and feet, breeds
perfectly true. This race is known to have been formed by the union of
two varieties of silver-grey rabbits. Now, when a Himalayan doe was
crossed by a sandy-coloured buck, a silver-grey rabbit was produced;
and this is evidently a case of reversion to one of the parent varieties.
The young of the Himalayan rabbit are born snow-white, and the dark
marks do not appear until some time subsequently; but occasionally
young Himalayan rabbits are born of a light silver-grey, which colour
soon disappears; so that here we have a trace of reversion, during an
early period of life, to the parent-varieties, independently of any recent
cross.
In the third chapter is was shown that at an ancient period some breeds
of cattle in the wilder parts of Britain were white with dark ears, and
that the cattle now kept half wild in certain parks, and those which
have run quite wild in two distant parts of the world, are likewise thus
coloured. Now, an experienced breeder, Mr. J. Beasley, of
Northamptonshire,[92] crossed some carefully selected West Highland
cows with purely-bred shorthorn bulls. The bulls were red, red and
white, or dark roan; and the Highland cows were all of a red colour,
inclining to a light or yellow shade. But a considerable number of the
offspring—and Mr. Beasley calls attention to this as a remarkable fact
—were white, or white with red ears. Bearing in mind that none of the
parents were white, and that they were purely-bred animals, it is highly
probable that here the offspring reverted, in consequence of the cross,

to the colour either of the aboriginal parent-species or of some ancient
and half-wild parent-breed. The following case, perhaps, comes under
the same head: cows in their natural state have their udders but little
developed, and do not yield nearly so much milk as our domesticated
animals. Now there is some reason to believe[93] that cross-bred
animals between two kinds, both of which are good milkers, such as
Alderneys and Shorthorns, often turn out worthless in this respect.
In the chapter on the Horse reasons were assigned for believing that
the primitive stock was striped and dun-coloured; and details were
given, showing that in all parts of the world stripes of a dark colour
frequently appear along the spine, across the legs, and on the
shoulders, where they are occasionally double or treble, and even
sometimes on the face and body of horses of all breeds and of all
colours. But the stripes appear most frequently on the various kinds of
duns. They may sometimes plainly be seen on foals, and subsequently
disappear. The dun-colour and the stripes are strongly transmitted
when a horse thus characterised is crossed with any other; but I was
not able to prove that striped duns are generally produced from the
crossing of two distinct breeds, neither of which are duns, though this
does sometimes occur.
The legs of the ass are often striped, and this may be considered as a
reversion to the wild parent-form, the Asinus tæniopus of Abyssinia,[94]
which is thus striped. In the domestic animal the stripes on the
shoulder are occasionally double, or forked at the extremity, as in
certain zebrine species. There is reason to believe that the foal is
frequently more plainly striped on the legs than the adult animal. As
with the horse, I have not acquired any distinct evidence that the
crossing of differently-coloured varieties of the ass brings out the
stripes.
But now let us turn to the result of crossing the horse and ass. Although
mules are not nearly so numerous in England as asses, I have seen a
much greater number with striped legs, and with the stripes far more
conspicuous than in either parent-form. Such mules are generally light-
coloured, and might be called fallow-duns. The shoulder-stripe in one
instance was deeply forked at the extremity, and in another instance

was double, though united in the middle. Mr. Martin gives a figure of a
Spanish mule with strong zebra-like marks on its legs,[95] and remarks,
that mules are particularly liable to be thus striped on their legs. In
South America, according to Roulin,[96] such stripes are more frequent
and conspicuous in the mule than in the ass. In the United States, Mr.
Gosse,[97] speaking of these animals, says, "that in a great number,
perhaps in nine out of every ten, the legs are banded with transverse
dark stripes."
Many years ago I saw in the Zoological Gardens a curious triple
hybrid, from a bay mare, by a hybrid from a male ass and female
zebra. This animal when old had hardly any stripes; but I was assured
by the superintendent, that when young it had shoulder-stripes, and
faint stripes on its flanks and legs. I mention this case more especially
as an instance of the stripes being much plainer during youth than in
old age.
As the zebra has such conspicuously striped legs, it might have been
expected that the hybrids from this animal and the common ass would
have had their legs in some degree striped; but it appears from the
figures given in Dr. Gray's 'Knowsley Gleanings,' and still more
plainly from that given by Geoffroy and F. Cuvier,[98] that the legs are
much more conspicuously striped than the rest of the body; and this
fact is intelligible only on the belief that the ass aids in giving, through
the power of reversion, this character to its hybrid offspring.
The quagga is banded over the whole front part of its body like a zebra,
but has no stripes on its legs, or mere traces of them. But in the famous
hybrid bred by Lord Morton,[99] from a chesnut, nearly purely-bred,
Arabian mare, by a male quagga, the stripes were "more strongly
defined and darker than those on the legs of the quagga." The mare
was subsequently put to a black Arabian horse, and bore two colts,
both of which, as formerly stated, were plainly striped on the legs, and
one of them likewise had stripes on the neck and body.

The Asinus Indicus[100] is characterised by a spinal stripe, without
shoulder or leg stripes; but traces of these latter stripes may
occasionally be seen even in the adult;[101] and Colonel S. Poole, who

has had ample opportunities for observation, informs me that in the
foal, when first born, the head and legs are often striped, but the
shoulder-stripe is not so distinct as in the domestic ass; all these
stripes, excepting that along the spine, soon disappear. Now a hybrid,
raised at Knowsley[102] from a female of this species by a male
domestic ass, had all four legs transversely and conspicuously striped,
had three short stripes on each shoulder, and had even some zebra-like
stripes on its face! Dr. Gray informs me that he has seen a second
hybrid of the same parentage similarly striped.

From these facts we see that the crossing of the several equine species tends
in a marked manner to cause stripes to appear on various parts of the body,
especially on the legs. As we do not know whether the primordial parent of
the genus was striped, the appearance of the stripes can only hypothetically
be attributed to reversion. But most persons, after considering the many
undoubted cases of variously coloured marks reappearing by reversion in
crossed pigeons, fowls, ducks, &c., will come to the same conclusion with
respect to the horse-genus; and in this case we must admit that the
progenitor of the group was striped on the legs, shoulders, face, and
probably over the whole body, like a zebra. If we reject this view, the
frequent and almost regular appearance of stripes in the several foregoing
hybrids is left without any explanation.

It would appear that with crossed animals a similar tendency to the recovery
of lost characters holds good even with instincts. There are some breeds of
fowls which are called "everlasting layers," because they have lost the
instinct of incubation; and so rare is it for them to incubate that I have seen
notices published in works on poultry, when hens of such breeds have taken
to sit.[103] Yet the aboriginal species was of course a good incubator; for
with birds in a state of nature hardly any instinct is so strong as this. Now,
so many cases have been recorded of the crossed offspring from two races,
neither of which are incubators, becoming first-rate sitters, that the
reappearance of this instinct must be attributed to reversion from crossing.
One author goes so far as to say, "that a cross between two non-sitting
varieties almost invariably produces a mongrel that becomes broody, and
sits with remarkable steadiness."[104] Another author, after giving a striking

example, remarks that the fact can be explained only on the principle that
"two negatives make a positive." It cannot, however, be maintained that
hens produced from a cross between two non-sitting breeds invariably
recover their lost instinct, any more than that crossed fowls or pigeons
invariably recover the red or blue plumage of their prototypes. I raised
several chickens from a Polish hen by a Spanish cock,—breeds which do
not incubate,—and none of the young hens at first recovered their instinct,
and this appeared to afford a well-marked exception to the foregoing rule;
but one of these hens, the only one which was preserved, in the third year
sat well on her eggs and reared a brood of chickens. So that here we have
the appearance with advancing age of a primitive instinct, in the same
manner as we have seen that the red plumage of the Gallus bankiva is
sometimes reacquired by crossed and purely-bred fowls of various kinds as
they grow old.
The parents of all our domesticated animals were of course aboriginally
wild in disposition; and when a domesticated species is crossed with a
distinct species, whether this is a domesticated or only tamed animal, the
hybrids are often wild to such a degree, that the fact is intelligible only on
the principle that the cross has caused a partial return to the primitive
disposition.
The Earl of Powis formerly imported some thoroughly domesticated
humped cattle from India, and crossed them with English breeds, which
belong to a distinct species; and his agent remarked to me, without any
question having been asked, how oddly wild the cross-bred animals were.
The European wild boar and the Chinese domesticated pig are almost
certainly specifically distinct: Sir F. Darwin crossed a sow of the latter
breed with a wild Alpine boar which had become extremely tame, but the
young, though having half-domesticated blood in their veins, were
"extremely wild in confinement, and would not eat swill like common
English pigs." Mr. Hewitt, who has had great experience in crossing tame
cock-pheasants with fowls belonging to five breeds, gives as the character
of all "extraordinary wildness;"[105] but I have myself seen one exception to
this rule. Mr. S. J. Salter,[106] who raised a large number of hybrids from a
bantam-hen by Gallus Sonneratii, states that "all were exceedingly wild."
Mr. Waterton[107] bred some wild ducks from eggs hatched under a common

duck, and the young were allowed to cross freely both amongst themselves
and with the tame ducks; they were "half wild and half tame; they came to
the windows to be fed, but still they had a wariness about them quite
remarkable."
On the other hand, mules from the horse and ass are certainly not in the
least wild, yet they are notorious for obstinacy and vice. Mr. Brent, who has
crossed canary-birds with many kinds of finches, has not observed, as he
informs me, that the hybrids were in any way remarkably wild. Hybrids are
often raised between the common and musk duck, and I have been assured
by three persons, who have kept these crossed birds, that they were not
wild; but Mr. Garnett[108] observed that his female hybrids exhibited
"migratory propensities," of which there is not a vestige in the common or
musk duck. No case is known of this latter bird having escaped and become
wild in Europe or Asia, except, according to Pallas, on the Caspian Sea; and
the common domestic duck only occasionally becomes wild in districts
where large lakes and fens abound. Nevertheless, a large number of cases
have been recorded[109] of hybrids from these two ducks, although so few
are reared in comparison with purely-bred birds of either species, having
been shot in a completely wild state. It is improbable that any of these
hybrids could have acquired their wildness from the musk-duck having
paired with a truly wild duck; and this is known not to be the case in North
America; hence we must infer that they have reacquired, through reversion,
their wildness, as well as renewed powers of flight.
These latter facts remind us of the statements, so frequently made by
travellers in all parts of the world, on the degraded state and savage
disposition of crossed races of man. That many excellent and kind-hearted
mulattos have existed no one will dispute; and a more mild and gentle set of
men could hardly be found than the inhabitants of the island of Chiloe, who
consist of Indians commingled with Spaniards in various proportions. On
the other hand, many years ago, long before I had thought of the present
subject, I was struck with the fact that, in South America, men of
complicated descent between Negroes, Indians, and Spaniards, seldom had,
whatever the cause might be, a good expression.[110] Livingstone,—and a
more unimpeachable authority cannot be quoted,—after speaking of a half-
caste man on the Zambesi, described by the Portuguese as a rare monster of

inhumanity, remarks, "It is unaccountable why half-castes, such as he, are
so much more cruel than the Portuguese, but such is undoubtedly the case."
An inhabitant remarked to Livingstone, "God made white men, and God
made black men, but the Devil made half-castes."[111] When two races, both
low in the scale, are crossed, the progeny seems to be eminently bad. Thus
the noble-hearted Humboldt, who felt none of that prejudice against the
inferior races now so current in England, speaks in strong terms of the bad
and savage disposition of Zambos, or half-castes between Indians and
Negroes; and this conclusion has been arrived at by various observers.[112]
From these facts we may perhaps infer that the degraded state of so many
half-castes is in part due to reversion to a primitive and savage condition,
induced by the act of crossing, as well as to the unfavourable moral
conditions under which they generally exist.

Summary on the proximate causes leading to Reversion.—When purely-
bred animals or plants reassume long-lost characters,—when the common
ass, for instance, is born with striped legs, when a pure race of black or
white pigeons throws a slaty-blue bird, or when a cultivated heartsease with
large and rounded flowers produces a seedling with small and elongated
flowers,—we are quite unable to assign any proximate cause. When animals
run wild, the tendency to reversion, which, though it has been greatly
exaggerated, no doubt exists, is sometimes to a certain extent intelligible.
Thus, with feral pigs, exposure to the weather will probably favour the
growth of the bristles, as is known to be the case with the hair of other
domesticated animals, and through correlation the tusks will tend to be
redeveloped. But the reappearance of coloured longitudinal stripes on
young feral pigs cannot be attributed to the direct action of external
conditions. In this case, and in many others, we can only say that changed
habits of life apparently have favoured a tendency, inherent or latent in the
species, to return to the primitive state.
It will be shown in a future chapter that the position of flowers on the
summit of the axis, and the position of seeds within the capsule, sometimes
determine a tendency towards reversion; and this apparently depends on the
amount of sap or nutriment which the flower-buds and seeds receive. The
position, also, of buds, either on branches or on roots, sometimes

determines, as was formerly shown, the transmission of the proper character
of the variety, or its reversion to a former state.
We have seen in the last section that when two races or species are crossed
there is the strongest tendency to the reappearance in the offspring of long-
lost characters, possessed by neither parent nor immediate progenitor. When
two white, or red, or black pigeons, of well-established breeds, are united,
the offspring are almost sure to inherit the same colours; but when
differently-coloured birds are crossed, the opposed forces of inheritance
apparently counteract each other, and the tendency which is inherent in both
parents to produce slaty-blue offspring becomes predominant. So it is in
several other cases. But when, for instance, the ass is crossed with A.
Indicus or with the horse,—animals which have not striped legs,—and the
hybrids have conspicuous stripes on their legs and even on their faces, all
that can be said is, that an inherent tendency to reversion is evolved through
some disturbance in the organisation caused by the act of crossing.
Another form of reversion is far commoner, indeed is almost universal with
the offspring from a cross, namely, to the characters proper to either pure
parent-form. As a general rule, crossed offspring in the first generation are
nearly intermediate between their parents, but the grandchildren and
succeeding generations continually revert, in a greater or lesser degree, to
one or both of their progenitors. Several authors have maintained that
hybrids and mongrels include all the characters of both parents, not fused
together, but merely mingled in different proportions in different parts of
the body; or, as Naudin[113] has expressed it, a hybrid is a living mosaic-
work, in which the eye cannot distinguish the discordant elements, so
completely are they intermingled. We can hardly doubt that, in a certain
sense, this is true, as when we behold in a hybrid the elements of both
species segregating themselves into segments in the same flower or fruit, by
a process of self-attraction or self-affinity; this segregation taking place
either by seminal or by bud-propagation. Naudin further believes that the
segregation of the two specific elements or essences is eminently liable to
occur in the male and female reproductive matter; and he thus explains the
almost universal tendency to reversion in successive hybrid generations.
For this would be the natural result of the union of pollen and ovules, in
both of which the elements of the same species had been segregated by self-
affinity. If, on the other hand, pollen which included the elements of one

species happened to unite with ovules including the elements of the other
species, the intermediate or hybrid state would still be retained, and there
would be no reversion. But it would, as I suspect, be more correct to say
that the elements of both parent-species exist in every hybrid in a double
state, namely, blended together and completely separate. How this is
possible, and what the term specific essence or element may be supposed to
express, I shall attempt to show in the hypothetical chapter on pangenesis.
But Naudin's view, as propounded by him, is not applicable to the
reappearance of characters lost long ago by variation; and it is hardly
applicable to races or species which, after having been crossed at some
former period with a distinct form, and having since lost all traces of the
cross, nevertheless occasionally yield an individual which reverts (as in the
case of the great-great-grandchild of the pointer Sappho) to the crossing
form. The most simple case of reversion, namely, of a hybrid or mongrel to
its grandparents, is connected by an almost perfect series with the extreme
case of a purely-bred race recovering characters which had been lost during
many ages; and we are thus led to infer that all the cases must be related by
some common bond.
Gärtner believed that only those hybrid plants which are highly sterile
exhibit any tendency to reversion to their parent-forms. It is rash to doubt so
good an observer, but this conclusion must I think be an error; and it may
perhaps be accounted for by the nature of the genera observed by him, for
he admits that the tendency differs in different genera. The statement is also
directly contradicted by Naudin's observations, and by the notorious fact
that perfectly fertile mongrels exhibit the tendency in a high degree,—even
in a higher degree, according to Gärtner himself, than hybrids.[114]
Gärtner further states that reversions rarely occur with hybrid plants raised
from species which have not been cultivated, whilst, with those which have
been long cultivated, they are of frequent occurrence. This conclusion
explains a curious discrepancy: Max Wichura,[115] who worked exclusively
on willows, which had not been subjected to culture, never saw an instance
of reversion; and he goes so far as to suspect that the careful Gärtner had
not sufficiently protected his hybrids from the pollen of the parent-species:
Naudin, on the other hand, who chiefly experimented on cucurbitaceous
and other cultivated plants, insists more strenuously than any other author

on the tendency to reversion in all hybrids. The conclusion that the
condition of the parent-species, as affected by culture, is one of the
proximate causes leading to reversion, agrees fairly well with the converse
case of domesticated animals and cultivated plants being liable to reversion
when they become feral; for in both cases the organisation or constitution
must be disturbed, though in a very different way.
Finally, we have seen that characters often reappear in purely-bred races
without our being able to assign any proximate cause; but when they
become feral this is either indirectly or directly induced by the change in
their conditions of life. With crossed breeds, the act of crossing in itself
certainly leads to the recovery of long-lost characters, as well as of those
derived from either parent-form. Changed conditions, consequent on
cultivation, and the relative position of buds, flowers, and seeds on the
plant, all apparently aid in giving this same tendency. Reversion may occur
either through seminal or bud generation, generally at birth, but sometimes
only with an advance of age. Segments or portions of the individual may
alone be thus affected. That a being should be born resembling in certain
characters an ancestor removed by two or three, and in some cases by
hundreds or even thousands of generations, is assuredly a wonderful fact. In
these cases the child is commonly said to inherit such characters directly
from its grandparents or more remote ancestors. But this view is hardly
conceivable. If, however, we suppose that every character is derived
exclusively from the father or mother, but that many characters lie latent in
both parents during a long succession of generations, the foregoing facts are
intelligible. In what manner characters may be conceived to lie latent, will
be considered in a future chapter to which I have lately alluded.

Latent Characters.—But I must explain what is meant by characters lying
latent. The most obvious illustration is afforded by secondary sexual
characters. In every female all the secondary male characters, and in every
male all the secondary female characters, apparently exist in a latent state,
ready to be evolved under certain conditions. It is well known that a large
number of female birds, such as fowls, various pheasants, partridges,
peahens, ducks, &c., when old or diseased, or when operated on, partly
assume the secondary male characters of their species. In the case of the
hen-pheasant this has been observed to occur far more frequently during

certain seasons than during others.[116] A duck ten years old has been known
to assume both the perfect winter and summer plumage of the drake.[117]
Waterton[118] gives a curious case of a hen which had ceased laying, and
had assumed the plumage, voice, spurs, and warlike disposition of the cock;
when opposed to an enemy she would erect her hackles and show fight.
Thus every character, even to the instinct and manner of fighting, must have
lain dormant in this hen as long as her ovaria continued to act. The females
of two kinds of deer, when old, have been known to acquire horns; and, as
Hunter has remarked, we see something of an analogous nature in the
human species.
On the other hand, with male animals, it is notorious that the secondary
sexual characters are more or less completely lost when they are subjected
to castration. Thus, if the operation be performed on a young cock, he
never, as Yarrell states, crows again; the comb, wattles, and spurs do not
grow to their full size, and the hackles assume an intermediate appearance
between true hackles and the feathers of the hen. Cases are recorded of
confinement alone causing analogous results. But characters properly
confined to the female are likewise acquired; the capon takes to sitting on
eggs, and will bring up chickens; and what is more curious, the utterly
sterile male hybrids from the pheasant and the fowl act in the same manner,
"their delight being to watch when the hens leave their nests, and to take on
themselves the office of a sitter."[119] That admirable observer Réaumur[120]
asserts that a cock, by being long confined in solitude and darkness, can be
taught to take charge of young chickens; he then utters a peculiar cry, and
retains during his whole life this newly acquired maternal instinct. The
many well-ascertained cases of various male mammals giving milk, show
that their rudimentary mammary glands retain this capacity in a latent
condition.
We thus see that in many, probably in all cases, the secondary characters of
each sex lie dormant or latent in the opposite sex, ready to be evolved under
peculiar circumstances. We can thus understand how, for instance, it is
possible for a good milking cow to transmit her good qualities through her
male offspring to future generations; for we may confidently believe that
these qualities are present, though latent, in the males of each generation.
So it is with the game-cock, who can transmit his superiority in courage and

vigour through his female to his male offspring; and with man it is known
[121] that diseases, such as hydrocele, necessarily confined to the male sex,

can be transmitted through the female to the grandson. Such cases as these
offer, as was remarked at the commencement of this chapter, the simplest
possible examples of reversion; and they are intelligible on the belief that
characters common to the grandparent and grandchild of the same sex are
present, though latent, in the intermediate parent of the opposite sex.
The subject of latent characters is so important, as we shall see in a future
chapter, that I will give another illustration. Many animals have the right
and left sides of their body unequally developed: this is well known to be
the case with flat-fish, in which the one side differs in thickness and colour,
and in the shape of the fins, from the other; and during the growth of the
young fish one eye actually travels, as shown by Steenstrup, from the lower
to the upper surface.[122] In most flat-fishes the left is the blind side, but in
some it is the right; though in both cases "wrong fishes," which are
developed in a reversed manner to what is usual, occasionally occur, and in
Platessa flesus the right or left side is indifferently developed, the one as
often as the other. With gasteropods or shell-fish, the right and left sides are
extremely unequal; the far greater number of species are dextral, with rare
and occasional reversals of development, and some few are normally
sinistral; but certain species of Bulimus, and, many Achatinellæ,[123] are as
often sinistral as dextral. I will give an analogous case in the great
Articulate kingdom: the two sides of Verruca[124] are so wonderfully unlike,
that without careful dissection it is extremely difficult to recognise the
corresponding parts on the opposite sides of the body; yet it is apparently a
mere matter of chance whether it be the right or the left side that undergoes
so singular an amount of change. One plant is known to me[125] in which
the flower, according as it stands on the one or other side of the spike, is
unequally developed. In all the foregoing cases the two sides of the animal
are perfectly symmetrical at an early period of growth. Now, whenever a
species is as liable to be unequally developed on the one as on the other
side, we may infer that the capacity for such development is present, though
latent, in the undeveloped side. And as a reversal of development
occasionally occurs in animals of many kinds, this latent capacity is
probably very common.

The best yet simplest instances of characters lying dormant are, perhaps,
those previously given, in which chickens and young pigeons, raised from a
cross between differently coloured birds, are at first of one colour, but in a
year or two acquire feathers of the colour of the other parent; for in this case
the tendency to a change of plumage is clearly latent in the young bird. So it
is with hornless breeds of cattle, some of which acquire, as they grow old,
small horns. Purely bred black and white bantams, and some other fowls,
occasionally assume, with advancing years, the red feathers of the parent-
species. I will here add a somewhat different case, as it connects in a
striking manner latent characters of two classes. Mr. Hewitt[126] possessed
an excellent Sebright gold-laced hen bantam, which, as she became old,
grew diseased in her ovaria, and assumed male characters. In this breed the
males resemble the females in all respects except in their combs, wattles,
spurs, and instincts; hence it might have been expected that the diseased hen
would have assumed only those masculine characters which are proper to
the breed, but she acquired, in addition, well-arched tail sickle-feathers
quite a foot in length, saddle-feathers on the loins, and hackles on the neck,
—ornaments which, as Mr. Hewitt remarks, "would be held as abominable
in this breed." The Sebright bantam is known[127] to have originated about
the year 1800 from a cross between a common bantam and a Polish fowl,
recrossed by a hen-tailed bantam, and carefully selected; hence there can
hardly be a doubt that the sickle-feathers and hackles which appeared in the
old hen were derived from the Polish fowl or common bantam; and we thus
see that not only certain masculine characters proper to the Sebright
bantam, but other masculine characters derived from the first progenitors of
the breed, removed by a period of above sixty years, were lying latent in
this hen-bird, ready to be evolved as soon as her ovaria became diseased.
From these several facts it must be admitted that certain characters,
capacities, and instincts may lie latent in an individual, and even in a
succession of individuals, without our being able to detect the least signs of
their presence. We have already seen that the transmission of a character
from the grandparent to the grandchild, with its apparent omission in the
intermediate parent of the opposite sex, becomes simple on this view. When
fowls, pigeons, or cattle of different colours are crossed, and their offspring
change colour as they grow old, or when the crossed turbit acquired the
characteristic frill after its third moult, or when purely-bred bantams

partially assume the red plumage of their prototype, we cannot doubt that
these qualities were from the first present, though latent, in the individual
animal, like the characters of a moth in the caterpillar. Now, if these animals
had produced offspring before they had acquired with advancing age their
new characters, nothing is more probable than that they would have
transmitted them to some of their offspring, which in this case would in
appearance have received such characters from their grandparents or more
distant progenitors. We should then have had a case of reversion, that is, of
the reappearance in the child of an ancestral character, actually present,
though during youth completely latent, in the parent; and this we may safely
conclude is what occurs with reversions of all kinds to progenitors however
remote.
This view of the latency in each generation of all the characters which
appear through reversion, is also supported by their actual presence in some
cases during early youth alone, or by their more frequent appearance and
greater distinctness at this age than during maturity. We have seen that this
is often the case with the stripes on the legs and faces of the several species
of the horse-genus. The Himalayan rabbit, when crossed, sometimes
produces offspring which revert to the parent silver-grey breed, and we
have seen that in purely bred animals pale-grey fur occasionally reappears
during early youth. Black cats, we may feel assured, would occasionally
produce by reversion tabbies; and on young black kittens, with a
pedigree[128] known to have been long pure, faint traces of stripes may
almost always be seen which afterwards disappear. Hornless Suffolk cattle
occasionally produce by reversion horned animals; and Youatt[129] asserts
that even in hornless individuals "the rudiment of a horn may be often felt
at an early age."
No doubt it appears at first sight in the highest degree improbable that in
every horse of every generation there should be a latent capacity and
tendency to produce stripes, though these may not appear once in a
thousand generations; that in every white, black, or other coloured pigeon,
which may have transmitted its proper colour during centuries, there should
be a latent capacity in the plumage to become blue and to be marked with
certain characteristic bars; that in every child in a six-fingered family there
should be the capacity for the production of an additional digit; and so in
other cases. Nevertheless there is no more inherent improbability in this

being the case than in a useless and rudimentary organ, or even in only a
tendency to the production of a rudimentary organ, being inherited during
millions of generations, as is well known to occur with a multitude of
organic beings. There is no more inherent improbability in each domestic
pig, during a thousand generations, retaining the capacity and tendency to
develop great tusks under fitting conditions, than in the young calf having
retained for an indefinite number of generations rudimentary incisor teeth,
which never protrude through the gums.
I shall give at the end of the next chapter a summary of the three preceding
chapters; but as isolated and striking cases of reversion have here been
chiefly insisted on, I wish to guard the reader against supposing that
reversion is due to some rare or accidental combination of circumstances.
When a character, lost during hundreds of generations, suddenly reappears,
no doubt some such combination must occur; but reversions may be
constantly observed, at least to the immediately preceding generations, in
the offspring of most unions. This has been universally recognised in the
case of hybrids and mongrels, but it has been recognised simply from the
difference between the united forms rendering the resemblance of the
offspring to their grandparents or more remote progenitors of easy
detection. Reversion is likewise almost invariably the rule, as Mr. Sedgwick
has shown, with certain diseases. Hence we must conclude that a tendency
to this peculiar form of transmission is an integral part of the general law of
inheritance.

Monstrosities.—A large number of monstrous growths and of lesser
anomalies are admitted by every one to be due to an arrest of development,
that is to the persistence of an embryonic condition. If every horse or ass
had striped legs whilst young, the stripes which occasionally appear on
these animals when adult would have to be considered as due to the
anomalous retention of an early character, and not as due to reversion. Now,
the leg-stripes in the horse-genus, and some other characters in analogous
cases, are apt to occur during early youth and then to disappear; thus the
persistence of early characters and reversion are brought into close
connexion.

But many monstrosities can hardly be considered as the result of an arrest
of development; for parts of which no trace can be detected in the embryo,
but which occur in other members of the same class of animals or plants,
occasionally appear, and these may probably with truth be attributed to
reversion. For instance: supernumerary mammæ, capable of secreting milk,
are not extremely rare in women; and as many as five have been observed.
When four are developed, they are generally arranged symmetrically on
each side of the chest; and in one instance a woman (the daughter of
another with supernumerary mammæ) had one mamma, which yielded
milk, developed in the inguinal region. This latter case, when we remember
the position of the mammæ in some of the lower animals on both the chest
and inguinal region, is highly remarkable, and leads to the belief that in all
cases the additional mammæ in woman are due to reversion. The facts
given in the last chapter on the tendency in supernumerary digits to
regrowth after amputation, indicate their relation to the digits of the lower
vertebrate animals, and lead to the suspicion that their appearance may in
some manner be connected with reversion. But I shall have to recur, in the
chapter on pangenesis, to the abnormal multiplication of organs, and
likewise to their occasional transposition. The occasional development in
man of the coccygeal vertebræ into a short and free tail, though it thus
becomes in one sense more perfectly developed, may at the same time be
considered as an arrest of development, and as a case of reversion. The
greater frequency of a monstrous kind of proboscis in the pig than in any
other mammal, considering the position of the pig in the mammalian series,
has likewise been attributed, perhaps truly, to reversion.[130]

When flowers which are properly irregular in structure become regular
or peloric, the change is generally looked at by botanists as a return to
the primitive state. But Dr. Maxwell Masters,[131] who has ably
discussed this subject, remarks that when, for instance, all the sepals of
a Tropæolum become green and of the same shape, instead of being
coloured with one alone prolonged into a spur, or when all the petals of
a Linaria become simple and regular, such cases may be due merely to
an arrest of development; for in these flowers all the organs during
their earliest condition are symmetrical, and, if arrested at this stage of
growth, they would not become irregular. If, moreover, the arrest were
to take place at a still earlier period of development, the result would

be a simple tuft of green leaves; and no one probably would call this a
case of reversion. Dr. Masters designates the cases first alluded to as
regular peloria; and others, in which all the corresponding parts assume
a similar form of irregularity, as when all the petals in a Linaria
become spurred, as irregular peloria. We have no right to attribute
these latter cases to reversion, until it can be shown to be probable that
the parent-form, for instance, of the genus Linaria had had all its petals
spurred; for a change of this nature might result from the spreading of
an anomalous structure, in accordance with the law, to be discussed in
a future chapter, of homologous parts tending to vary in the same
manner. But as both forms of peloria frequently occur on the same
individual plant of the Linaria,[132] they probably stand in some close
relation to each other. On the doctrine that peloria is simply the result
of an arrest of development, it is difficult to understand how an organ
arrested at a very early period of growth should acquire its full
functional perfection;—how a petal, supposed to be thus arrested,
should acquire its brilliant colours, and serve as an envelope to the
flower, or a stamen produce efficient pollen; yet this occurs with many
peloric flowers. That pelorism is not due to mere chance variability,
but either to an arrest of development or to reversion, we may infer
from an observation made by Ch. Morren,[133] namely, that families
which have irregular flowers often "return by these monstrous growths
to their regular form; whilst we never see a regular flower realise the
structure of an irregular one."
Some flowers have almost certainly become more or less completely
peloric through reversion. Corydalis tuberosa properly has one of its
two nectaries colourless, destitute of nectar, only half the size of the
other, and therefore, to a certain extent, in a rudimentary state; the
pistil is curved towards the perfect nectary, and the hood, formed of the
inner petals, slips off the pistil and stamens in one direction alone, so
that, when a bee sucks the perfect nectary, the stigma and stamens are
exposed and rubbed against the insect's body. In several closely allied
genera, as in Dielytra, &c., there are two perfect nectaries, the pistil is
straight, and the hood slips off on either side, according as the bee
sucks either nectary. Now, I have examined several flowers of
Corydalis tuberosa, in which both nectaries were equally developed

and contained nectar; in this we see only the redevelopment of a
partially aborted organ; but with this redevelopment the pistil becomes
straight, and the hood slips off in either direction; so that these flowers
have acquired the perfect structure, so well adapted for insect agency,
of Dielytra and its allies. We cannot attribute these coadapted
modifications to chance, or to correlated variability; we must attribute
them to reversion to a primordial condition of the species.
The peloric flowers of Pelargonium have their five petals in all
respects alike, and there is no nectary; so that they resemble the
symmetrical flowers of the closely allied Geranium-genus; but the
alternate stamens are also sometimes destitute of anthers, the shortened
filaments being left as rudiments, and in this respect they resemble the
symmetrical flowers of the closely allied genus, Erodium. Hence we
are led to look at the peloric flowers of Pelargonium as having
probably reverted to the state of some primordial form, the progenitor
of the three closely related genera of Pelargonium, Geranium, and
Erodium.
In the peloric form of Antirrhinum majus, appropriately called the
"Wonder," the tubular and elongated flowers differ wonderfully from
those of the common snapdragon; the calyx and the mouth of the
corolla consist of six equal lobes, and include six equal instead of four
unequal stamens. One of the two additional stamens is manifestly
formed by the development of a microscopically minute papilla, which
may be found at the base of the upper lip of the flower in all common
snapdragons, at least in nineteen plants examined by me. That this
papilla is a rudiment of a stamen was well shown by its various
degrees of development in crossed plants between the common and
peloric Antirrhinum. Again, a peloric Galeobdolon luteum, growing in
my garden, had five equal petals, all striped like the ordinary lower lip,
and included five equal instead of four unequal stamens; but Mr. R.
Keeley, who sent me this plant, informs me that the flowers vary
greatly, having from four to six lobes to the corolla, and from three to
six stamens.[134] Now, as the members of the two great families to
which the Antirrhinum and Galeobdolon belong are properly
pentamerous, with some of the parts confluent and others suppressed,
we ought not to look at the sixth stamen and the sixth lobe to the

corolla in either case as due to reversion, any more than the additional
petals in double flowers in these same two families. But the case is
different with the fifth stamen in the peloric Antirrhinum, which is
produced by the redevelopment of a rudiment always present, and
which probably reveals to us the state of the flower, as far as the
stamens are concerned, at some ancient epoch. It is also difficult to
believe that the other four stamens and the petals, after an arrest of
development at a very early embryonic age, would have come to full
perfection in colour, structure, and function, unless these organs had at
some former period normally passed through a similar course of
growth. Hence it appears to me probable that the progenitor of the
genus Antirrhinum must at some remote epoch have included five
stamens and borne flowers in some degree resembling those now
produced by the peloric form.
Lastly, I may add that many instances have been recorded of flowers,
not generally ranked as peloric, in which certain organs, normally few
in number, have been abnormally augmented. As such an increase of
parts cannot be looked at as an arrest of development, nor as due to the
redevelopment of rudiments, for no rudiments are present, and as these
additional parts bring the plant into closer relationship with its natural
allies, they ought probably to be viewed as reversions to a primordial
condition.

These several facts show us in an interesting manner how intimately certain
abnormal states are connected together; namely, arrests of development
causing parts to become rudimentary or to be wholly suppressed,—the
redevelopment of parts at present in a more or less rudimentary condition,
—the reappearance of organs of which not a vestige can now be detected,—
and to these may be added, in the case of animals, the presence during
youth, and subsequent disappearance, of certain characters which
occasionally are retained throughout life. Some naturalists look at all such
abnormal structures as a return to the ideal state of the group to which the
affected being belongs; but it is difficult to conceive what is meant to be
conveyed by this expression. Other naturalists maintain, with greater
probability and distinctness of view, that the common bond of connection
between the several foregoing cases is an actual, though partial, return to
the structure of the ancient progenitor of the group. If this view be correct,

we must believe that a vast number of characters, capable of evolution, lie
hidden in every organic being. But it would be a mistake to suppose that the
number is equally great in all beings. We know, for instance, that plants of
many orders occasionally become peloric; but many more cases have been
observed in the Labiatæ and Scrophulariaceæ than in any other order; and
in one genus of the Scrophulariaceæ, namely Linaria, no less than thirteen
species have been described in a peloric condition.[135] On this view of the
nature of peloric flowers, and bearing in mind what has been said with
respect to certain monstrosities in the animal kingdom, we must conclude
that the progenitors of most plants and animals, though widely different in
structure, have left an impression capable of redevelopment on the germs of
their descendants.
The fertilised germ of one of the higher animals, subjected as it is to so vast
a series of changes from the germinal cell to old age,—incessantly agitated
by what Quatrefages well calls the tourbillon vital,—is perhaps the most
wonderful object in nature. It is probable that hardly a change of any kind
affects either parent, without some mark being left on the germ. But on the
doctrine of reversion, as given in this chapter, the germ becomes a far more
marvellous object, for, besides the visible changes to which it is subjected,
we must believe that it is crowded with invisible characters, proper to both
sexes, to both the right and left side of the body, and to a long line of male
and female ancestors separated by hundreds or even thousands of
generations from the present time; and these characters, like those written
on paper with invisible ink, all lie ready to be evolved under certain known
or unknown conditions.

CHAPTER XIV.

INHERITANCE continued—FIXEDNESS OF CHARACTER—
PREPOTENCY—SEXUAL LIMITATION—CORRESPONDENCE OF
AGE.

FIXEDNESS OF CHARACTER APPARENTLY NOT DUE TO ANTIQUITY OF
INHERITANCE—PREPOTENCY OF TRANSMISSION IN INDIVIDUALS OF THE
SAME FAMILY, IN CROSSED BREEDS AND SPECIES; OFTEN STRONGER IN ONE

SEX THAN THE OTHER; SOMETIMES DUE TO THE SAME CHARACTER BEING
PRESENT AND VISIBLE IN ONE BREED AND LATENT IN THE OTHER—
INHERITANCE AS LIMITED BY SEX—NEWLY-ACQUIRED CHARACTERS IN OUR
DOMESTICATED ANIMALS OFTEN TRANSMITTED BY ONE SEX ALONE,
SOMETIMES LOST BY ONE SEX ALONE—INHERITANCE AT CORRESPONDING
PERIODS OF LIFE—THE IMPORTANCE OF THE PRINCIPLE WITH RESPECT TO
EMBRYOLOGY; AS EXHIBITED IN DOMESTICATED ANIMALS; AS EXHIBITED IN
THE APPEARANCE AND DISAPPEARANCE OF INHERITED DISEASES; SOMETIMES
SUPERVENING EARLIER IN THE CHILD THAN IN THE PARENT—SUMMARY OF
THE THREE PRECEDING CHAPTERS.

In the two last chapters the nature and force of Inheritance, the
circumstances which interfere with its power, and the tendency to
Reversion, with its many remarkable contingencies, were discussed. In the
present chapter some other related phenomena will be treated of, as fully as
my materials permit.

Fixedness of Character.
It is a general belief amongst breeders that the longer any character has
been transmitted by a breed, the more firmly it will continue to be
transmitted. I do not wish to dispute the truth of the proposition, that
inheritance gains strength simply through long continuance, but I doubt
whether it can be proved. In one sense the proposition is little better than a
truism; if any character has remained constant during many generations, it
will obviously be little likely, the conditions of life remaining the same, to
vary during the next generation. So, again, in improving a breed, if care be
taken for a length of time to exclude all inferior individuals, the breed will
obviously tend to become truer, as it will not have been crossed during
many generations by an inferior animal. We have previously seen, but
without being able to assign any cause, that, when a new character appears,
it is occasionally from the first well fixed, or fluctuates much, or wholly
fails to be transmitted. So it is with the aggregate of slight differences which
characterise a new variety, for some propagate their kind from the first
much truer than others. Even with plants multiplied by bulbs, layers, &c.,
which may in one sense be said to form parts of the same individual, it is
well known that certain varieties retain and transmit through successive
bud-generations their newly-acquired characters more truly than others. In

none of these, nor in the following cases, does there appear to be any
relation between the force with which a character is transmissible and the
length of time during which it has already been transmitted. Some varieties,
such as white and yellow hyacinths and white sweet-peas, transmit their
colours more faithfully than do the varieties which have retained their
natural colour. In the Irish family, mentioned in the twelfth chapter, the
peculiar tortoiseshell-like colouring of the eyes was transmitted far more
faithfully than any ordinary colour. Ancon and Mauchamp sheep and niata
cattle, which are all comparatively modern breeds, exhibit remarkably
strong powers of inheritance. Many similar cases could be adduced.
As all domesticated animals and cultivated plants have varied, and yet are
descended from aboriginally wild forms, which no doubt had retained the
same character from an immensely remote epoch, we see that scarcely any
degree of antiquity ensures a character being transmitted perfectly true. In
this case, however, it may be said that changed conditions of life induce
certain modifications, and not that the power of inheritance fails; but in
every case of failure, some cause, either internal or external, must interfere.
It will generally be found that the parts in our domesticated productions
which have varied, or which still continue to vary,—that is, which fail to
retain their primordial state,—are the same with the parts which differ in the
natural species of the same genus. As, on the theory of descent with
modification, the species of the same genus have been modified since they
branched off from a common progenitor, it follows that the characters by
which they differ from each other have varied whilst other parts of the
organisation have remained unchanged; and it might be argued that these
same characters now vary under domestication, or fail to be inherited,
owing to their lesser antiquity. But we must believe structures, which have
already varied, would be more liable to go on varying, rather than structures
which during an immense lapse of time have remained unaltered; and this
variation is probably the result of certain relations between the conditions of
life and the organisation, quite independently of the greater or less antiquity
of each particular character.
Fixedness of character, or the strength of inheritance, has often been judged
of by the preponderance of certain characters in the crossed offspring
between distinct races; but prepotency of transmission here comes into play,
and this, as we shall immediately see, is a very different consideration from

the strength or weakness of inheritance. It has often been observed[136] that
breeds of animals inhabiting wild and mountainous countries cannot be
permanently modified by our improved breeds; and as these latter are of
modern origin, it has been thought that the greater antiquity of the wilder
breeds has been the cause of their resistance to improvement by crossing;
but it is more probably due to their structure and constitution being better
adapted to the surrounding conditions. When plants are first subjected to
culture, it has been found that, during several generations, they transmit
their characters truly, that is, do not vary, and this has been attributed to
ancient characters being strongly inherited; but it may with equal or greater
probability be consequent on changed conditions of life requiring a long
time for their accumulative action. Notwithstanding these considerations, it
would perhaps be rash to deny that characters become more strongly fixed
the longer they are transmitted; but I believe that the proposition resolves
itself into this,—that all characters of all kinds, whether new or old, tend to
be inherited, and that those which have already withstood all counteracting
influences and been truly transmitted, will, as a general rule, continue to
withstand them, and consequently be faithfully inherited.

Prepotency in the Transmission of Character.
When individuals distinct enough to be recognised, but of the same family,
or when two well-marked races, or two species, are crossed, the usual
result, as stated in the previous chapter, is, that the offspring in the first
generation are intermediate between their parents, or resemble one parent in
one part and the other parent in another part. But this is by no means the
invariable rule; for in many cases it is found that certain individuals, races,
and species are prepotent in transmitting their likeness. This subject has
been ably discussed by Prosper Lucas,[137] but is rendered extremely
complicated by the prepotency sometimes running equally in both sexes,
and sometimes more strongly in one sex than in the other; it is likewise
complicated by the presence of secondary sexual characters, which render
the comparison of mongrels with their parent-breeds difficult.
It would appear that in certain families some one ancestor, and after him
others in the same family, must have had great power in transmitting their
likeness through the male line; for we cannot otherwise understand how the
same features should so often be transmitted after marriages with various

females, as has been the case with the Austrian Emperors, and as, according
to Niebuhr, formerly occurred in certain Roman families with their mental
qualities.[138] The famous bull Favourite is believed[139] to have had a
prepotent influence on the shorthorn race. It has also been observed[140]
with English race-horses that certain mares have generally transmitted their
own character, whilst other mares of equally pure blood have allowed the
character of the sire to prevail.

The truth of the principle of prepotency comes out more clearly when
certain races are crossed. The improved Shorthorns, notwithstanding
that the breed is comparatively modern, are generally acknowledged to
possess great power in impressing their likeness on all other breeds;
and it is chiefly in consequence of this power that they are so highly
valued for exportation.[141] Godine has given a curious case of a ram of
a goat-like breed of sheep from the Cape of Good Hope, which
produced offspring hardly to be distinguished from himself, when
crossed with ewes of twelve other breeds. But two of these half-bred
ewes, when put to a merino ram, produced lambs closely resembling
the merino breed. Girou de Buzareingues[142] found that of two races
of French sheep the ewes of one, when crossed during successive
generations with merino rams, yielded up their character far sooner
than the ewes of the other race. Sturm and Girou have given analogous
cases with other breeds of sheep and with cattle, the prepotency
running in these cases through the male side; but I was assured on
good authority in South America, that when niata cattle are crossed
with common cattle, though the niata breed is prepotent whether males
or females are used, yet that the prepotency is strongest through the
female line. The Manx cat is tailless and has long hind legs; Dr. Wilson
crossed a male Manx with common cats, and, out of twenty-three
kittens, seventeen were destitute of tails; but when the female Manx
was crossed by common male cats all the kittens had tails, though they
were generally short and imperfect.[143]
In making reciprocal crosses between pouter and fantail pigeons, the
pouter-race seemed to be prepotent through both sexes over the fantail.
But this is probably due to weak power in the fantail rather than to any
unusually strong power in the pouter, for I have observed that barbs

also preponderated over fantails. This weakness of transmission in the
fantail, though the breed is an ancient one, is said[144] to be general;
but I have observed one exception to the rule, namely, in a cross
between a fantail and laugher. The most curious instance known to me
of weak power in both sexes is in the trumpeter pigeon. This breed has
been well known for at least 130 years: it breeds perfectly true, as I
have been assured by those who have long kept many birds: it is
characterised by a peculiar tuft of feathers over the beak, by a crest on
the head, by a most peculiar coo quite unlike that of any other breed,
and by much-feathered feet. I have crossed both sexes with turbits of
two sub-breeds, with almond tumblers, spots, and runts, and reared
many mongrels and recrossed them; and though the crest on the head
and feathered feet were inherited (as is generally the case with most
breeds), I have never seen a vestige of the tuft over the beak or heard
the peculiar coo. Boitard and Corbié[145] assert that this is the
invariable result of crossing trumpeters with any other breed:
Neumeister,[146] however, states that in Germany mongrels have been
obtained, though very rarely, which were furnished with the tuft and
would trumpet: but a pair of these mongrels with a tuft, which I
imported, never trumpeted. Mr. Brent states[147] that the crossed
offspring of a trumpeter were crossed with trumpeters for three
generations, by which time the mongrels had 7-8ths of this blood in
their veins, yet the tuft over the beak did not appear. At the fourth
generation the tuft appeared, but the birds, though now having 15-
16ths trumpeter's blood, still did not trumpet. This case well shows the
wide difference between inheritance and prepotency; for here we have
a well-established old race which transmits it characters faithfully, but
which, when crossed with any other race, has the feeblest power of
transmitting its two chief characteristic qualities.
I will give one other instance with fowls and pigeons of weakness and
strength in the transmission of the same character to their crossed
offspring. The Silk-fowl breeds true, and there is reason to believe is a
very ancient race; but when I reared a large number of mongrels from a
Silk-hen by a Spanish cock, not one exhibited even a trace of the so-
called silkiness. Mr. Hewitt also asserts that in no instance are the silky
feathers transmitted by this breed when crossed with any other variety.

But three birds out of many raised by Mr. Orton from a cross between
a silk-cock and a bantam-hen, had silky feathers.[148] So that it is
certain that this breed very seldom has the power of transmitting its
peculiar plumage to its crossed progeny. On the other hand, there is a
silk sub-variety of the fantail pigeon, which has its feathers in nearly
the same state as in the Silk-fowl: now we have already seen that
fantails, when crossed, possess singularly weak power in transmitting
their general qualities; but the silk sub-variety when crossed with any
other small-sized race invariably transmits its silky feathers![149]
The law of prepotency comes into action when species are crossed, as
with races and individuals. Gärtner has unequivocally shown[150] that
this is the case with plants. To give one instance: when Nicotiana
paniculata and vincæflora are crossed, the character of N. paniculata is
almost completely lost in the hybrid; but if N. quadrivalvis be crossed
with N. vincæflora, this later species, which was before so prepotent,
now in its turn almost disappears under the power of N. quadrivalvis. It
is remarkable that the prepotency of one species over another in
transmission is quite independent, as shown by Gärtner, of the greater
or less facility with which the one fertilises the other.
With animals, the jackal is prepotent over the dog, as is stated by
Flourens who made many crosses between these animals; and this was
likewise the case with a hybrid which I once saw between a jackal and
terrier. I cannot doubt, from the observations of Colin and others, that
the ass is prepotent over the horse; the prepotency in this instance
running more strongly through the male than through the female ass;
so that the mule resembles the ass more closely than does the hinny.
[151] The male pheasant, judging from Mr. Hewitt's descriptions,[152]

and from the hybrids which I have seen, preponderates over the
domestic fowl; but the latter, as far as colour is concerned, has
considerable power of transmission, for hybrids raised from five
differently coloured hens differed greatly in plumage. I formerly
examined some curious hybrids in the Zoological Gardens, between
the Penguin variety of the common duck and the Egyptian goose
(Tadorna Ægyptiaca); and although I will not assert that the

domesticated variety preponderated over the natural species, yet it had
strongly impressed its unnatural upright figure on these hybrids.
I am aware that such cases as the foregoing have been ascribed by
various authors, not to one species, race, or individual being prepotent
over the other in impressing it character on its crossed offspring, but to
such rules as that the father influences the external characters and the
mother the internal or vital organs. But the great diversity of the rules
given by various authors almost proves their falseness. Dr. Prosper
Lucas has fully discussed this point, and has shown[153] that none of
the rules (and I could add others to those quoted by him) apply to all
animals. Similar rules have been enounced for plants, and have been
proved by Gärtner[154] to be all erroneous. If we confine our view to
the domesticated races of a single species, or perhaps even to the
species of the same genus, some such rules may hold good; for
instance, it seems that in reciprocally crossing various breeds of fowls
the male generally gives colour;[155] but conspicuous exceptions have
passed under my own eyes. In sheep it seems that the ram usually
gives its peculiar horns and fleece to its crossed offspring, and the bull
the presence or absence of horns.
In the following chapter on Crossing I shall have occasion to show that
certain characters are rarely or never blended by crossing, but are
transmitted in an unmodified state from either parent-form; I refer to
this fact here because it is sometimes accompanied on the one side by
prepotency, which thus acquires the false appearance of unusual
strength. In the same chapter I shall show that the rate at which a
species or breed absorbs and obliterates another by repeated crosses,
depends in chief part on prepotency in transmission.

In conclusion, some of the cases above given,—for instance, that of the
trumpeter pigeon,—prove that there is a wide difference between mere
inheritance and prepotency. This latter power seems to us, in our ignorance,
to act in most cases quite capriciously. The very same character, even
though it be an abnormal or monstrous one, such as silky feathers, may be
transmitted by different species, when crossed, either with prepotent force
or singular feebleness. It is obvious, that a purely-bred form of either sex, in
all cases in which prepotency does not run more strongly in one sex than

the other, will transmit its character with prepotent force over a mongrelized
and already variable form.[156] From several of the above-given cases we
may conclude that mere antiquity of character does not by any means
necessarily make it prepotent. In some cases prepotency apparently depends
on the same character being present and visible in one of the two breeds
which are crossed, and latent or invisible in the other breed; and in this case
it is natural that the character which is potentially present in both should be
prepotent. Thus, we have reason to believe that there is a latent tendency in
all horses to be dun-coloured and striped; and when a horse of this kind is
crossed with one of any other colour, it is said that the offspring are almost
sure to be striped. Sheep have a similar latent tendency to become dark-
coloured, and we have seen with what prepotent force a ram with a few
black spots, when crossed with sheep of various breeds, coloured its
offspring. All pigeons have a latent tendency to become slaty-blue, with
certain characteristic marks, and it is known that, when a bird thus coloured
is crossed with one of any other colour, it is most difficult afterwards to
eradicate the blue tint. A nearly parallel case is offered by those black
bantams which, as they grow old, develop a latent tendency to acquire red
feathers. But there are exceptions to the rule: hornless breeds of cattle
possess a latent capacity to reproduce horns, yet when crossed with horned
breeds they do not invariably produce offspring bearing horns.
We meet with analogous cases with plants. Striped flowers, though they can
be propagated truly by seed, have a latent tendency to become uniformly
coloured, but when once crossed by a uniformly coloured variety, they ever
afterwards fail to produce striped seedlings.[157] Another case is in some
respects more curious: plants bearing peloric or regular flowers have so
strong a latent tendency to reproduce their normally irregular flowers, that
this often occurs by buds when a plant is transplanted into poorer or richer
soil.[158] Now I crossed the peloric snapdragon (Antirrhinum majus),
described in the last chapter, with pollen of the common form; and the
latter, reciprocally, with peloric pollen. I thus raised two great beds of
seedlings, and not one was peloric. Naudin[159] obtained the same result
from crossing a peloric Linaria with the common form. I carefully
examined the flowers of ninety plants of the crossed Antirrhinum in the two
beds, and their structure had not been in the least affected by the cross,
except that in a few instances the minute rudiment of the fifth stamen,

which is always present, was more fully or even completely developed. It
must not be supposed that this entire obliteration of the peloric structure in
the crossed plants can be accounted for by any incapacity of transmission;
for I raised a large bed of plants from the peloric Antirrhinum, artificially
fertilised by its own pollen, and sixteen plants, which alone survived the
winter, were all as perfectly peloric as the parent-plant. Here we have a
good instance of the wide difference between the inheritance of a character
and the power of transmitting it to crossed offspring. The crossed plants,
which perfectly resembled the common snapdragon, were allowed to sow
themselves, and, out of a hundred and twenty-seven seedlings, eighty-eight
proved to be common snapdragons, two were in an intermediate condition
between the peloric and normal state, and thirty-seven were perfectly
peloric, having reverted to the structure of their one grandparent. This case
seems at first sight to offer an exception to the rule formerly given, namely,
that a character which is present in one form and latent in the other is
generally transmitted with prepotent force when the two forms are crossed.
For in all the Scrophulariaceæ, and especially in the genera Antirrhinum
and Linaria, there is, as was shown in the last chapter, a strong latent
tendency to become peloric; and there is also, as we have just seen, a still
stronger tendency in all peloric plants to reacquire their normal irregular
structure. So that we have two opposed latent tendencies in the same plants.
Now, with the crossed Antirrhinums the tendency to produce normal or
irregular flowers, like those of the common Snapdragon, prevailed in the
first generation; whilst the tendency to pelorism, appearing to gain strength
by the intermission of a generation, prevailed to a large extent in the second
set of seedlings. How it is possible for a character to gain strength by the
intermission of a generation, will be considered in the chapter on
pangenesis.
On the whole, the subject of prepotency is extremely intricate,—from its
varying so much in strength, even in regard to the same character, in
different animals,—from its running either equally in both sexes, or, as
frequently is the case with animals, but not with plants, much stronger in
the one sex than the other,—from the existence of secondary sexual
characters,—from the transmission of certain characters being limited, as
we shall immediately see, by sex,—from certain characters not blending
together,—and, perhaps, occasionally from the effects of a previous

fertilisation on the mother. It is therefore not surprising that every one
hitherto has been baffled in drawing up general rules on the subject of
prepotency.

Inheritance as limited by Sex.
New characters often appear in one sex, and are afterwards transmitted to
the same sex, either exclusively or in a much greater degree than to the
other. This subject is important, because with animals of many kinds in a
state of nature, both high and low in the scale, secondary sexual characters,
not in any way directly connected with the organs of reproduction, are often
conspicuously present. With our domesticated animals, also, these same
secondary characters are often found to differ greatly from the state in
which they exist in the parent-species. And the principle of inheritance as
limited by sex shows how such characters might have been first acquired
and subsequently modified.

Dr. P. Lucas, who has collected many facts on this subject, shows[160]
that when a peculiarity, in no manner connected with the reproductive
organs, appears in either parent, it is often transmitted exclusively to
the offspring of the same sex, or to a much greater number of them
than of the opposite sex. Thus, in the family of Lambert, the horn-like
projections on the skin were transmitted from the father to his sons and
grandsons alone; so it has been with other cases of ichthyosis, with
supernumerary digits, with a deficiency of digits and phalanges, and in
a lesser degree with various diseases, especially with colour-blindness,
and a hæmorrhagic diathesis, that is, an extreme liability to profuse and
uncontrollable bleeding from trifling wounds. On the other hand,
mothers have transmitted, during several generations, to their
daughters alone, supernumerary and deficient digits, colour-blindness,
and other peculiarities. So that we see that the very same peculiarity
may become attached to either sex, and be long inherited by that sex
alone; but the attachment in certain cases is much more frequent to one
than the other sex. The same peculiarities also may be promiscuously
transmitted to either sex. Dr. Lucas gives other cases, showing that the
male occasionally transmits his peculiarities to his daughters alone,
and the mother to her sons alone; but even in this case we see that
inheritance is to a certain extent, though inversely, regulated by sex.

Dr. Lucas, after weighing the whole evidence, comes to the conclusion
that every peculiarity, according to the sex in which it first appears,
tends to be transmitted in a greater or lesser degree to that sex.

A few details from the many cases collected by Mr. Sedgwick,[161]
may be here given. Colour-blindness, from some unknown cause,
shows itself much oftener in males than in females; in upwards of two
hundred cases collected by Mr. Sedgwick, nine-tenths related to men;
but it is eminently liable to be transmitted through women. In the case
given by Dr. Earle, members of eight related families were affected
during five generations: these families consisted of sixty-one
individuals, namely, of thirty-two males, of whom nine-sixteenths were
incapable of distinguishing colour, and of twenty-nine females, of
whom only one-fifteenth were thus affected. Although colour-
blindness thus generally clings to the male sex, nevertheless, in one
instance in which it first appeared in a female, it was transmitted
during five generations to thirteen individuals, all of whom were
females. A hæmorrhagic diathesis, often accompanied by rheumatism,
has been known to affect the males alone during five generations,
being transmitted, however, through the females. It is said that
deficient phalanges in the fingers have been inherited by the females
alone during ten generations. In another case, a man thus deficient in
both hands and feet, transmitted the peculiarity to his two sons and one
daughter; but in the third generation, out of nineteen grandchildren,
twelve sons had the family defect, whilst the seven daughters were
free. In ordinary cases of sexual limitation, the sons or daughters
inherit the peculiarity, whatever it may be, from their father or mother,
and transmit it to their children of the same sex; but generally with the
hæmorrhagic diathesis, and often with colour-blindness, and in some
other cases, the sons never inherit the peculiarity directly from their
fathers, but the daughters, and the daughters alone, transmit the latent
tendency, so that the sons of the daughters alone exhibit it. Thus, the
father, grandson, and great-great-grandson will exhibit a peculiarity,—
the grandmother, daughter, and great-granddaughter having transmitted
it in a latent state. Hence we have, as Mr. Sedgwick remarks, a double
kind of atavism or reversion; each grandson apparently receiving and

developing the peculiarity from his grandfather, and each daughter
apparently receiving the latent tendency from her grandmother.
From the various facts recorded by Dr. Prosper Lucas, Mr. Sedgwick,
and others, there can be no doubt that peculiarities first appearing in
either sex, though not in any way necessarily or invariably connected
with that sex, strongly tend to be inherited by the offspring of the same
sex, but are often transmitted in a latent state through the opposite sex.
Turning now to domesticated animals, we find that certain characters
not proper to the parent-species are often confined to, and inherited by,
one sex alone; but we do not know the history of the first appearance
of such characters. In the chapter on Sheep, we have seen that the
males of certain races differ greatly from the females in the shape of
their horns, these being absent in the ewes of some breeds, in the
development of fat in the tail in certain fat-tailed breeds, and in the
outline of the forehead. These differences, judging from the character
of the allied wild species, cannot be accounted for by supposing that
they have been derived from distinct parent-forms. There is, also, a
great difference between the horns of the two sexes in one Indian breed
of goats. The bull zebu is said to have a larger hump than the cow. In
the Scotch deer-hound the two sexes differ in size more than in any
other variety of the dog,[162] and, judging from analogy, more than in
the aboriginal parent-species. The peculiar colour called tortoise-shell
is very rarely seen in a male cat; the males of this variety being of a
rusty tint. A tendency to baldness in man before the advent of old age
is certainly inherited; and in the European, or at least in the
Englishman, is an attribute of the male sex, and may almost be ranked
as an incipient secondary sexual character.
In various breeds of the fowl the males and females often differ
greatly; and these differences are far from being the same with those
which distinguish the two sexes in the parent-species, the Gallus
bankiva; and consequently have originated under domestication. In
certain sub-varieties of the Game race we have the unusual case of the
hens differing from each other more than the cocks. In an Indian breed
of a white colour stained with soot, the hens invariably have black
skins, and their bones are covered by a black periosteum, whilst the

cocks are never or most rarely thus characterised. Pigeons offer a more
interesting case; for the two sexes rarely differ throughout the whole
great family, and the males and females of the parent-form, the C.
livia, are undistinguishable; yet we have seen that with Pouters the
male has the characteristic quality of pouting more strongly developed
than the female; and in certain sub-varieties[163] the males alone are
spotted or striated with black. When male and female English carrier-
pigeons are exhibited in separate pens, the difference in the
development of the wattle over the beak and round the eyes is
conspicuous. So that here we have instances of the appearance of
secondary sexual characters in the domesticated races of a species in
which such differences are naturally quite absent.

On the other hand, secondary sexual characters which properly belong to
the species are sometimes quite lost, or greatly diminished, under
domestication. We see this in the small size of the tusks in our improved
breeds of the pig, in comparison with those of the wild boar. There are sub-
breeds of fowls in which the males have lost the fine flowing tail-feathers
and hackles; and others in which there is no difference in colour between
the two sexes. In some cases the barred plumage, which in gallinaceous
birds is commonly the attribute of the hen, has been transferred to the cock,
as in the cuckoo sub-breeds. In other cases masculine characters have been
partly transferred to the female, as with the splendid plumage of the golden-
spangled Hamburgh hen, the enlarged comb of the Spanish hen, the
pugnacious disposition of the Game hen, and as in the well-developed spurs
which occasionally appear in the hens of various breeds. In Polish fowls
both sexes are ornamented with a topknot, that of the male being formed of
hackle-like feathers, and this is a new male character in the genus Gallus.
On the whole, as far as I can judge, new characters are more apt to appear
in the males of our domesticated animals than in the females, and
afterwards to be either exclusively or more strongly inherited by the males.
Finally, in accordance with the principle of inheritance as limited by sex,
the appearance of secondary sexual characters in natural species offers no
especial difficulty, and their subsequent increase and modification, if of any
service to the species, would follow through that form of selection which in
my 'Origin of Species' I have called sexual selection.

Inheritance at corresponding periods of Life.
This is an important subject. Since the publication of my 'Origin of Species,'
I have seen no reason to doubt the truth of the explanation there given of
perhaps the most remarkable of all the facts in biology, namely, the
difference between the embryo and the adult animal. The explanation is,
that variations do not necessarily or generally occur at a very early period of
embryonic growth, and that such variations are inherited at a corresponding
age. As a consequence of this the embryo, even when the parent-form
undergoes a great amount of modification, is left only slightly modified;
and the embryos of widely-different animals which are descended from a
common progenitor remain in many important respects like each other and
their common progenitor. We can thus understand why embryology should

throw a flood of light on the natural system of classification, for this ought
to be as far as possible genealogical. When the embryo leads an
independent life, that is, becomes a larva, it has to be adapted to the
surrounding conditions in its structure and instincts, independently of those
of its parents; and the principle of inheritance at corresponding periods of
life renders this possible.
This principle is, indeed, in one way so obvious that it escapes attention. We
possess a number of races of animals and plants, which, when compared
with each other and with their parent-forms, present conspicuous
differences, both in the immature and mature states. Look at the seeds of the
several kinds of peas, beans, maize, which can be propagated truly, and see
how they differ in size, colour, and shape, whilst the full-grown plants differ
but little. Cabbages on the other hand differ greatly in foliage and manner of
growth, but hardly at all in their seeds; and generally it will be found that
the differences between cultivated plants at different periods of growth are
not necessarily closely connected together, for plants may differ much in
their seeds and little when full-grown, and conversely may yield seeds
hardly distinguishable, yet differ much when full-grown. In the several
breeds of poultry, descended from a single species, differences in the eggs
and chickens, in the plumage at the first and subsequent moults, in the comb
and wattles during maturity, are all inherited. With man peculiarities in the
milk and second teeth, of which I have received the details, are inheritable,
and with man longevity is often transmitted. So again with our improved
breeds of cattle and sheep, early maturity, including the early development
of the teeth, and with certain breeds of fowl the early appearance of
secondary sexual characters, all come under the same head of inheritance at
corresponding periods.
Numerous analogous facts could be given. The silk-moth, perhaps, offers
the best instance; for in the breeds which transmit their characters truly, the
eggs differ in size, colour, and shape;—the caterpillars differ, in moulting
three or four times, in colour, even in having a dark-coloured mark like an
eyebrow, and in the loss of certain instincts;—the cocoons differ in size,
shape, and in the colour and quality of the silk; these several differences
being followed by slight or barely distinguishable differences in the mature
moth.

But it may be said that, if in the above cases a new peculiarity is inherited,
it must be at the corresponding stage of development; for an egg or seed can
resemble only an egg or seed, and the horn in a full-grown ox can resemble
only a horn. The following cases show inheritance at corresponding periods
more plainly, because they refer to peculiarities which might have
supervened, as far as we can see, earlier or later in life, yet are inherited at
the same period at which they first appeared.

In the Lambert family the porcupine-like excrescences appeared in the
father and sons at the same age, namely, about nine weeks after birth.
[164] In the extraordinary hairy family described by Mr. Crawfurd,[165]

children were produced during three generations with hairy ears; in the
father the hair began to grow over his body at six years old; in his
daughter somewhat earlier, namely, at one year; and in both
generations the milk teeth appeared late in life, the permanent teeth
being afterwards singularly deficient. Greyness of hair at an unusually
early age has been transmitted in some families. These cases border on
diseases inherited at corresponding periods of life, to which I shall
immediately refer.
It is a well-known peculiarity with almond-tumbler pigeons, that the
full beauty and peculiar character of the plumage does not appear until
the bird has moulted two or three times. Neumeister describes and
figures a breed of pigeons in which the whole body is white except the
breast, neck, and head; but before the first moult all the white feathers
acquire coloured edges. Another breed is more remarkable: its first
plumage is black, with rusty-red wing-bars and a crescent-shaped mark
on the breast; these marks then became white, and remain so during
three or four moults; but after this period the white spreads over the
body, and the bird loses its beauty.[166] Prize canary-birds have their
wings and tail black: "this colour, however, is only retained until the
first moult, so that they must be exhibited ere the change takes place.
Once moulted, the peculiarity has ceased. Of course all the birds
emanating from this stock have black wings and tails the first year."
[167] A curious and somewhat analogous account has been given[168] of

a family of wild pied rooks which were first observed in 1798, near
Chalfont, and which every year from that date up to the period of the

published notice, viz. 1837, "have several of their brood particoloured,
black and white. This variegation of the plumage, however, disappears
with the first moult; but among the next young families there are
always a few pied ones." These changes of plumage, which appear and
are inherited at various corresponding periods of life in the pigeon,
canary-bird, and rook, are remarkable, because the parent-species
undergo no such change.
Inherited diseases afford evidence in some respects of less value than
the foregoing cases, because diseases are not necessarily connected
with any change in structure; but in other respects of more value,
because the periods have been more carefully observed. Certain
diseases are communicated to the child apparently by a process like
inoculation, and the child is from the first affected; such cases may be
here passed over. Large classes of diseases usually appear at certain
ages, such as St. Vitus's dance in youth, consumption in early mid-life,
gout later, and apoplexy still later; and these are naturally inherited at
the same period. But even in diseases of this class, instances have been
recorded, as with St. Vitus's dance, showing that an unusually early or
late tendency to the disease is inheritable.[169] In most cases the
appearance of any inherited disease is largely determined by certain
critical periods in each person's life, as well as by unfavourable
conditions. There are many other diseases, which are not attached to
any particular period, but which certainly tend to appear in the child at
about the same age at which the parent was first attacked. An array of
high authorities, ancient and modern, could be given in support of this
proposition. The illustrious Hunter believed in it; and Piorry[170]
cautions the physician to look closely to the child at the period when
any grave inheritable disease attacked the parent. Dr. Prosper Lucas,
[171] after collecting facts from every source, asserts that affections of

all kinds, though not related to any particular period of life, tend to
reappear in the offspring at whatever period of life they first appeared
in the progenitor.
As the subject is important, it may be well to give a few instances,
simply as illustrations, not as proof; for proof, recourse must be had to
the authorities above quoted. Some of the following cases have been

selected for the sake of showing that, when a slight departure from the
rule occurs, the child is affected somewhat earlier in life than the
parent. In the family of Le Compte blindness was inherited during
three generations, and no less than thirty-seven children and
grandchildren were all affected at about the same age, namely
seventeen or eighteen.[172] In another case a father and his four
children all became blind at twenty-one years old; in another, a
grandmother grew blind at thirty-five, her daughter at nineteen, and
three grandchildren at the ages of thirteen and eleven.[173] So with
deafness, two brothers, their father and paternal grandfather, all
became deaf at the age of forty.[174]
Esquirol gives several striking instances of insanity coming on at the
same age, as that of a grandfather, father, and son, who all committed
suicide near their fiftieth year. Many other cases could be given, as of a
whole family who became insane at the age of forty.[175] Other cerebral
affections sometimes follow the same rule,—for instance, epilepsy and
apoplexy. A woman died of the latter disease when sixty-three years
old; one of her daughters at forty-three, and the other at sixty-seven:
the latter had twelve children, who all died from tubercular meningitis.
[176]
I mention this latter case because it illustrates a frequent
occurrence, namely, a change in the precise nature of an inherited
disease, though still affecting the same organ.
Asthma has attacked several members of the same family when forty
years old, and other families during infancy. The most different
diseases, as angina pectoris, stone in the bladder, and various affections
of the skin, have appeared in successive generations at nearly the same
age. The little finger of a man began from some unknown cause to
grow inwards, and the same finger in his two sons began at the same
age to bend inwards in a similar manner. Strange and inexplicable
neuralgic affections have caused parents and children to suffer agonies
at about the same period of life.[177]
I will give only two other cases, which are interesting as illustrating the
disappearance as well as the appearance of disease at the same age.
Two brothers, their father, their paternal uncles, seven cousins, and

their paternal grandfather, were all similarly affected by a skin-disease,
called pityriasis versicolor; "the disease, strictly limited to the males of
the family (though transmitted through the females), usually appeared
at puberty, and disappeared at about the age of forty or forty-five
years." The second case is that of four brothers, who when about
twelve years old suffered almost every week from severe headaches,
which were relieved only by a recumbent position in a dark room.
Their father, paternal uncles, paternal grandfather, and paternal
granduncles all suffered in the same way from headaches, which
ceased at the age of fifty-four or fifty-five in all those who lived so
long. None of the females of the family were affected.[178]

It is impossible to read the foregoing accounts, and the many others which
have been recorded, of diseases coming on during three or even more
generations, at the same age in several members of the same family,
especially in the case of rare affections in which the coincidence cannot be
attributed to chance, and doubt that there is a strong tendency to inheritance
in disease at corresponding periods of life. When the rule fails, the disease
is apt to come on earlier in the child than in the parent; the exceptions in the
other direction being vey much rarer. Dr. Lucas[179] alludes to several cases
of inherited diseases coming on at an earlier period. I have already given
one striking instance with blindness during three generations; and Mr.
Bowman remarks that this frequently occurs with cataract. With cancer
there seems to be a peculiar liability to earlier inheritance: Mr. Paget, who
has particularly attended to this subject, and tabulated a large number of
cases, informs me that he believes that in nine cases out of ten the later
generation suffers from the disease at an earlier period than the previous
generation. He adds, "In the instances in which the opposite relation holds,
and the members of later generations have cancer at a later age than their
predecessors, I think it will be found that the non-cancerous parents have
lived to extreme old ages." So that the longevity of a non-affected parent
seems to have the power of determining in the offspring the fatal period;
and we thus apparently get another element of complexity in inheritance.
The facts, showing that with certain diseases the period of inheritance
occasionally or even frequently advances, are important with respect to the
general descent-theory, for they render it in some degree probable that the

same thing would occur with ordinary modifications of structure. The final
result of a long series of such advances would be the gradual obliteration of
characters proper to the embryo and larva, which would thus come to
resemble more and more closely the mature parent-form. But any structure
which was of service to the embryo or larva would be preserved by the
destruction at this stage of growth of each individual which manifested any
tendency to lose at too early an age its own proper character.
Finally, from the numerous races of cultivated plants and domestic animals,
in which the seed or eggs, the young or old, differ from each other and from
their parent-species;—from the cases in which new characters have
appeared at a particular period, and afterwards have been inherited at the
same period;—and from what we know with respect to disease, we must
believe in the truth of the great principle of inheritance at corresponding
periods of life.

Summary of the three preceding Chapters.—Strong as is the force of
inheritance, it allows the incessant appearance of new characters. These,
whether beneficial or injurious, of the most trifling importance, such as a
shade of colour in a flower, a coloured lock of hair, or a mere gesture; or of
the highest importance, as when affecting the brain or an organ so perfect
and complex as the eye; or of so grave a nature as to deserve to be called a
monstrosity, or so peculiar as not to occur normally in any member of the
same natural class, are all sometimes strongly inherited by man, the lower
animals, and plants. In numberless cases it suffices for the inheritance of a
peculiarity that one parent alone should be thus characterised. Inequalities
in the two sides of the body, though opposed to the law of symmetry, may
be transmitted. There is a considerable body of evidence showing that even
mutilations, and the effects of accidents, especially or perhaps exclusively
when followed by disease, are occasionally inherited. There can be no
doubt that the evil effects of long-continued exposure in the parent to
injurious conditions are sometimes transmitted to the offspring. So it is, as
we shall see in a future chapter, with the effects of the use and disuse of
parts, and of mental habits. Periodical habits are likewise transmitted, but
generally, as it would appear, with little force.

Hence we are led to look at inheritance as the rule, and non-inheritance as
the anomaly. But this power often appears to us in our ignorance to act
capriciously, transmitting a character with inexplicable strength or
feebleness. The very same peculiarity, as the weeping habit of trees, silky-
feathers, &c., may be inherited either firmly or not at all by different
members of the same group, and even by different individuals of the same
species, though treated in the same manner. In this latter case we see that
the power of transmission is a quality which is merely individual in its
attachment. As with single characters, so it is with the several concurrent
slight differences which distinguish sub-varieties or races; for of these,
some can be propagated almost as truly as species, whilst others cannot be
relied on. The same rule holds good with plants, when propagated by bulbs,
offsets, &c., which in one sense still form parts of the same individual, for
some varieties retain or inherit through successive bud-generations their
character far more truly than others.
Some characters not proper to the parent-species have certainly been
inherited from an extremely remote epoch, and may therefore be considered
as firmly fixed. But it is doubtful whether length of inheritance in itself
gives fixedness of character; though the chances are obviously in favour of
any character which has long been transmitted true or unaltered, still being
transmitted true as long as the conditions of life remain the same. We know
that many species, after having retained the same character for countless
ages, whilst living under their natural conditions, when domesticated have
varied in the most diversified manner, that is, have failed to transmit their
original form; so that no character appears to be absolutely fixed. We can
sometimes account for the failure of inheritance by the conditions of life
being opposed to the development of certain characters; and still oftener, as
with plants cultivated by grafts and buds, by the conditions causing new and
slight modifications incessantly to appear. In this latter case it is not that
inheritance wholly fails, but that new characters are continually superadded.
In some few cases, in which both parents are similarly characterised,
inheritance seems to gain so much force by the combined action of the two
parents, that it counteracts its own power, and a new modification is the
result.
In many cases the failure of the parents to transmit their likeness is due to
the breed having been at some former period crossed; and the child takes

after his grandparent or more remote ancestor of foreign blood. In other
cases, in which the breed has not been crossed, but some ancient character
has been lost through variation, it occasionally reappears through reversion,
so that the parents apparently fail to transmit their own likeness. In all
cases, however, we may safely conclude that the child inherits all its
characters from its parents, in whom certain characters are latent, like the
secondary sexual characters of one sex in the other. When, after a long
succession of bud-generations, a flower or fruit becomes separated into
distinct segments, having the colours or other attributes of both parent-
forms, we cannot doubt that these characters were latent in the earlier buds,
though they could not then be detected, or could be detected only in an
intimately commingled state. So it is with animals of crossed parentage,
which with advancing years occasionally exhibit characters derived from
one of their two parents, of which not a trace could at first be perceived.
Certain monstrosities, which resemble what naturalists call the typical form
of the group in question, apparently come under the same law of reversion.
It is assuredly an astonishing fact that the male and female sexual elements,
that buds, and even full-grown animals, should retain characters, during
several generations in the case of crossed breeds, and during thousands of
generations in the case of pure breeds, written as it were in invisible ink, yet
ready at any time to be evolved under the requisite conditions.
What these conditions are, we do not in many cases at all know. But the act
of crossing in itself, apparently from causing some disturbance in the
organisation, certainly gives a strong tendency to the reappearance of long-
lost characters, both corporeal and mental, independently of those derived
from the cross. A return of any species to its natural conditions of life, as
with feral animals and plants, favours reversion; though it is certain that this
tendency exists, we do not know how far it prevails, and it has been much
exaggerated. On the other hand, the crossed offspring of plants which have
had their organisation disturbed by cultivation, are more liable to reversion
than the crossed offspring of species which have always lived under their
natural conditions.
When distinguishable individuals of the same family, or races, or species
are crossed, we see that the one is often prepotent over the other in
transmitting its own character. A race may possess a strong power of
inheritance, and yet when crossed, as we have seen with trumpeter-pigeons,

yield to the prepotency of every other race. Prepotentcy of transmission
may be equal in the two sexes of the same species, but often runs more
strongly in one sex. It plays an important part in determining the rate at
which one race can be modified or wholly absorbed by repeated crosses
with another. We can seldom tell what makes one race or species prepotent
over another; but it sometimes depends on the same character being present
and visible in one parent, and latent or potentially present in the other.
Characters may first appear in either sex, but oftener in the male than in the
female, and afterwards be transmitted to the offspring of the same sex. In
this case we may feel confident that the peculiarity in question is really
present though latent in the opposite sex; hence the father may transmit
through his daughter any character to his grandson; and the mother
conversely to her granddaughter. We thus learn, and the fact is an important
one, that transmission and development are distinct powers. Occasionally
these two powers seem to be antagonistic, or incapable of combination in
the same individual; for several cases have been recorded in which the son
has not directly inherited a character from his father, or directly transmitted
it to his son, but has received it by transmission through his non-affected
mother, and transmitted it through his non-affected daughter. Owing to
inheritance being limited by sex, we can see how secondary sexual
characters may first have arisen under nature; their preservation and
accumulation being dependent on their service to either sex.
At whatever period of life a new character first appears, it generally remains
latent in the offspring until a corresponding age is attained, and then it is
developed. When this rule fails, the child generally exhibits the character at
an earlier period than the parent. On this principle of inheritance at
corresponding periods, we can understand how it is that most animals
display from the germ to maturity such a marvellous succession of
characters.
Finally, though much remains obscure with respect to Inheritance, we may
look at the following laws as fairly well established. Firstly, a tendency in
every character, new and old, to be transmitted by seminal and bud
generation, though often counteracted by various known and unknown
causes. Secondly, reversion or atavism, which depends on transmission and
development being distinct powers: it acts in various degrees and manners

through both seminal and bud generation. Thirdly, prepotency of
transmission, which may be confined to one sex, or be common to both
sexes of the prepotent form. Fourthly, transmission, limited by sex,
generally to the same sex in which the inherited character first appeared.
Fifthly, inheritance at corresponding periods of life, with some tendency to
the earlier development of the inherited character. In these laws of
Inheritance, as displayed under domestication, we see an ample provision
for the production, through variability and natural selection, of new specific
forms.

CHAPTER XV.

ON CROSSING.

FREE INTERCROSSING OBLITERATES THE DIFFERENCES BETWEEN ALLIED
BREEDS—WHEN THE NUMBERS OF TWO COMMINGLING BREEDS ARE
UNEQUAL, ONE ABSORBS THE OTHER—THE RATE OF ABSORPTION
DETERMINED BY PREPOTENCY OF TRANSMISSION, BY THE CONDITIONS OF
LIFE, AND BY NATURAL SELECTION—ALL ORGANIC BEINGS OCCASIONALLY
INTERCROSS; APPARENT EXCEPTIONS—ON CERTAIN CHARACTERS INCAPABLE
OF FUSION; CHIEFLY OR EXCLUSIVELY THOSE WHICH HAVE SUDDENLY
APPEARED IN THE INDIVIDUAL—ON THE MODIFICATION OF OLD RACES, AND
THE FORMATION OF NEW RACES, BY CROSSING—SOME CROSSED RACES HAVE
BRED TRUE FROM THEIR FIRST PRODUCTION—ON THE CROSSING OF DISTINCT
SPECIES IN RELATION TO THE FORMATION OF DOMESTIC RACES.

In the two previous chapters, when discussing reversion and prepotency, I
was necessarily led to give many facts on crossing. In the present chapter I
shall consider the part which crossing plays in two opposed directions,—
firstly, in obliterating characters, and consequently in preventing the
formation of new races; and secondly, in the modification of old races, or in
the formation of new and intermediate races, by a combination of
characters. I shall also show that certain characters are incapable of fusion.
The effects of free or uncontrolled breeding between the members of the
same variety or of closely allied varieties are important; but are so obvious
that they need not be discussed at much length. It is free intercrossing

which chiefly gives uniformity, both under nature and under domestication,
to the individuals of the same species or variety, when they live mingled
together and are not exposed to any cause inducing excessive variability.
The prevention of free crossing, and the intentional matching of individual
animals, are the corner-stones of the breeder's art. No man in his senses
would expect to improve or modify a breed in any particular manner, or
keep an old breed true and distinct, unless he separated his animals. The
killing of inferior animals in each generation comes to the same thing as
their separation. In savage and semi-civilised countries, where the
inhabitants have not the means of separating their animals, more than a
single breed of the same species rarely or never exists. In former times,
even in a country so civilised as North America, there were no distinct races
of sheep, for all had been mingled together.[180] The celebrated agriculturist
Marshall[181] remarks that "sheep that are kept within fences, as well as
shepherded flocks in open countries, have generally a similarity, if not a
uniformity, of character in the individuals of each flock;" for they breed
freely together, and are prevented from crossing with other kinds; whereas
in the unenclosed parts of England the unshepherded sheep, even of the
same flock, are far from true or uniform, owing to various breeds having
mingled and crossed. We have seen that the half-wild cattle in the several
British parks are uniform in character in each; but in the different parks,
from not having mingled and crossed during many generations, they differ
in a slight degree.
We cannot doubt that the extraordinary number of varieties and sub-
varieties of the pigeon, amounting to at least one hundred and fifty, is partly
due to their remaining, differently from other domesticated birds, paired for
life when once matched. On the other hand, breeds of cats imported into
this country soon disappear, for their nocturnal and rambling habits render it
hardly possible to prevent free crossing. Rengger[182] gives an interesting
case with respect to the cat in Paraguay: in all the distant parts of the
kingdom it has assumed, apparently from the effects of the climate, a
peculiar character, but near the capital this change has been prevented,
owing, as he asserts, to the native animal frequently crossing with cats
imported from Europe. In all cases like the foregoing, the effects of an
occasional cross will be augmented by the increased vigour and fertility of
the crossed offspring, of which fact evidence will hereafter be given; for

this will lead to the mongrels increasing more rapidly than the pure parent-
breeds.
When distinct breeds are allowed to cross freely, the result will be a
heterogenous body; for instance, the dogs in Paraguay are far from uniform,
and can no longer be affiliated to their parent-races.[183] The character
which a crossed body of animals will ultimately assume must depend on
several contingencies,—namely, on the relative numbers of the individuals
belonging to the two or more races which are allowed to mingle; on the
prepotency of one race over the other in the transmission of character; and
on the conditions of life to which they are exposed. When two commingled
breeds exist at first in nearly equal numbers, the whole will sooner or later
become intimately blended, but not so soon, both breeds being equally
favoured in all respects, as might have been expected. The following
calculation[184] shows that this is the case: if a colony with an equal number
of black and white men were founded, and we assume that they marry
indiscriminately, are equally prolific, and that one in thirty annually dies
and is born; then "in 65 years the number of blacks, whites, and mulattoes
would be equal. In 91 years the whites would be 1-10th, the blacks 1-10th,
and the mulattoes, or people of intermediate degrees of colour, 8-10ths of
the whole number. In three centuries not 1-100th part of the whites would
exist."
When one of two mingled races exceeds the other greatly in number, the
latter will soon be wholly, or almost wholly, absorbed and lost.[185] Thus
European pigs and dogs have been largely introduced into the islands of the
Pacific Ocean, and the native races have been absorbed and lost in the
course of about fifty or sixty years;[186] but the imported races no doubt
were favoured. Rats may be considered as semi-domesticated animals.
Some snake-rats (Mus alexandrinus) escaped in the Zoological Gardens of
London, "and for a long time afterwards the keepers frequently caught
cross-bred rats, at first half-breds, afterwards with less and less of the
character of the snake-rat, till at length all traces of it disappeared."[187] On
the other hand, in some parts of London, especially near the docks, where
fresh rats are frequently imported, an endless variety of intermediate forms
may be found between the brown, black, and snake rat, which are all three
usually ranked as distinct species.

How many generations are necessary for one species or race to absorb
another by repeated crosses has often been discussed;[188] and the requisite
number has probably been much exaggerated. Some writers have
maintained that a dozen, or score, or even more generations, are necessary;
but this in itself is improbable, for in the tenth generation there will be only
1-1024th part of foreign blood in the offspring. Gärtner found,[189] that with
plants one species could be made to absorb another in from three to five
generations, and he believes that this could always be effected in from six to
seventh generations. In one instance, however, Kölreuter[190] speaks of the
offspring of Mirabilis vulgaris, crossed during eight successive generations
by M. longiflora, as resembling this latter species so closely, that the most
scrupulous observer could detect "vix aliquam notabilem differentiam;"—
he succeeded, as he says, "ad plenariam fere transmutationem." But this
expression shows that the act of absorption was not even then absolutely
complete, though these crossed plants contained only the 1-256th part of M.
vulgaris. The conclusions of such accurate observers as Gärtner and
Kölreuter are of far higher worth than those made without scientific aim by
breeders. The most remarkable statement which I have met with of the
persistent endurance of the effects of a single cross is given by
Fleischmann,[191] who, in reference to German sheep, says "that the original
coarse sheep have 5500 fibres of wool on a square inch; grades of the third
or fourth Merino cross produced about 8000, the twentieth cross 27,000, the
perfect pure Merino blood 40,000 to 48,000." So that in this case common
German sheep crossed twenty times successively with Merinos have not by
any means acquired wool as fine as that of the pure breed. In all cases, the
rate of absorption will depend largely on the conditions of life being
favourable to any particular character; and we may suspect that there would
be under the climate of Germany a constant tendency to degeneration in the
wool of Merinos, unless prevented by careful selection; and thus perhaps
the foregoing remarkable case may be explained. The rate of absorption
must also depend on the amount of distinguishable difference between the
two forms which are crossed, and especially, as Gärtner insists, on
prepotency of transmission in the one form over the other. We have seen in
the last chapter that one of two French breeds of sheep yielded up its
character, when crossed with Merinos, very much slower than the other; and
the common German sheep referred to by Fleischmann may present an
analogous case. But in all cases there will be during many subsequent

generations more or less liability to reversion, and it is this fact which has
probably led authors to maintain that a score or more of generations are
requisite for one race to absorb another. In considering the final result of the
commingling of two or more breeds, we must not forget that the act of
crossing in itself tends to bring back long-lost characters not proper to the
immediate parent-forms.
With respect to the influence of the conditions of life on any two breeds
which are allowed to cross freely, unless both are indigenous and have long
been accustomed to the country where they live, they will, in all probability,
be unequally affected by the conditions, and this will modify the result.
Even with indigenous breeds, it will rarely or never occur that both are
equally well adapted to the surrounding circumstances; more especially
when permitted to roam freely, and not carefully tended, as will generally
be the case with breeds allowed to cross. As a consequence of this, natural
selection will to a certain extent come into action, and the best fitted will
survive, and this will aid in determining the ultimate character of the
commingled body.
How long a time it would require before such a crossed body of animals
would assume within a limited area a uniform character no one can say; that
they would ultimately become uniform from free intercrossing, and from
the survival of the fittest, we may feel assured; but the character thus
acquired would rarely or never, as we may infer from the several previous
considerations, be exactly intermediate between that of the two parent-
breeds. With respect to the very slight differences by which the individuals
of the same sub-variety, or even of allied varieties, are characterised, it is
obvious that free crossing would soon obliterate such small distinctions.
The formation of new varieties, independently of selection, would also thus
be prevented; except when the same variation continually recurred from the
action of some strongly predisposing cause. Hence we may conclude that
free crossing has in all cases played an important part in giving to all the
members of the same domestic race, and of the same natural species,
uniformity of character, though largely modified by natural selection and by
the direct action of the surrounding conditions.
On the possibility of all organic beings occasionally intercrossing.—But it
may be asked, can free crossing occur with hermaphrodite animals and

plants? All the higher animals, and the few insects which have been
domesticated, have separated sexes, and must inevitably unite for each
birth. With respect to the crossing of hermaphrodites, the subject is too large
for the present volume, and will be more properly treated in a succeeding
work. In my 'Origin of Species,' however, I have given a short abstract of
the reasons which induce me to believe that all organic beings occasionally
cross, though perhaps in some cases only at long intervals of time.[192] I
will here just recall the fact that many plants, though hermaphrodite in
structure, are unisexual in function;—such as those called by C. K.
Sprengel dichogamous, in which the pollen and stigma of the same flower
are matured at different periods; or those called by me reciprocally
dimorphic, in which the flower's own pollen is not fitted to fertilise its own
stigma; or again, the many kinds in which curious mechanical contrivances
exist, effectually preventing self-fertilisation. There are, however, many
hermaphrodite plants which are not in any way specially constructed to
favour intercrossing, but which nevertheless commingle almost as freely as
animals with separated sexes. This is the case with cabbages, radishes, and
onions, as I know from having experimented on them: even the peasants of
Liguria say that cabbages must be prevented "from falling in love" with
each other. In the orange tribe, Gallesio[193] remarks that the amelioration of
the various kinds is checked by their continual and almost regular crossing.
So it is with numerous other plants.
Nevertheless some cultivated plants can be named which rarely intercross,
as the common pea, or which never intercross, as I have reason to believe is
the case with the sweet-pea (Lathyrus odoratus); yet the structure of these
flowers certainly favours an occasional cross. The varieties of the tomato
and aubergine (Solanum) and pimenta (Pimenta vulgaris?) are said[194]
never to cross, even when growing alongside each other. But it should be
observed that these are all exotic plants, and we do not know how they
would behave in their native country when visited by the proper insects.
It must also be admitted that some few natural species appear under our
present state of knowledge to be perpetually self-fertilised, as in the case of
the Bee Ophrys (O. apifera), though adapted in its structure to be
occasionally crossed. The Leersia oryzoides produces minute enclosed
flowers which cannot possibly be crossed, and these alone, to the exclusion

of the ordinary flowers, have as yet been known to yield seed.[195] A few
additional and analogous cases could be advanced. But these facts do not
make me doubt that it is a general law of nature that the individuals of the
same species occasionally intercross, and that some great advantage is
derived from this act. It is well known (and I shall hereafter have to give
instances) that some plants, both indigenous and naturalised, rarely or never
produce flowers; or, if they flower, never produce seeds. But no one is thus
led to doubt that it is a general law of nature that phanerogamic plants
should produce flowers, and that these flowers should produce seed. When
they fail, we believe that such plants would perform their proper functions
under different conditions, or that they formerly did so and will do so again.
On analogous grounds, I believe that the few flowers which do not now
intercross, either would do so under different conditions, or that they
formerly fertilised each other at intervals—the means for effecting this
being generally still retained—and they will do so again at some future
period, unless indeed they become extinct. On this view alone, many points
in the structure and action of the reproductive organs in hermaphrodite
plants and animals are intelligible,—for instance, the male and female
organs never being so completely enclosed as to render access from without
impossible. Hence we may conclude that the most important of all the
means for giving uniformity to the individuals of the same species, namely,
the capacity of occasionally intercrossing, is present, or has been formerly
present, with all organic beings.

On certain Characters not blending.—When two breeds are crossed
their characters usually become intimately fused together; but some
characters refuse to blend, and are transmitted in an unmodified state
either from both parents or from one. When grey and white mice are
paired, the young are not piebald nor of an intermediate tint, but are
pure white or of the ordinary grey colour: so it is when white and
common collared turtle-doves are paired. In breeding Game fowls, a
great authority, Mr. J. Douglas, remarks, "I may here state a strange
fact: if you cross a black with a white game, you get birds of both
breeds of the clearest colour." Sir R. Heron crossed during many years
white, black, brown, and fawn-coloured Angora rabbits, and never
once got these colours mingled in the same animal, but often all four
colours in the same litter.[196] Additional cases could be given, but this

form of inheritance is very far from universal even with respect to the
most distinct colours. When turnspit dogs and ancon sheep, both of
which have dwarfed limbs, are crossed with common breeds, the
offspring are not intermediate in structure, but take after either parent.
When tailless or hornless animals are crossed with perfect animals, it
frequently, but by no means invariably, happens that the offspring are
either perfectly furnished with these organs or are quite destitute of
them. According to Rengger, the hairless condition of the Paraguay
dog is either perfectly or not at all transmitted to its mongrel offspring;
but I have seen one partial exception in a dog of this parentage which
had part of its skin hairy, and part naked; the parts being distinctly
separated as in a piebald animal. When Dorking fowls with five toes
are crossed with other breeds, the chickens often have five toes on one
foot and four on the other. Some crossed pigs raised by Sir R. Heron
between the solid-hoofed and common pig had not all four feet in an
intermediate condition, but two feet were furnished with properly
divided, and two with united hoofs.
Analogous facts have been observed with plants: Major Trevor Clarke
crossed the little, glabrous-leaved, annual stock (Matthiola), with
pollen of a large, red-flowered, rough-leaved, biennial stock, called
cocardeau by the French, and the result was that half the seedlings had
glabrous and the other half rough leaves, but none had leaves in an
intermediate state. That the glabrous seedlings were the product of the
rough-leaved variety, and not accidentally of the mother-plant's own
pollen, was shown by their tall and strong habit of growth.[197] In the
succeeding generations raised from the rough-leaved crossed
seedlings, some glabrous plants appeared, showing that the glabrous
character, though incapable of blending with and modifying the rough
leaves, was all the time latent in this family of plants. The numerous
plants formerly referred to, which I raised from reciprocal crosses
between the peloric and common Antirrhinum, offer a nearly parallel
case; for in the first generation all the plants resembled the common
form, and in the next generation, out of one hundred and thirty-seven
plants, two alone were in an intermediate condition, the others
perfectly resembling either the peloric or common form. Major Trevor
Clarke also fertilised the above-mentioned red-flowered stock with

pollen from the purple Queen stock, and about half the seedlings
scarcely differed in habit, and not at all in the red colour of the flower,
from the mother-plant, the other half bearing blossoms of a rich purple,
closely like those of the paternal plant. Gärtner crossed many white
and yellow-flowered species and varieties of Verbascum; and these
colours were never blended, but the offspring bore either pure white or
pure yellow blossoms; the former in the larger proportion.[198] Dr.
Herbert raised many seedlings, as he informed me, from Swedish
turnips crossed by two other varieties, and these never produced
flowers of an intermediate tint, but always like one of their parents. I
fertilised the purple sweet-pea (Lathyrus odoratus), which has a dark
reddish-purple standard-petal and violet-coloured wings and keel, with
pollen of the painted-lady sweet-pea, which has a pale cherry-coloured
standard, and almost white wings and keel; and from the same pod I
twice raised plants perfectly resembling both sorts; the greater number
resembling the father. So perfect was the resemblance, that I should
have thought there had been some mistake, if the plants which were at
first identical with the paternal variety, namely, the painted-lady, had
not later in the season produced, as mentioned in a former chapter,
flowers blotched and streaked with dark purple. I raised grandchildren
and great-grandchildren from these crossed plants, and they continued
to resemble the painted-lady, but during the later generations became
rather more blotched with purple, yet none reverted completely to the
original mother-plant, the purple sweet-pea. The following case is
slightly different, but still shows the same principle: Naudin[199] raised
numerous hybrids between the yellow Linaria vulgaris and the purple
L. purpurea, and during three successive generations the colours kept
distinct in different parts of the same flower.
From such cases as the foregoing, in which the offspring of the first
generation perfectly resemble either parent, we come by a small step to
those cases in which differently coloured flowers borne on the same
root resemble both parents, and by another step to those in which the
same flower or fruit is striped or blotched with the two parental
colours, or bears a single stripe of the colour or other characteristic
quality of one of the parent-forms. With hybrids and mongrels it
frequently or even generally happens that one part of the body

resembles more or less closely one parent and another part the other
parent; and here again some resistance to fusion, or, what comes to the
same thing, some mutual affinity between the organic atoms of the
same nature, apparently comes into play, for otherwise all parts of the
body would be equally intermediate in character. So again, when the
offspring of hybrids or mongrels, which are themselves nearly
intermediate in character, revert either wholly or by segments to their
ancestors, the principle of the affinity of similar, or the repulsion of
dissimilar atoms, must come into action. To this principle, which
seems to be extremely general, we shall recur in the chapter on
pangenesis.
It is remarkable, as has been strongly insisted upon by Isidore
Geoffroy St. Hilaire in regard to animals, that the transmission of
characters without fusion occurs most rarely when species are crossed;
I know of one exception alone, namely, with the hybrids naturally
produced between the common and hooded crow (Corvus corone and
cornix), which, however, are closely allied species, differing in nothing
except colour. Nor have I met with any well-ascertained cases of
transmission of this kind, even when one form is strongly prepotent
over another, when two races are crossed which have been slowly
formed by man's selection, and therefore resemble to a certain extent
natural species. Such cases as puppies in the same litter closely
resembling two distinct breeds, are probably due to super-fœtation,—
that is, to the influence of two fathers. All the characters above
enumerated, which are transmitted in a perfect state to some of the
offspring and not to others,—such as distinct colours, nakedness of
skin, smoothness of leaves, absence of horns or tail, additional toes,
pelorism, dwarfed structure, &c.,—have all been known to appear
suddenly in individual animals and plants. From this fact, and from the
several slight, aggregated differences which distinguish domestic races
and species from each other, not being liable to this peculiar form of
transmission, we may conclude that it is in some way connected with
the sudden appearance of the characters in question.

On the Modification of old Races and the Formation of new Races by
Crossing.—We have hitherto chiefly considered the effects of crossing in
giving uniformity of character; we must now look to an opposite result.

There can be no doubt that crossing, with the aid of rigorous selection
during several generations, has been a potent means in modifying old races,
and in forming new ones. Lord Orford crossed his famous stud of
greyhounds once with the bulldog, which breed was chosen from being
deficient in scenting powers, and from having what was wanted, courage
and perseverance. In the course of six or seven generations all traces of the
external form of the bulldog were eliminated, but courage and perseverance
remained. Certain pointers have been crossed, as I hear from the Rev. W. D.
Fox, with the foxhound, to give them dash and speed. Certain strains of
Dorking fowls have had a slight infusion of Game blood; and I have known
a great fancier who on a single occasion crossed his turbit-pigeons with
barbs, for the sake of gaining greater breadth of beak.
In the foregoing cases breeds have been crossed once, for the sake of
modifying some particular character; but with most of the improved races
of the pig, which now breed true, there have been repeated crosses,—for
instance, the improved Essex owes its excellence to repeated crosses with
the Neapolitan, together probably with some infusion of Chinese blood.[200]
So with our British sheep: almost all the races, except the Southdown, have
been largely crossed; "this, in fact, has been the history of our principal
breeds."[201] To give an example, the "Oxfordshire Downs" now rank as an
established breed.[202] They were produced about the year 1830 by crossing
"Hampshire and in some instances Southdown ewes with Cotswold rams:"
now the Hampshire ram was itself produced by repeated crosses between
the native Hampshire sheep and Southdowns; and the long-woolled
Cotswold were improved by crosses with the Leicester, which latter again is
believed to have been a cross between several long-woolled sheep. Mr.
Spooner, after considering the various cases which have been carefully
recorded, concludes "that from a judicious pairing of cross-bred animals it
is practicable to establish a new breed." On the Continent the history of
several crossed races of cattle and of other animals has been well
ascertained. To give one instance: the King of Wurtemberg, after twenty-
five years' careful breeding, that is after six or seven generations, made a
new breed of cattle from a cross between a Dutch and Swiss breed,
combined with other breeds.[203] The Sebright bantam, which breeds as true
as any other kind of fowl, was formed about sixty years ago by a
complicated cross.[204] Dark Brahmas, which are believed by some fanciers

to constitute a distinct species, were undoubtedly formed[205] in the United
States, within a recent period, by a cross between Chittagongs and Cochins.
With plants I believe there is little doubt that some kinds of turnips, now
extensively cultivated, are crossed races; and the history of a variety of
wheat which was raised from two very distinct varieties, and which after six
years' culture presented an even sample, has been recorded on good
authority.[206]
Until quite lately, cautious and experienced breeders, though not averse to a
single infusion of foreign blood, were almost universally convinced that the
attempt to establish a new race, intermediate between two widely distinct
races, was hopeless: "they clung with superstitious tenacity to the doctrine
of purity of blood, believing it to be the ark in which alone true safety could
be found."[207] Nor was this conviction unreasonable: when two distinct
races are crossed, the offspring of the first generation are generally nearly
uniform in character; but even this sometimes fails to be the case, especially
with crossed dogs and fowls, the young of which from the first are
sometimes much diversified. As cross-bred animals are generally of large
size and vigorous, they have been raised in great numbers for immediate
consumption. But for breeding they are found to be utterly useless; for
though they may be themselves uniform in character, when paired together
they yield during many generations offspring astonishingly diversified. The
breeder is driven to despair, and concludes that he will never form an
intermediate race. But from the cases already given, and from others which
have been recorded, it appears that patience alone is necessary; as Mr.
Spooner remarks, "nature opposes no barrier to successful admixture; in the
course of time, by the aid of selection and careful weeding, it is practicable
to establish a new breed." After six or seven generations the hoped-for
result will in most cases be obtained; but even then an occasional reversion,
or failure to keep true, may be expected. The attempt, however, will
assuredly fail if the conditions of life be decidedly unfavourable to the
characters of either parent-breed.[208]
Although the grandchildren and succeeding generations of cross-bred
animals are generally variable in an extreme degree, some curious
exceptions to the rule have been observed, both with crossed races and
species. Thus Boitard and Corbié[209] assert that from a Pouter and a Runt

"a Cavalier will appear, which we have classed amongst pigeons of pure
race, because it transmits all its qualities to its posterity." The editor of the
'Poultry Chronicle'[210] bred some bluish fowls from a black Spanish cock
and a Malay hen; and these remained true to colour "generation after
generation." The Himalayan breed of rabbits was certainly formed by
crossing two sub-varieties of the silver-grey rabbit; although it suddenly
assumed its present character, which differs much from that of either
parent-breed, yet it has ever since been easily and truly propagated. I
crossed some Labrador and Penguin ducks, and recrossed the mongrels with
Penguins; afterwards, most of the ducks reared during three generations
were nearly uniform in character, being brown with a white crescentic mark
on the lower part of the breast, and with some white spots at the base of the
beak; so that by the aid of a little selection a new breed might easily have
been formed. In regard to crossed varieties of plants, Mr. Beaton
remarks[211] that "Melville's extraordinary cross between the Scotch kale
and an early cabbage is as true and genuine as any on record;" but in this
case no doubt selection was practised. Gärtner[212] has given five cases of
hybrids, in which the progeny kept constant; and hybrids between Dianthus
armeria and deltoides remained true and uniform to the tenth generation.
Dr. Herbert likewise showed me a hybrid from two species of Loasa which
from its first production had kept constant during several generations.
We have seen in the earlier chapters, that some of our domesticated animals,
such as dogs, cattle, pigs, &c., are almost certainly descended from more
than one species, or wild race, if any one prefers to apply this latter term to
forms which were enabled to keep distinct in a state of nature. Hence the
crossing of aboriginally distinct species probably came into play at an early
period in the formation of our present races. From Rütimeyer's observations
there can be little doubt that this occurred with cattle; but in most cases
some one of the forms which were allowed to cross freely, will, it is
probable, have absorbed and obliterated the others. For it is not likely that
semi-civilized men would have taken the necessary pains to modify by
selection their commingled, crossed, and fluctuating stock. Nevertheless,
those animals which were best adapted to their conditions of life would
have survived through natural selection; and by this means crossing will
often have indirectly aided in the formation of primeval domesticated
breeds.

Within recent times, as far as animals are concerned, the crossing of distinct
species has done little or nothing in the formation or modification of our
races. It is not yet known whether the species of silk-moth which have been
recently crossed in France will yield permanent races. In the fourth chapter
I alluded with some hesitation to the statement that a new breed, between
the hare and rabbit, called leporides, had been formed in France, and was
found capable of propagating itself; but it is now positively affirmed[213]
that this is an error. With plants which can be multiplied by buds and
cuttings, hybridisation has done wonders, as with many kinds of Roses,
Rhododendrons, Pelargoniums, Calceolarias, and Petunias. Nearly all these
plants can be propagated by seed; most of them freely; but extremely few or
none come true by seed.
Some authors believe that crossing is the chief cause of variability,—that is,
of the appearance of absolutely new characters. Some have gone so far as to
look at it as the sole cause; but this conclusion is disproved by some of the
facts given in the chapter on Bud-variation. The belief that characters not
present in either parent or in their ancestors frequently originate from
crossing is doubtful; that they occasionally thus arise is probable; but this
subject will be more conveniently discussed in a future chapter on the
causes of Variability.
A condensed summary of this and of the three following chapters, together
with some remarks on Hybridism, will be given in the nineteenth chapter.

CHAPTER XVI.

CAUSES WHICH INTERFERE WITH THE FREE CROSSING OF
VARIETIES—INFLUENCE OF DOMESTICATION ON FERTILITY.

DIFFICULTIES IN JUDGING OF THE FERTILITY OF VARIETIES WHEN CROSSED—
VARIOUS CAUSES WHICH KEEP VARIETIES DISTINCT, AS THE PERIOD OF
BREEDING AND SEXUAL PREFERENCE—VARIETIES OF WHEAT SAID TO BE
STERILE WHEN CROSSED—VARIETIES OF MAIZE, VERBASCUM, HOLLYHOCK,
GOURDS, MELONS, AND TOBACCO, RENDERED IN SOME DEGREE MUTUALLY
STERILE—DOMESTICATION ELIMINATES THE TENDENCY TO STERILITY

NATURAL TO SPECIES WHEN CROSSED—ON THE INCREASED FERTILITY OF
UNCROSSED ANIMALS AND PLANTS FROM DOMESTICATION AND CULTIVATION.

The domesticated races of both animals and plants, when crossed, are with
extremely few exceptions quite prolific,—in some cases even more so than
the purely bred parent-races. The offspring, also, raised from such crosses
are likewise, as we shall see in the following chapter, generally more
vigorous and fertile than their parents. On the other hand, species when
crossed, and their hybrid offspring, are almost invariability in some degree
sterile; and here there seems to exist a broad and insuperable distinction
between races and species. The importance of this subject as bearing on the
origin of species is obvious; and we shall hereafter recur to it.
It is unfortunate how few precise observations have been made on the
fertility of mongrel animals and plants during several successive
generations. Dr. Broca[214] has remarked that no one has observed whether,
for instance, mongrel dogs, bred inter se, are indefinitely fertile; yet, if a
shade of infertility be detected by careful observation in the offspring of
natural forms when crossed, it is thought that their specific distinction is
proved. But so many breeds of sheep, cattle, pigs, dogs, and poultry, have
been crossed and recrossed in various ways, that any sterility, if it had
existed, would from being injurious almost certainly have been observed. In
investigating the fertility of crossed varieties many sources of doubt occur.
Whenever the least trace of sterility between two plants, however closely
allied, was observed by Kölreuter, and more especially by Gärtner, who
counted the exact number of seed in each capsule, the two forms were at
once ranked as distinct species; and if this rule be followed, assuredly it will
never be proved that varieties when crossed are in any degree sterile. We
have formerly seen that certain breeds of dogs do not readily pair together;
but no observations have been made whether, when paired, they produce the
full number of young, and whether the latter are perfectly fertile inter se;
but, supposing that some degree of sterility were found to exist, naturalists
would simply infer that these breeds were descended from aboriginally
distinct species; and it would be scarcely possible to ascertain whether or
not this explanation was the true one.
The Sebright Bantam is much less prolific than any other breed of fowls,
and is descended from a cross between two very distinct breeds, recrossed

by a third sub-variety. But it would be extremely rash to infer that the loss
of fertility was in any manner connected with its crossed origin, for it may
with more probability be attributed either to long-continued close
interbreeding, or to an innate tendency to sterility correlated with the
absence of hackles and sickle tail-feathers.
Before giving the few recorded cases of forms, which must be ranked as
varieties, being in some degree sterile when crossed, I may remark that
other causes sometimes interfere with varieties freely intercrossing. Thus
they may differ too greatly in size, as with some kinds of dogs and fowls:
for instance, the editor of the 'Journal of Horticulture, &c.,'[215] says that he
can keep Bantams with the larger breeds without much danger of their
crossing, but not with the smaller breeds, such as Games, Hamburgs, &c.
With plants a difference in the period of flowering serves to keep varieties
distinct, as with the various kinds of maize and wheat: thus Colonel Le
Couteur[216] remarks, "the Talavera wheat, from flowering much earlier
than any other kind, is sure to continue pure." In different parts of the
Falkland Islands the cattle are breaking up into herds of different colours;
and those on the higher ground, which are generally white, usually breed, as
I am informed by Admiral Sulivan, three months earlier than those on the
lowlands; and this would manifestly tend to keep the herds from blending.
Certain domestic races seem to prefer breeding with their own kind; and
this is a fact of some importance, for it is a step towards that instinctive
feeling which helps to keep closely allied species in a state of nature
distinct. We have now abundant evidence that, if it were not for this feeling,
many more hybrids would be naturally produced than is the case. We have
seen in the first chapter that the alco dog of Mexico dislikes dogs of other
breeds; and the hairless dog of Paraguay mixes less readily with the
European races, than the latter do with each other. In Germany the female
Spitz-dog is said to receive the fox more readily than will other dogs; a
female Australian Dingo in England attracted the wild male foxes. But these
differences in the sexual instinct and attractive power of the various breeds
may be wholly due to their descent from distinct species. In Paraguay the
horses have much freedom, and an excellent observer[217] believes that the
native horses of the same colour and size prefer associating with each other,
and that the horses which have been imported from Entre Rios and Banda

Oriental into Paraguay likewise prefer associating together. In Circassia six
sub-races of the horse are known and have received distinct names; and a
native proprietor of rank[218] asserts that horses of three of these races,
whilst living a free life, almost always refuse to mingle and cross, and will
even attack each other.
It has been observed, in a district stocked with heavy Lincolnshire and light
Norfolk sheep, that both kinds, though bred together, when turned out, "in a
short time separate to a sheep;" the Lincolnshires drawing off to the rich
soil, and the Norfolks to their own dry light soil; and as long as there is
plenty of grass, "the two breeds keep themselves as distinct as rooks and
pigeons." In this case different habits of life tend to keep the races distinct.
On one of the Faroe islands, not more than half a mile in diameter, the half-
wild native black sheep are said not to have readily mixed with the
imported white sheep. It is a more curious fact that the semi-monstrous
ancon sheep of modern origin "have been observed to keep together,
separating themselves from the rest of the flock, when put into enclosures
with other sheep."[219] With respect to fallow deer, which live in a semi-
domesticated condition, Mr. Bennett[220] states that the dark and pale
coloured herds, which have long been kept together in the Forest of Dean,
in High Meadow Woods, and in the New Forest, have never been known to
mingle: the dark-coloured deer, it may be added, are believed to have been
first brought by James I. from Norway, on account of their greater
hardiness. I imported from the island of Porto Santo two of the feral rabbits,
which differ, as described in the fourth chapter, from common rabbits; both
proved to be males, and, though they lived during some years in the
Zoological Gardens, the superintendent, Mr. Bartlett, in vain endeavoured
to make them breed with various tame kinds; but whether this refusal to
breed was due to any change in instinct, or simply to their extreme
wildness; or whether confinement had rendered them sterile, as often
occurs, cannot be told.
Whilst matching for the sake of experiment many of the most distinct
breeds of pigeons, it frequently appeared to me that the birds, though
faithful to their marriage vow, retained some desire after their own kind.
Accordingly I asked Mr. Wicking, who has kept a larger stock of various
breeds together than any man in England, whether he thought that they

would prefer pairing with their own kind, supposing that there were males
and females enough of each; and he without hesitation answered that he
was convinced that this was the case. It has often been noticed that the
dovecot pigeon seems to have an actual aversion towards the several fancy
breeds;[221] yet all have certainly sprung from a common progenitor. The
Rev. W. D. Fox informs me that his flocks of white and common Chinese
geese kept distinct.
These facts and statements, though some of them are incapable of proof,
resting only on the opinion of experienced observers, show that some
domestic races are led by different habits of life to keep to a certain extent
separate, and that others prefer coupling with their own kind, in the same
manner as species in a state of nature, though in a much less degree.

With respect to sterility from the crossing of domestic races, I know of
no well-ascertained case with animals. This fact, seeing the great
difference in structure between some breeds of pigeons, fowls, pigs,
dogs, &c., is extraordinary, in contrast with the sterility of many
closely allied natural species when crossed; but we shall hereafter
attempt to show that it is not so extraordinary as it at first appears. And
it may be well here to recall to mind that the amount of external
difference between two species will not safely guide us in foretelling
whether or not they will breed together,—some closely allied species
when crossed being utterly sterile, and others which are extremely
unlike being moderately fertile. I have said that no case of sterility in
crossed races rests on satisfactory evidence; but here is one which at
first seems trustworthy. Mr. Youatt,[222] and a better authority cannot
be quoted, states, that formerly in Lancashire crosses were frequently
made between longhorn and shorthorn cattle; the first cross was
excellent, but the produce was uncertain; in the third or fourth
generation the cows were bad milkers; "in addition to which, there was
much uncertainty whether the cows would conceive; and full one-third
of the cows among some of these half-breds failed to be in calf." This
at first seems a good case; but Mr. Wilkinson states,[223] that a breed
derived from this same cross was actually established in another part of
England; and if it had failed in fertility, the fact would surely have
been noticed. Moreover, supposing that Mr. Youatt had proved his

case, it might be argued that the sterility was wholly due to the two
parent-breeds being descended from primordially distinct species.
I will give a case with plants, to show how difficult it is to get
sufficient evidence. Mr. Sheriff, who has been so successful in the
formation of new races of wheat, fertilised the Hopetoun with the
Talavera; in the first and second generations the produce was
intermediate in character, but in the fourth generation "it was found to
consist of many varieties; nine-tenths of the florets proved barren, and
many of the seeds seemed shrivelled abortions, void of vitality, and the
whole race was evidently verging to extinction."[224] Now, considering
how little these varieties of wheat differ in any important character, it
seems to me very improbable that the sterility resulted, as Mr. Sheriff
thought, from the cross, but from some quite distinct cause. Until such
experiments are many times repeated, it would be rash to trust them;
but unfortunately they have been rarely tried even once with sufficient
care.
Gärtner has recorded a more remarkable and trustworthy case: he
fertilised thirteen panicles (and subsequently nine others) on a dwarf
maize bearing yellow seed[225] with pollen of a tall maize having red
seed; and one head alone produced good seed, only five in number.
Though these plants are monœcious, and therefore do not require
castration, yet I should have suspected some accident in the
manipulation had not Gärtner expressly stated that he had during many
years grown these two varieties together, and they did not
spontaneously cross; and this, considering that the plants are
monœcious and abound with pollen, and are well known generally to
cross freely, seems explicable only on the belief that these two
varieties are in some degree mutually infertile. The hybrid plants raised
from the above five seed were intermediate in structure, extremely
variable, and perfectly fertile.[226] No one, I believe, has hitherto
suspected that these varieties of maize are distinct species; but had the
hybrids been in the least sterile, no doubt Gärtner would at once have
so classed them. I may here remark, that with undoubted species there
is not necessarily any close relation between the sterility of a first cross
and that of the hybrid offspring. Some species can be crossed with

facility, but produce utterly sterile hybrids; others can be crossed with
extreme difficulty, but the hybrids when produced are moderately
fertile. I am not aware, however, of any instance quite like this of the
maize with natural species, namely, of a first cross made with
difficulty, but yielding perfectly fertile hybrids.
The following case is much more remarkable, and evidently perplexed
Gärtner, whose strong wish it was to draw a broad line of distinction
between species and varieties. In the genus Verbascum, he made,
during eighteen years, a vast number of experiments, and crossed no
less than 1085 flowers and counted their seeds. Many of these
experiments consisted in crossing white and yellow varieties of both V.
lychnitis and V. blattaria with nine other species and their hybrids.
That the white and yellow flowered plants of these two species are
really varieties, no one has doubted; and Gärtner actually raised in the
case of both species one variety from the seed of the other. Now in two
of his works[227] he distinctly asserts that crosses between similarly-
coloured flowers yield more seed than between dissimilarly-coloured;
so that the yellow-flowered variety of either species (and conversely
with the white-flowered variety), when crossed with pollen of its own
kind, yields more seed than when crossed with that of the white
variety; and so it is when differently coloured species are crossed. The
general results may be seen in the Table at the end of his volume. In
one instance he gives[228] the following details; but I must premise that
Gärtner, to avoid exaggerating the degree of sterility in his crosses,
always compares the maximum number obtained from a cross with the
average number naturally given by the pure mother-plant. The white-
variety of V. lychnitis, naturally fertilised by its own pollen, gave from
an average of twelve capsules ninety-six good seeds in each; whilst
twenty flowers fertilised with pollen from the yellow variety of this
same species, gave as the maximum only eighty-nine good seed; so that
we have the proportion of 1000 to 908, according to Gärtner's usual
scale. I should have thought it possible that so small a difference in
fertility might have been accounted for by the evil effects of the
necessary castration; but Gärtner shows that the white variety of V.
lychnitis, when fertilised first by the white variety of V. blattaria, and
then by the yellow variety of this species, yielded seed in the

proportion of 622 to 438; and in both these cases castration was
performed. Now the sterility which results from the crossing of the
differently coloured varieties of the same species, is fully as great as
that which occurs in many cases when distinct species are crossed.
Unfortunately Gärtner compared the results of the first unions alone,
and not the sterility of the two sets of hybrids produced from the white
variety of V. lychnitis when fertilised by the white and yellow varieties
of V. blattaria, for it is probable that they would have differed in this
respect.
Mr. J. Scott has given me the results of a series of experiments on
Verbascum, made by him in the Botanic Gardens of Edinburgh. He
repeated some of Gärtner's experiments on distinct species, but
obtained only fluctuating results; some confirmatory, but the greater
number contradictory; nevertheless these seem hardly sufficient to
overthrow the conclusions arrived at by Gärtner from experiments tried
on a much larger scale. In the second place Mr. Scott experimented on
the relative fertility of unions between similarly and dissimilarly-
coloured varieties of the same species. Thus he fertilised six flowers of
the yellow variety of V. lychnitis by its own pollen, and obtained six
capsules, and calling, for the sake of having a standard of comparison,
the average number of good seed in each one hundred, he found that
this same yellow variety, when fertilised by the white variety, yielded
from seven capsules an average of ninety-four seed. On the same
principle, the white variety of V. lychnitis by its own pollen (from six
capsules), and by the pollen of the yellow variety (eight capsules),
yielded seed in the proportion of 100 to 82. The yellow variety of V.
thapsus by its own pollen (eight capsules), and by that of the white
variety (only two capsules), yielded seed in the proportion of 100 to
94. Lastly, the white variety of V. blattaria by its own pollen (eight
capsules), and by that of the yellow variety (five capsules), yielded
seed in the proportion of 100 to 79. So that in every case the unions of
dissimilarly-coloured varieties of the same species were less fertile
than the unions of similarly-coloured varieties; when all the cases are
grouped together, the difference of fertility is as 86 to 100. Some
additional trials were made, and altogether thirty-six similarly-
coloured unions yielded thirty-five good capsules; whilst thirty-five

dissimilarly-coloured unions yielded only twenty-six good capsules.
Besides the foregoing experiments, the purple V. phœniceum was
crossed by a rose-coloured and a white variety of the same species;
these two varieties were also crossed together, and these several unions
yielded less seed than V. phœniceum by its own pollen. Hence it
follows from Mr. Scott's experiments, that in the genus Verbascum the
similarly and dissimilarly-coloured varieties of the same species
behave, when crossed, like closely allied but distinct species.[229]
This remarkable fact of the sexual affinity of similarly-coloured
varieties, as observed by Gärtner and Mr. Scott, may not be of very
rare occurrence; for the subject has not been attended to by others. The
following case is worth giving, partly to show how difficult it is to
avoid error. Dr. Herbert[230] has remarked that variously-coloured
double varieties of the hollyhock (Althæa rosea) may be raised with
certainty by seed from plants growing close together. I have been
informed that nurserymen who raise seed for sale do not separate their
plants; accordingly I procured seed of eighteen named varieties; of
these, eleven varieties produced sixty-two plants all perfectly true to
their kind; and seven produced forty-nine plants, half of which were
true and half false. Mr. Masters of Canterbury has given me a more
striking case; he saved seed from a great bed of twenty-four named
varieties planted in closely adjoining rows, and each variety
reproduced itself truly with only sometimes a shade of difference in
tint. Now in the hollyhock the pollen, which is abundant, is matured
and nearly all shed before the stigma of the same flower is ready to
receive it;[231] and as bees covered with pollen incessantly fly from
plant to plant, it would appear that adjoining varieties could not escape
being crossed. As, however, this does not occur, it appeared to me
probable that the pollen of each variety was prepotent on its own
stigma over that of all other varieties. But Mr. C. Turner of Slough,
well known for his success in the cultivation of this plant, informs me
that it is the doubleness of the flowers which prevents the bees gaining
access to the pollen and stigma; and he finds that it is difficult even to
cross them artificially. Whether this explanation will fully account for
varieties in close proximity propagating themselves so truly by seed, I
do not know.

The following cases are worth giving, as they relate to monœcious
forms, which do not require, and consequently have not been injured
by, castration. Girou de Buzareingues crossed what he designates three
varieties of gourd,[232] and asserts that their mutual fertilisation is less
easy in proportion to the difference which they present. I am aware
how imperfectly the forms in this group were until recently known; but
Sageret,[233] who ranked them according to their mutual fertility,
considers the three forms above alluded to as varieties, as does a far
higher authority, namely, M. Naudin.[234] Sageret[235] has observed that
certain melons have a greater tendency, whatever the cause may be, to
keep true than others; and M. Naudin, who has had such immense
experience in this group, informs me that he believes that certain
varieties intercross more readily than others of the same species; but he
has not proved the truth of this conclusion; the frequent abortion of the
pollen near Paris being one great difficulty. Nevertheless, he has grown
close together, during seven years, certain forms of Citrullus, which, as
they could be artificially crossed with perfect facility and produced
fertile offspring, are ranked as varieties; but these forms when not
artificially crossed kept true. Many other varieties, on the other hand,
in the same group cross with such facility, as M. Naudin repeatedly
insists, that without being grown far apart they cannot be kept in the
least true.
Another case, though somewhat different, may be here given, as it is
highly remarkable, and is established on excellent evidence. Kölreuter
minutely describes five varieties of the common tobacco,[236] which
were reciprocally crossed, and the offspring were intermediate in
character and as fertile as their parents: from this fact Kölreuter
inferred that they are really varieties; and no one, as far as I can
discover, seems to have doubted that such is the case. He also crossed
reciprocally these five varieties with N. glutinosa, and they yielded
very sterile hybrids; but those raised from the var. perennis, whether
used as the father or mother plant, were not so sterile as the hybrids
from the four other varieties.[237] So that the sexual capacity of this one
variety has certainly been in some degree modified, so as to approach
in nature that of N. glutinosa.[238]

These facts with respect to plants show that in some few cases certain
varieties have had their sexual powers so far modified, that they cross
together less readily and yield less seed than other varieties of the same
species. We shall presently see that the sexual functions of most animals
and plants are eminently liable to be affected by the conditions of life to
which they are exposed; and hereafter we shall briefly discuss the conjoint
bearing of this and other facts on the difference in fertility between crossed
varieties and crossed species.

Domestication eliminates the tendency to Sterility which is general with
Species when crossed.

This hypothesis was first propounded by Pallas,[239] and has been adopted
by several authors. I can find hardly any direct facts in its support; but
unfortunately no one has compared, in the case of either animals or plants,
the fertility of anciently domesticated varieties, when crossed with a distinct
species, with that of the wild parent-species when similarly crossed. No one
has compared, for instance, the fertility of Gallus bankiva and of the
domesticated fowl, when crossed with a distinct species of Gallus or
Phasianus; and the experiment would in all cases be surrounded by many
difficulties. Dureau de la Malle, who has so closely studied classical
literature, states[240] that in the time of the Romans the common mule was
produced with more difficulty than at the present day; but whether this
statement may be trusted I know not. A much more important, though
somewhat different, case is given by M. Groenland,[241] namely, that plants,
known from their intermediate character and sterility to be hybrids between
Ægilops and wheat, have perpetuated themselves under culture since 1857,
with a rapid but varying increase of fertility in each generation. In the
fourth generation the plants, still retaining their intermediate character, had
become as fertile as common cultivated wheat.
The indirect evidence in favour of the Pallasian doctrine appears to me to be
extremely strong. In the earlier chapters I have attempted to show that our
various breeds of dogs are descended from several wild species; and this
probably is the case with sheep. There can no longer be any doubt that the
Zebu or humped Indian ox belongs to a distinct species from European
cattle: the latter, moreover, are descended from two or three forms, which
may be called either species or wild races, but which co-existed in a state of

nature and kept distinct. We have good evidence that our domesticated pigs
belong to at least two specific types, S. scrofa and Indica, which probably
lived together in a wild state in South-eastern Europe. Now, a widely-
extended analogy leads to the belief that if these several allied species, in
the wild state or when first reclaimed, had been crossed, they would have
exhibited, both in their first unions and in their hybrid offspring, some
degree of sterility. Nevertheless the several domesticated races descended
from them are now all, as far as can be ascertained, perfectly fertile
together. If this reasoning be trustworthy, and it is apparently sound, we
must admit the Pallasian doctrine that long-continued domestication tends
to eliminate that sterility which is natural to species when crossed in their
aboriginal state.

On increased Fertility from Domestication and Cultivation.
Increased fertility from domestication, without any reference to crossing,
may be here briefly considered. This subject bears indirectly on two or three
points connected with the modification of organic beings. As Buffon long
ago remarked,[242] domestic animals breed oftener in the year and produce
more young at a birth than wild animals of the same species; they, also,
sometimes breed at an earlier age. The case would hardly have deserved
further notice, had not some authors lately attempted to show that fertility
increases and decreases in an inverse ratio with the amount of food. This
strange doctrine has apparently arisen from individual animals when
supplied with an inordinate quantity of food, and from plants of many kinds
when grown on excessively rich soil, as on a dunghill, becoming sterile; but
to this latter point I shall have occasion presently to return. With hardly an
exception, our domesticated animals, which have long been habituated to a
regular and copious supply of food, without the labour of searching for it,
are more fertile than the corresponding wild animals. It is notorious how
frequently cats and dogs breed, and how many young they produce at a
birth. The wild rabbit is said generally to breed four times yearly, and to
produce from four to eight young; the tame rabbit breeds six or seven times
yearly, and produces from four to eleven young. The ferret, though
generally so closely confined, is more prolific than its supposed wild
prototype. The wild sow is remarkably prolific, for she often breeds twice in
the year, and produces from four to eight and sometimes even twelve young

at a birth; but the domestic sow regularly breeds twice a year, and would
breed oftener if permitted; and a sow that produces less than eight at a birth
"is worth little, and the sooner she is fattened for the butcher the better."
The amount of food affects the fertility even of the same individual: thus
sheep, which on mountains never produce more than one lamb at a birth,
when brought down to lowland pastures frequently bear twins. This
difference apparently is not due to the cold of the higher land, for sheep and
other domestic animals are said to be extremely prolific in Lapland. Hard
living, also, retards the period at which animals conceive; for it has been
found disadvantageous in the northern islands of Scotland to allow cows to
bear calves before they are four years old.[243]

Birds offer still better evidence of increased fertility from
domestication: the hen of the wild Gallus bankiva lays from six to ten
eggs, a number which would be thought nothing of with the domestic
hen. The wild duck lays from five to ten eggs; the tame one in the
course of the year from eighty to one hundred. The wild grey-lag goose
lays from five to eight eggs; the tame from thirteen to eighteen, and
she lays a second time; as Mr. Dixon has remarked, "high-feeding,
care, and moderate warmth induce a habit of prolificacy which
becomes in some measure hereditary." Whether the semi-domesticated
dovecot pigeon is more fertile than the wild rock-pigeon C. livia, I
know not; but the more thoroughly domesticated breeds are nearly
twice as fertile as dovecots: the latter, however, when caged and highly
fed, become equally fertile with house pigeons. The peahen alone of
domesticated birds is rather more fertile, according to some accounts,
when wild in its native Indian home, than when domesticated in
Europe and exposed to our much colder climate.[244]
With respect to plants, no one would expect wheat to tiller more, and
each ear to produce more grain, in poor than in rich soil; or to get in
poor soil a heavy crop of peas or beans. Seeds vary so much in number
that it is difficult to estimate them; but on comparing beds of carrots
saved for seed in a nursery garden with wild plants, the former seemed
to produce about twice as much seed. Cultivated cabbages yielded
thrice as many pods by measure as wild cabbages from the rocks of
South Wales. The excess of berries produced by the cultivated

Asparagus in comparison with the wild plant is enormous. No doubt
many highly cultivated plants, such as pears, pineapples, bananas,
sugar-cane, &c., are nearly or quite sterile; and I am inclined to
attribute this sterility to excess of food and to other unnatural
conditions; but to this subject I shall presently recur.

In some cases, as with the pig, rabbit, &c., and with those plants which are
valued for their seed, the direct selection of the more fertile individuals has
probably much increased their fertility; and in all cases this may have
occurred indirectly, from the better chance of the more numerous offspring
produced by the more fertile individuals having survived. But with cats,
ferrets, and dogs, and with plants like carrots, cabbages, and asparagus,
which are not valued for their prolificacy, selection can have played only a
subordinate part; and their increased fertility must be attributed to the more
favourable conditions of life under which they have long existed.

CHAPTER XVII.

ON THE GOOD EFFECTS OF CROSSING, AND ON THE EVIL
EFFECTS OF CLOSE INTERBREEDING.

DEFINITION OF CLOSE INTERBREEDING—AUGMENTATION OF MORBID
TENDENCIES—GENERAL EVIDENCE ON THE GOOD EFFECTS DERIVED FROM
CROSSING, AND ON THE EVIL EFFECTS FROM CLOSE INTERBREEDING—
CATTLE, CLOSELY INTERBRED; HALF-WILD CATTLE LONG KEPT IN THE SAME
PARKS—SHEEP—FALLOW-DEER—DOGS—RABBITS—PIGS—MAN, ORIGIN
OF HIS ABHORRENCE OF INCESTUOUS MARRIAGES—FOWLS—PIGEONS—
HIVE-BEES—PLANTS, GENERAL CONSIDERATIONS ON THE BENEFITS DERIVED
FROM CROSSING—MELONS, FRUIT-TREES, PEAS, CABBAGES, WHEAT, AND
FOREST-TREES—ON THE INCREASED SIZE OF HYBRID PLANTS, NOT
EXCLUSIVELY DUE TO THEIR STERILITY—ON CERTAIN PLANTS WHICH EITHER
NORMALLY OR ABNORMALLY ARE SELF-IMPOTENT, BUT ARE FERTILE, BOTH
ON THE MALE AND FEMALE SIDE, WHEN CROSSED WITH DISTINCT
INDIVIDUALS EITHER OF THE SAME OR ANOTHER SPECIES—CONCLUSION.

The gain in constitutional vigour, derived from an occasional cross between
individuals of the same variety, but belonging to distinct families, or

between distinct varieties, has not been so largely or so frequently
discussed, as have the evil effects of too close interbreeding. But the former
point is the more important of the two, inasmuch as the evidence is more
decisive. The evil results from close interbreeding are difficult to detect, for
they accumulate slowly, and differ much in degree with different species;
whilst the good effects which almost invariably follow a cross are from the
first manifest. It should, however, be clearly understood that the advantage
of close interbreeding, as far as the retention of character is concerned, is
indisputable, and often outweighs the evil of a slight loss of constitutional
vigour. In relation to the subject of domestication, the whole question is of
some importance, as too close interbreeding interferes with the
improvement of old races, and especially with the formation of new ones. It
is important as indirectly bearing on Hybridism; and perhaps on the
extinction of species, when any form has become so rare that only a few
individuals remain within a confined area. It bears in an important manner
on the influence of free intercrossing, in obliterating individual differences,
and thus giving uniformity of character to the individuals of the same race
or species; for if additional vigour and fertility be thus gained, the crossed
offspring will multiply and prevail, and the ultimate result will be far
greater than otherwise would have occurred. Lastly, the question is of high
interest, as bearing on mankind. Hence I shall discuss this subject at full
length. As the facts which prove the evil effects of close interbreeding are
more copious, though less decisive, than those on the good effects of
crossing, I shall, under each group of beings, begin with the former.
There is no difficulty in defining what is meant by a cross; but this is by no
means easy in regard to "breeding in and in" or "too close interbreeding,"
because, as we shall see, different species of animals are differently affected
by the same degree of interbreeding. The pairing of a father and daughter,
or mother and son, or brothers and sisters, if carried on during several
generations, is the closest possible form of interbreeding. But some good
judges, for instance Sir J. Sebright, believe that the pairing of a brother and
sister is closer than that of parents and children; for when the father is
matched with his daughter he crosses, as is said, with only half his own
blood. The consequences of close interbreeding carried on for too long a
time, are, as is generally believed, loss of size, constitutional vigour, and
fertility, sometimes accompanied by a tendency to malformation. Manifest

evil does not usually follow from pairing the nearest relations for two,
three, or even four generations; but several causes interfere with our
detecting the evil—such as the deterioration being very gradual, and the
difficulty of distinguishing between such direct evil and the inevitable
augmentation of any morbid tendencies which may be latent or apparent in
the related parents. On the other hand, the benefit from a cross, even when
there has not been any very close interbreeding, is almost invariably at once
conspicuous. There is reason to believe, and this was the opinion of that
most experienced observer Sir J. Sebright,[245] that the evil effects of close
interbreeding may be checked by the related individuals being separated
during a few generations and exposed to different conditions of life.
That evil directly follows from any degree of close interbreeding has been
denied by many persons; but rarely by any practical breeder; and never, as
far as I know, by one who has largely bred animals which propagate their
kind quickly. Many physiologists attribute the evil exclusively to the
combination and consequent increase of morbid tendencies common to both
parents: that this is an active source of mischief there can be no doubt. It is
unfortunately too notorious that men and various domestic animals
endowed with a wretched constitution, and with a strong hereditary
disposition to disease, if not actually ill, are fully capable of procreating
their kind. Close interbreeding, on the other hand, induces sterility; and this
indicates something quite distinct from the augmentation of morbid
tendencies common to both parents. The evidence immediately to be given
convinces me that it is a great law of nature, that all organic beings profit
from an occasional cross with individuals not closely related to them in
blood; and that, on the other hand, long-continued close interbreeding is
injurious.
Various general considerations have had much influence in leading me to
this conclusion; but the reader will probably rely more on special facts and
opinions. The authority of experienced observers, even when they do not
advance the grounds of their belief, is of some little value. Now almost all
men who have bred many kinds of animals and have written on the subject,
such as Sir J. Sebright, Andrew Knight, &c.,[246] have expressed the
strongest conviction on the impossibility of long-continued close
interbreeding. Those who have compiled works on agriculture, and have
associated much with breeders, such as the sagacious Youatt, Low, &c.,

have strongly declared their opinion to the same effect. Prosper Lucas,
trusting largely to French authorities, has come to a similar conclusion. The
distinguished German agriculturist Hermann von Nathusius, who has
written the most able treatise on this subject which I have met with,
concurs; and as I shall have to quote from this treatise, I may state that
Nathusius is not only intimately acquainted with works on agriculture in all
languages, and knows the pedigrees of our British breeds better than most
Englishmen, but has imported many of our improved animals, and is
himself an experienced breeder.
Evidence of the evil effects of close interbreeding can most readily be
acquired in the case of animals, such as fowls, pigeons, &c., which
propagate quickly, and, from being kept in the same place, are exposed to
the same conditions. Now I have inquired of very many breeders of these
birds, and I have hitherto not met with a single man who was not
thoroughly convinced that an occasional cross with another strain of the
same sub-variety was absolutely necessary. Most breeders of highly-
improved or fancy birds value their own strain, and are most unwilling, at
the risk, in their opinion, of deterioration, to make a cross. The purchase of
a first-rate bird of another strain is expensive, and exchanges are
troublesome; yet all breeders, as far as I can hear, excepting those who keep
large stocks at different places for the sake of crossing, are driven after a
time to take this step.
Another general consideration which has had great influence on my mind
is, that with all hermaphrodite animals and plants, which it might have been
thought would have perpetually fertilised themselves, and thus have been
subjected for long ages to the closest interbreeding, there is no single
species, as far as I can discover, in which the structure ensures self-
fertilisation. On the contrary, there are in a multitude of cases, as briefly
stated in the fifteenth chapter, manifest adaptations which favour or
inevitably lead to an occasional cross between one hermaphrodite and
another of the same species; and these adaptive structures are utterly
purposeless, as far as we can see, for any other end.

With Cattle there can be no doubt that extremely close interbreeding
may be long carried on, advantageously with respect to external
characters and with no manifestly apparent evil as far as constitution is

concerned. The same remark is applicable to sheep. Whether these
animals have gradually been rendered less susceptible than others to
this evil, in order to permit them to live in herds,—a habit which leads
the old and vigorous males to expel all intruders, and in consequence
often to pair with their own daughters, I will not pretend to decide. The
case of Bakewell's Long-horns, which were closely interbred for a long
period, has often been quoted; yet Youatt says[247] the breed "had
acquired a delicacy of constitution inconsistent with common
management," and "the propagation of the species was not always
certain." But the Shorthorns offer the most striking case of close
interbreeding; for instance, the famous bull Favourite (who was
himself the offspring of a half-brother and sister from Foljambe) was
matched with his own daughter, granddaughter, and great-
granddaughter; so that the produce of this last union, or the great-great-
granddaughter, had 15-16ths, or 93.75 per cent. of the blood of
Favourite in her veins. This cow was matched with the bull Wellington,
having 62.5 per cent. of Favourite blood in his veins, and produced
Clarissa; Clarissa was matched with the bull Lancaster, having 68.75
of the same blood, and she yielded valuable offspring.[248]
Nevertheless Collings, who reared these animals, and was a strong
advocate for close breeding, once crossed his stock with a Galloway,
and the cows from this cross realised the highest prices. Bates's herd
was esteemed the most celebrated in the world. For thirteen years he
bred most closely in and in; but during the next seventeen years,
though he had the most exalted notion of the value of his own stock, he
thrice infused fresh blood into his herd: it is said that he did this, not to
improve the form of his animals, but on account of their lessened
fertility. Mr. Bates's own view, as given by a celebrated breeder,[249]
was, that "to breed in and in from a bad stock was ruin and
devastation; yet that the practice may be safely followed within certain
limits when the parents so related are descended from first-rate
animals." We thus see that there has been extremely close
interbreeding with Shorthorns; but Nathusius, after the most careful
study of their pedigrees, says that he can find no instance of a breeder
who has strictly followed this practice during his whole life. From this
study and his own experience, he concludes that close interbreeding is
necessary to ennoble the stock; but that in effecting this the greatest

care is necessary, on account of the tendency to infertility and
weakness. It may be added, that another high authority[250] asserts that
many more calves are born cripples from Shorthorns than from other
and less closely interbred races of cattle.
Although by carefully selecting the best animals (as Nature effectually
does by the law of battle) close interbreeding may be long carried on
with cattle, yet the good effects of a cross between almost any two
breeds is at once shown by the greater size and vigour of the offspring;
as Mr. Spooner writes to me, "crossing distinct breeds certainly
improves cattle for the butcher." Such crossed animals are of course of
no value to the breeder; but they have been raised during many years in
several parts of England to be slaughtered;[251] and their merit is now
so fully recognised, that at fat-cattle shows a separate class has been
formed for their reception. The best fat ox at the great show at
Islington in 1862 was a crossed animal.
The half-wild cattle, which have been kept in British parks probably
for 400 or 500 years, or even for a longer period, have been advanced
by Culley and others as a case of long-continued interbreeding within
the limits of the same herd without any consequent injury. With respect
to the cattle at Chillingham, the late Lord Tankerville owned that they
were bad breeders.[252] The agent, Mr. Hardy, estimates (in a letter to
me, dated May, 1861) that in the herd of about fifty the average
number annually slaughtered, killed by fighting, and dying, is about
ten, or one in five. As the herd is kept up to nearly the same average
number, the annual rate of increase must be likewise about one in five.
The bulls, I may add, engage in furious battles, of which battles the
present Lord Tankerville has given me a graphic description, so that
there will always be rigorous selection of the most vigorous males. I
procured in 1855 from Mr. D. Gardner, agent to the Duke of Hamilton,
the following account of the wild cattle kept in the Duke's park in
Lanarkshire, which is about 200 acres in extent. The number of cattle
varies from sixty-five to eighty; and the number annually killed (I
presume by all causes) is from eight to ten; so that the annual rate of
increase can hardly be more than one in six. Now in South America,
where the herds are half-wild, and therefore offer a nearly fair standard

of comparison, according to Azara the natural increase of the cattle on
an estancia is from one-third to one-fourth of the total number, or one
in between three and four; and this, no doubt, applies exclusively to
adult animals fit for consumption. Hence the half-wild British cattle
which have long interbred within the limits of the same herd are
relatively far less fertile. Although in an unenclosed country like
Paraguay there must be some crossing between the different herds, yet
even there the inhabitants believe that the occasional introduction of
animals from distant localities is necessary to prevent "degeneration in
size and diminution of fertility."[253] The decrease in size from ancient
times in the Chillingham and Hamilton cattle must have been
prodigious, for Professor Rütimeyer has shown that they are almost
certainly the descendants of the gigantic Bos primigenius. No doubt
this decrease in size may be largely attributed to less favourable
conditions of life; yet animals roaming over large parks, and fed during
severe winters, can hardly be considered as placed under very
unfavourable conditions.
With Sheep there has often been long-continued interbreeding within
the limits of the same flock; but whether the nearest relations have
been matched so frequently as in the case of Shorthorn cattle, I do not
know. The Messrs. Brown during fifty years have never infused fresh
blood into their excellent flock of Leicesters. Since 1810 Mr. Barford
has acted on the same principle with the Foscote flock. He asserts that
half a century of experience has convinced him that when two nearly
related animals are quite sound in constitution, in-and-in breeding does
not induce degeneracy; but he adds that he "does not pride himself on
breeding from the nearest affinities." In France the Naz flock has been
bred for sixty years without the introduction of a single strange ram.
[254]
Nevertheless, most great breeders of sheep have protested against
close interbreeding prolonged for too great a length of time.[255] The
most celebrated of recent breeders, Jonas Webb, kept five separate
families to work on, thus "retaining the requisite distance of
relationship between the sexes."[256]
Although by the aid of careful selection the near interbreeding of sheep
may be long continued without any manifest evil, yet it has often been

the practice with farmers to cross distinct breeds to obtain animals for
the butcher, which plainly shows that good is derived from this
practice. Mr. Spooner sums up his excellent Essay on Crossing by
asserting that there is a direct pecuniary advantage in judicious cross-
breeding, especially when the male is larger than the female. A former
celebrated breeder, Lord Somerville, distinctly states that his half-
breeds from Ryelands and Spanish sheep were larger animals than
either the pure Ryelands or pure Spanish sheep.[257]
As some of our British parks are ancient, it occurred to me that there
must have been long-continued close interbreeding with the fallow
deer (Cervus dama) kept in them; but on inquiry I find that it is a
common practice to infuse new blood by procuring bucks from other
parks. Mr. Shirley,[258] who has carefully studied the management of
deer, admits that in some parks there has been no admixture of foreign
blood from a time beyond the memory of man. But he concludes "that
in the end the constant breeding in-and-in is sure to tell to the
disadvantage of the whole herd, though it may take a very long time to
prove it; moreover, when we find, as is very constantly the case, that
the introduction of fresh blood has been of the very greatest use to
deer, both by improving their size and appearance, and particularly by
being of service in removing the taint of 'rickback,' if not of other
diseases, to which deer are sometimes subject when the blood has not
been changed, there can, I think, be no doubt but that a judicious cross
with a good stock is of the greatest consequence, and is indeed
essential, sooner or later, to the prosperity of every well-ordered park."
Mr. Meynell's famous foxhounds have been adduced, as showing that
no ill effects follow from close interbreeding; and Sir J. Sebright
ascertained from him that he frequently bred from father and daughter,
mother and son, and sometimes even from brothers and sisters. Sir J.
Sebright, however, declares,[259] that by breeding in-and-in, by which
he means matching brothers and sisters, he has actually seen strong
spaniels become weak and diminutive lapdogs. The Rev. W. D. Fox
has communicated to me the case of a small lot of bloodhounds, long
kept in the same family, which had become very bad breeders, and
nearly all had a bony enlargement in the tail. A single cross with a

distinct strain of bloodhounds restored their fertility, and drove away
the tendency to malformation in the tail. I have heard the particulars of
another case with bloodhounds, in which the female had to be held to
the male. Considering how rapid is the natural increase of the dog, it is
difficult to understand the high price of most highly improved breeds,
which almost implies long-continued close interbreeding, except on the
belief that this process lessens fertility and increases liability to
distemper and other diseases. A high authority, Mr. Scrope, attributes
the rarity and deterioration in size of the Scotch deerhound (the few
individuals now existing throughout the country being all related) in
large part to close interbreeding.
With all highly-bred animals there is more or less difficulty in getting
them to procreate quickly, and all suffer much from delicacy of
constitution; but I do not pretend that these effects ought to be wholly
attributed to close interbreeding. A great judge of rabbits[260] says, "the
long-eared does are often too highly bred or forced in their youth to be
of much value as breeders, often turning out barren or bad mothers."
Again: "Very long-eared bucks will also sometimes prove barren."
These highly-bred rabbits often desert their young, so that it is
necessary to have nurse-rabbits.
With Pigs there is more unanimity amongst breeders on the evil effects
of close interbreeding than, perhaps, with any other large animal. Mr.
Druce, a great and successful breeder of the Improved Oxfordshires (a
crossed race), writes, "without a change of boars of a different tribe,
but of the same breed, constitution cannot be preserved." Mr. Fisher
Hobbs, the raiser of the celebrated Improved Essex breed, divided his
stock into three separate families, by which means he maintained the
breed for more than twenty years, "by judicious selection from the
three distinct families."[261] Lord Western was the first importer of a
Neapolitan boar and sow. "From this pair he bred in-and-in, until the
breed was in danger of becoming extinct, a sure result (as Mr. Sidney
remarks) of in-and-in breeding." Lord Western then crossed his
Neapolitan pigs with the old Essex, and made the first great step
towards the Improved Essex breed. Here is a more interesting case. Mr.
J. Wright, well known as a breeder, crossed[262] the same boar with the

daughter, granddaughter, and great-granddaughter, and so on for seven
generations. The result was, that in many instances the offspring failed
to breed; in others they produced few that lived; and of the latter many
were idiotic, without sense even to suck, and when attempting to move
could not walk straight. Now it deserves especial notice, that the two
last sows produced by this long course of interbreeding were sent to
other boars, and they bore several litters of healthy pigs. The best sow
in external appearance produced during the whole seven generations
was one in the last stage of descent; but the litter consisted of this one
sow. She would not breed to her sire, yet bred at the first trial to a
stranger in blood. So that, in Mr. Wright's case, long-continued and
extremely close interbreeding did not affect the external form or merit
of the young; but with many of them the general constitution and
mental powers, and especially the reproductive functions, were
seriously affected.

Nathusius gives[263] an analogous and even more striking case: he
imported from England a pregnant sow of the large Yorkshire breed,
and bred the product closely in-and-in for three generations: the result
was unfavourable, as the young were weak in constitution, with
impaired fertility. One of the latest sows, which he esteemed a good
animal, produced, when paired with her own uncle (who was known to
be productive with sows of other breeds), a litter of six, and a second
time a litter of only five weak young pigs. He then paired this sow with
a boar of a small black breed, which he had likewise imported from
England, and which boar, when matched with sows of his own breed,
produced from seven to nine young: now, the sow of the large breed,
which was so unproductive when paired with her own uncle, yielded to
the small black boar, in the first litter twenty-one, and in the second
litter eighteen young pigs; so that in one year she produced thirty-nine
fine young animals!
As in the case of several other animals already mentioned, even when
no injury is perceptible from moderately close interbreeding, yet, to
quote the words of Mr. Coate, a most successful breeder (who five
times won the annual gold medal of the Smithfield Club Show for the
best pen of pigs), "Crosses answer well for profit to the farmer, as you
get more constitution and quicker growth; but for me, who sell a great

number of pigs for breeding purposes, I find it will not do, as it
requires many years to get anything like purity of blood again."[264]

Before passing on to Birds, I ought to refer to man, though I am unwilling
to enter on this subject, as it is surrounded by natural prejudices. It has
moreover been discussed by various authors under many points of view.[265]
Mr. Tylor[266] has shown that with widely different races, in the most distant
quarters of the world, marriages between relations—even between distant
relations—have been strictly prohibited. A few exceptional cases can be
specified, especially with royal families; and these have been enlarged on in
a learned article[267] by Mr. W. Adam, and formerly in 1828 by Hofacker.
Mr. Tylor is inclined to believe that the almost universal prohibition of
closely-related marriages has arisen from their evil effects having been
observed, and he ingeniously explains some apparent anomalies in the
prohibition not extending equally to the relations on both the male and
female side. He admits, however, that other causes, such as the extension of
friendly alliances, may have come into play. Mr. W. Adam, on the other
hand, concludes that related marriages are prohibited and viewed with
repugnance from the confusion which would thus arise in the descent of
property, and from other still more recondite reasons; but I cannot accept
this view, seeing that the savages of Australia and South America,[268] who
have no property to bequeath or fine moral feelings to confuse, hold the
crime of incest in abhorrence.
It would be interesting to know, if it could be ascertained, as throwing light
on this question with respect to man, what occurs with the higher
anthropomorphous apes—whether the young males and females soon
wander away from their parents, or whether the old males become jealous
of their sons and expel them, or whether any inherited instinctive feeling,
from being beneficial, has been generated, leading the young males and
females of the same family to prefer pairing with distinct families, and to
dislike pairing with each other. A considerable body of evidence has already
been advanced, showing that the offspring from parents which are not
related are more vigorous and fertile than those from parents which are
closely related; hence any slight feeling, arising from the sexual excitement
of novelty or other cause, which led to the former rather than to the latter
unions, would be augmented through natural selection, and thus might

become instinctive; for those individuals which had an innate preference of
this kind would increase in number. It seems more probable, that degraded
savages should thus unconsciously have acquired their dislike and even
abhorrence of incestuous marriages, rather than that they should have
discovered by reasoning and observation the evil results. The abhorrence
occasionally failing is no valid argument against the feeling being
instinctive, for any instinct may occasionally fail or become vitiated, as
sometimes occurs with parental love and the social sympathies. In the case
of man, the question whether evil follows from close interbreeding will
probably never be answered by direct evidence, as he propagates his kind so
slowly and cannot be subjected to experiment; but the almost universal
practice of all races at all times of avoiding closely-related marriages is an
argument of considerable weight; and whatever conclusion we arrive at in
regard to the higher animals may be safely extended to man.

Turning now to Birds: in the case of the Fowl a whole array of
authorities could be given against too close interbreeding. Sir J.
Sebright positively asserts that he made many trials, and that his fowls,
when thus treated, became long in the legs, small in the body, and bad
breeders.[269] He produced the famous Sebright Bantams by
complicated crosses, and by breeding in-and-in; and since his time
there has been much close interbreeding with these Bantams; and they
are now notoriously bad breeders. I have seen Silver Bantams, directly
descended from his stock, which had become almost as barren as
hybrids; for not a single chicken had been that year hatched from two
full nests of eggs. Mr. Hewitt says that with these Bantams the sterility
of the male stands, with rare exceptions, in the closest relation with
their loss of certain secondary male characters: he adds, "I have
noticed, as a general rule, that even the slightest deviation from
feminine character in the tail of the male Sebright—say the elongation
by only half an inch of the two principal tail-feathers—brings with it
improved probability of increased fertility."[270]

Mr. Wright states[271] that Mr. Clark, "whose fighting-cocks were so
notorious, continued to breed from his own kind till they lost their
disposition to fight, but stood to be cut up without making any
resistance, and were so reduced in size as to be under those weights

required for the best prizes; but on obtaining a cross from Mr.
Leighton, they again resumed their former courage and weight." It
should be borne in mind that game-cocks before they fought were
always weighed, so that nothing was left to the imagination about any
reduction or increase of weight. Mr. Clark does not seem to have bred
from brothers and sisters, which is the most injurious kind of union;
and he found, after repeated trials, that there was a greater reduction in
weight in the young from a father paired with his daughter, than from a
mother with her son. I may add that Mr. Eyton, of Eyton, the well-
known ornithologist, who is a large breeder of Grey Dorkings, informs
me that they certainly diminish in size, and become less prolific, unless
a cross with another strain is occasionally obtained. So it is with
Malays, according to Mr. Hewitt, as far as size is concerned.[272]

An experienced writer[273] remarks that the same amateur, as is well
known, seldom long maintains the superiority of his birds; and this, he
adds, undoubtedly is due to all his stock "being of the same blood;"
hence it is indispensable that he should occasionally procure a bird of
another strain. But this is not necessary with those who keep a stock of
fowls at different stations. Thus, Mr. Ballance, who has bred Malays
for thirty years, and has won more prizes with these birds than any
other fancier in England, says that breeding in-and-in does not
necessarily cause deterioration; "but all depends upon how this is
managed." "My plan has been to keep about five or six distinct runs,
and to rear about two hundred or three hundred chickens each year,
and select the best birds from each run for crossing. I thus secure
sufficient crossing to prevent deterioration."[274]
We thus see that there is almost complete unanimity with poultry-
breeders that, when fowls are kept at the same place, evil quickly
follows from interbreeding carried on to an extent which would be
disregarded in the case of most quadrupeds. On the other hand, it is a
generally received opinion that cross-bred chickens are the hardiest
and most easily reared.[275] Mr. Tegetmeier, who has carefully attended
to poultry of all breeds, says[276] that Dorking hens, allowed to run
with Houdan or Crevecœur cocks, "produce in the early spring
chickens that for size, hardihood, early maturity, and fitness for the

market, surpass those of any pure breed that we have ever raised." Mr.
Hewitt gives it as a general rule with fowls, that crossing the breed
increases their size. He makes this remark after stating that hybrids
from the pheasant and fowl are considerably larger than either
progenitor: so again, hybrids from the male golden pheasant and hen
common pheasant "are of far larger size than either parent-bird."[277]
To this subject of the increased size of hybrids I shall presently return.
With Pigeons, breeders are unanimous, as previously stated, that it is
absolutely indispensable, notwithstanding the trouble and expense thus
caused, occasionally to cross their much-prized birds with individuals
of another strain, but belonging, of course, to the same variety. It
deserves notice that, when large size is one of the desired characters, as
with pouters,[278] the evil effects of close interbreeding are much
sooner perceived than when small birds, such as short-faced tumblers,
are valued. The extreme delicacy of the high fancy breeds, such as
these tumblers and improved English carriers, is remarkable; they are
liable to many diseases, and often die in the egg or during the first
moult; and their eggs have generally to be hatched under foster-
mothers. Although these highly-prized birds have invariably been
subjected to much close interbreeding, yet their extreme delicacy of
constitution cannot perhaps be thus fully explained. Mr. Yarrell
informed me that Sir J. Sebright continued closely interbreeding some
owl-pigeons, until from their extreme sterility he as nearly as possible
lost the whole family. Mr. Brent[279] tried to raise a breed of
trumpeters, by crossing a common pigeon, and recrossing the daughter,
granddaughter, great-granddaughter, and great-great-granddaughter,
with the same male trumpeter, until he obtained a bird with 15/16ths of
trumpeter's blood; but then the experiment failed, for "breeding so
close stopped reproduction." The experienced Neumeister[280] also
asserts that the offspring from dovecotes and various other breeds are
"generally very fertile and hardy birds:" so again, MM. Boitard and
Corbié,[281] after forty-five years' experience, recommend persons to
cross their breeds for amusement; for, if they fail to make interesting
birds, they will succeed under an economical point of view, "as it is
found that mongrels are more fertile than pigeons of pure race."

I will refer only to one other animal, namely, the Hive-bee, because a
distinguished entomologist has advanced this as a case of inevitable
close interbreeding. As the hive is tenanted by a single female, it might
have been thought that her male and female offspring would always
have bred together, more especially as bees of different hives are
hostile to each other; a strange worker being almost always attacked
when trying to enter another hive. But Mr. Tegetmeier has shown[282]
that this instinct does not apply to drones, which are permitted to enter
any hive; so that there is no à priori improbability of a queen receiving
a foreign drone. The fact of the union invariably and necessarily taking
place on the wing, during the queen's nuptial flight, seems to be a
special provision against continued interbreeding. However this may
be, experience has shown, since the introduction of the yellow-banded
Ligurian race into Germany and England, that bees freely cross: Mr.
Woodbury, who introduced Ligurian bees into Devonshire, found
during a single season that three stocks, at distances of from one to two
miles from his hives, were crossed by his drones. In one case the
Ligurian drones must have flown over the city of Exeter, and over
several intermediate hives. On another occasion several common black
queens were crossed by Ligurian drones at a distance of from one to
three and a half miles.[283]

Plants.

When a single plant of a new species is introduced into any country, if
propagated by seed, many individuals will soon be raised, so that if the
proper insects be present there will be crossing. With newly-introduced
trees or other plants not propagated by seed we are not here concerned.
With old-established plants it is an almost universal practice
occasionally to make exchanges of seed, by which means individuals
which have been exposed to different conditions of life,—and this, as
we have seen, diminishes the evil from close interbreeding,—will
occasionally be introduced into each district.
Experiments have not been tried on the effects of fertilising flowers
with their own pollen during several generations. But we shall
presently see that certain plants, either normally or abnormally, are

more or less sterile, even in the first generation, when fertilised by
their own pollen. Although nothing is directly known on the evil
effects of long-continued close interbreeding with plants, the converse
proposition that great good is derived from crossing is well established.
With respect to the crossing of individuals belonging to the same sub-
variety, Gärtner, whose accuracy and experience exceeded that of all
other hybridisers, states[284] that he has many times observed good
effects from this step, especially with exotic genera, of which the
fertility is somewhat impaired, such as Passiflora, Lobelia, and
Fuchsia. Herbert also says,[285] "I am inclined to think that I have
derived advantage from impregnating the flower from which I wished
to obtain seed with pollen from another individual of the same variety,
or at least from another flower, rather than with its own." Again,
Professor Lecoq asserts that he has ascertained that crossed offspring
are more vigorous and robust than their parents.[286]
General statements of this kind, however, can seldom be fully trusted;
consequently I have begun a series of experiments, which, if they
continue to give the same results as hitherto, will for ever settle the
question of the good effects of crossing two distinct plants of the same
variety, and of the evil effects of self-fertilisation. A clear light will
thus also be thrown on the fact that flowers are invariably constructed
so as to permit, or favour, or necessitate the union of two individuals.
We shall clearly understand why monœcious and diœcious,—why
dimorphic and trimorphic plants exist, and many other such cases. The
plan which I have followed in my experiments is to grow plants in the
same pot, or in pots of the same size, or close together in the open
ground; to carefully exclude insects; and then to fertilise some of the
flowers with pollen from the same flower, and others on the same plant
with pollen from a distinct but adjoining plant. In many, but not all, of
these experiments, the crossed plants yielded much more seed than the
self-fertilised plants; and I have never seen the reversed case. The self-
fertilised and crossed seeds thus obtained were allowed to germinate in
the same glass vessel on damp sand; and as the seeds successively
germinated, they were planted in pairs on opposite sides of the same
pot, with a superficial partition between them, and were placed so as to

be equally exposed to the light. In other cases the self-fertilised and
crossed seeds were simply sown on opposite sides of the same small
pot. I have, in short, followed different plans, but in every case have
taken all the precautions which I could think of, so that the two lots
should be equally favoured. Now, I have carefully observed the growth
of plants raised from crossed and self-fertilised seed, from their
germination to maturity, in species of the following genera, namely,
Brassica, Lathyrus, Lupinus, Lobelia, Lactuca, Dianthus, Myosotis,
Petunia, Linaria, Calceolaria, Mimulus, and Ipomœa, and the
difference in their powers of growth, and of withstanding in certain
cases unfavourable conditions, was most manifest and strongly
marked. It is of importance that the two lots of seed should be sown or
planted on opposite sides of the same pot, so that the seedlings may
struggle against each other; for if sown separately in ample and good
soil, there is often but little difference in their growth.
I will briefly describe the two most striking cases as yet observed by
me. Six crossed and six self-fertilised seeds of Ipomœa purpurea, from
plants treated in the manner above described, were planted as soon as
they had germinated, in pairs on opposite sides of two pots, and rods of
equal thickness were given them to twine up. Five of the crossed plants
grew from the first more quickly than the opposed self-fertilised
plants; the sixth, however, was weakly and was for a time beaten, but
at last its sounder constitution prevailed and it shot ahead of its
antagonist. As soon as each crossed plant reached the top of its seven-
foot rod its fellow was measured, and the result was that, when the
crossed plants were seven feet high, the self-fertilised had attained the
average height of only five feet four and a half inches. The crossed
plants flowered a little before, and more profusely than the self-
fertilised plants. On opposite sides of another small pot a large number
of crossed and self-fertilised seeds were sown, so that they had to
struggle for bare existence; a single rod was given to each lot: here
again the crossed plants showed from the first their advantage; they
never quite reached the summit of the seven-foot rod, but relatively to
the self-fertilised plants their average height was as seven feet to five
feet two inches. The experiment was repeated in the two following
generations with plants raised from the self-fertilised and crossed

plants, treated in exactly the same manner, and with nearly the same
result. In the second generation, the crossed plants, which were again
crossed, produced 121 seed-capsules, whilst the self-fertilised plants,
again self-fertilised, produced only 84 capsules.
Some flowers of the Mimulus luteus were fertilised with their own
pollen, and others were crossed with pollen from distinct plants
growing in the same pot. The seeds after germinating were thickly
planted on opposite sides of a pot. The seedlings were at first equal in
height; but when the young crossed plants were exactly half an inch,
the self-fertilised plants were only a quarter of an inch high. But this
inequality did not continue, for, when the crossed plants were four and
a half inches high, the self-fertilised were three inches; and they
retained the same relative difference till their growth was complete.
The crossed plants looked far more vigorous than the uncrossed, and
flowered before them; they produced also a far greater number of
flowers, which yielded capsules (judging, however, from only a few)
containing more seeds. As in the former case, the experiment was
repeated in the same manner during the next two generations, and with
exactly the same result. Had I not watched these plants of the Mimulus
and Ipomœa during their whole growth, I could not have believed it
possible, that a difference apparently so slight, as that of the pollen
being taken from the same flower, and from a distinct plant growing in
the same small pot, could have made so wonderful a difference in the
growth and vigour of the plants thus produced. This, under a
physiological point of view, is a most remarkable phenomenon.

With respect to the benefit derived from crossing distinct varieties,
plenty of evidence has been published. Sageret[287] repeatedly speaks
in strong terms of the vigour of melons raised by crossing different
varieties, and adds that they are more easily fertilised than common
melons, and produce numerous good seed. Here follows the evidence
of an English gardener:[288] "I have this summer met with better
success in my cultivation of melons, in an unprotected state, from the
seeds of hybrids (i.e. mongrels) obtained by cross impregnation, than
with old varieties. The offspring of three different hybridisations (one
more especially, of which the parents were the two most dissimilar

varieties I could select) each yielded more ample and finer produce
than any one of between twenty and thirty established varieties."

Andrew Knight[289] believed that his seedlings from crossed varieties
of the apple exhibited increased vigour and luxuriance; and M.
Chevreul[290] alludes to the extreme vigour of some of the crossed
fruit-trees raised by Sageret.

By crossing reciprocally the tallest and shortest peas, Knight[291] says,
"I had in this experiment a striking instance of the stimulative effects
of crossing the breeds; for the smallest variety, whose height rarely
exceeded two feet, was increased to six feet; whilst the height of the
large and luxuriant kind was very little diminished." Mr. Laxton gave
me seed-peas produced from crosses between four distinct kinds; and
the plants thus raised were extraordinarily vigorous, being in each case
from one to two or three feet taller than the parent-forms growing close
alongside them.

Wiegmann[292] made many crosses between several varieties of
cabbage; and he speaks with astonishment of the vigour and height of
the mongrels, which excited the amazement of all the gardeners who
beheld them. Mr. Chaundy raised a great number of mongrels by
planting together six distinct varieties of cabbage. These mongrels
displayed an infinite diversity of character; "But the most remarkable
circumstance was, that, while all the other cabbages and borecoles in
the nursery were destroyed by a severe winter, these hybrids were little
injured, and supplied the kitchen when there was no other cabbage to
be had."

Mr. Maund exhibited before the Royal Agricultural Society[293]
specimens of crossed wheat, together with their parent varieties; and
the editor states that they were intermediate in character, "united with
that greater vigour of growth, which it appears, in the vegetable as in
the animal world, is the result of a first cross." Knight also crossed
several varieties of wheat,[294] and he says "that in the years 1795 and
1796, when almost the whole crop of corn in the island was blighted,
the varieties thus obtained, and these only, escaped in this
neighbourhood, though sown in several different soils and situations."

Here is a remarkable case: M. Clotzsch[295] crossed Pinus sylvestris
and nigricans, Quercus robur and pedunculata, Alnus glutinosa and
incana, Ulmus campestris and effusa; and the cross-fertilised seeds, as
well as seeds of the pure parent-trees, were all sown at the same time
and in the same place. The result was, that after an interval of eight
years, the hybrids were one-third taller than the pure trees!

The facts above given refer to undoubted varieties, excepting the trees
crossed by Clotzsch, which are ranked by various botanists as strongly-
marked races, sub-species, or species. That true hybrids raised from
entirely distinct species, though they lose in fertility, often gain in size
and constitutional vigour, is certain. It would be superfluous to quote
any facts; for all experimenters, Kölreuter, Gärtner, Herbert, Sageret,
Lecoq, and Naudin, have been struck with the wonderful vigour,
height, size, tenacity of life, precocity, and hardiness of their hybrid
productions. Gärtner[296] sums up his conviction on this head in the
strongest terms. Kölreuter[297] gives numerous precise measurements
of the weight and height of his hybrids in comparison with
measurements of both parent-forms; and speaks with astonishment of
their "statura portentosa," their "ambitus vastissimus ac altitudo valde
conspicua." Some exceptions to the rule in the case of very sterile
hybrids have, however, been noticed by Gärtner and Herbert; but the
most striking exceptions are given by Max Wichura,[298] who found
that hybrid willows were generally tender in constitution, dwarf, and
short-lived.
Kölreuter explains the vast increase in the size of the roots, stems, &c.,
of his hybrids, as the result of a sort of compensation due to their
sterility, in the same way as many emasculated animals are larger than
the perfect males. This view seems at first sight extremely probable,
and has been accepted by various authors;[299] but Gärtner[300] has well
remarked that there is much difficulty in fully admitting it; for with
many hybrids there is no parallelism between the degree of their
sterility and their increased size and vigour. The most striking
instances of luxuriant growth have been observed with hybrids which
were not sterile in any extreme degree. In the genus Mirabilis, certain

hybrids are unusually fertile, and their extraordinary luxuriance of
growth, together with their enormous roots,[301] have been transmitted
to their progeny. The increased size of the hybrids produced between
the fowl and pheasant, and between the distinct species of pheasants,
has been already noticed. The result in all cases is probably in part due
to the saving of nutriment and vital force through the sexual organs not
acting, or acting imperfectly, but more especially to the general law of
good being derived from a cross. For it deserves especial attention that
mongrel animals and plants, which are so far from being sterile that
their fertility is often actually augmented, have, as previously shown,
their size, hardiness, and constitutional vigour generally increased. It is
not a little remarkable that an accession of vigour and size should thus
arise under the opposite contingencies of increased and diminished
fertility.

It is a perfectly well ascertained fact[302] that hybrids will invariably
breed more readily with either pure parent, and not rarely with a
distinct species, than with each other. Herbert is inclined to explain
even this fact by the advantage derived from a cross; but Gärtner more
justly accounts for it by the pollen of the hybrid, and probably its
ovules, being in some degree vitiated, whereas the pollen and ovules of
both pure parents and of any third species are sound. Nevertheless
there are some well-ascertained and remarkable facts, which, as we
shall immediately see, show that the act of crossing in itself
undoubtedly tends to increase or re-establish the fertility of hybrids.

On certain Hermaphrodite Plants which, either normally or abnormally,
require to be fertilised by pollen from a distinct individual or species.
The facts now to be given differ from those hitherto detailed, as the self-
sterility does not here result from long-continued, close interbreeding.
These facts are, however, connected with our present subject, because a
cross with a distinct individual is shown to be either necessary or
advantageous. Dimorphic and trimorphic plants, though they are
hermaphrodites, must be reciprocally crossed, one set of forms by the other,
in order to be fully fertile, and in some cases to be fertile in any degree. But
I should not have noticed these plants, had it not been for the following
cases given by Dr. Hildebrand:[303]—

Primula sinensis is a reciprocally dimorphic species: Dr. Hildebrand
fertilised twenty-eight flowers of both forms, each by pollen of the
other form, and obtained the full number of capsules containing on an
average 42.7 seed per capsule; here we have complete and normal
fertility. He then fertilised forty-two flowers of both forms with pollen
of the same form, but taken from a distinct plant, and all produced
capsules containing on an average only 19.6 seed. Lastly, and here we
come to our more immediate point, he fertilised forty-eight flowers of
both forms with pollen of the same form, taken from the same flower,
and now he obtained only thirty-two capsules, and these contained on
an average 18.6 seed, or one less per capsule than in the former case.
So that, with these illegitimate unions, the act of impregnation is less
assured, and the fertility slightly less, when the pollen and ovules
belong to the same flower, than when belonging to two distinct
individuals of the same form. Dr. Hildebrand has recently made
analogous experiments on the long-styled form of Oxalis rosea, with
the same result.[304]

It has recently been discovered that certain plants, whilst growing in their
native country under natural conditions, cannot be fertilised with pollen
from the same plant. They are sometimes so utterly self-impotent, that,
though they can readily be fertilised by the pollen of a distinct species or
even distinct genus, yet, wonderful as the fact is, they never produce a
single seed by their own pollen. In some cases, moreover, the plant's own
pollen and stigma mutually act on each other in a deleterious manner. Most
of the facts to be given relate to Orchids, but I will commence with a plant
belonging to a widely different family.

Sixty-three flowers of Corydalis cava, borne on distinct plants, were
fertilised by Dr. Hildebrand[305] with pollen from other plants of the
same species; and fifty-eight capsules were obtained, including on an
average 4.5 seed in each. He then fertilised sixteen flowers produced
by the same raceme, one with another, but obtained only three
capsules, one of which alone contained any good seeds, namely, two in
number. Lastly, he fertilised twenty-seven flowers, each with its own
pollen; he left also fifty-seven flowers to be spontaneously fertilised,
and this would certainly have ensued if it had been possible, for the

anthers not only touch the stigma, but the pollen-tubes were seen by
Dr. Hildebrand to penetrate it; nevertheless these eighty-four flowers
did not produce a single seed-capsule! This whole case is highly
instructive, as it shows how widely different the action of the same
pollen is, according as it is placed on the stigma of the same flower, or
on that of another flower on the same raceme, or on that of a distinct
plant.
With exotic Orchids several analogous cases have been observed,
chiefly by Mr. John Scott.[306] Oncidium sphacelatum has effective
pollen, for with it Mr. Scott fertilised two distinct species; its ovules
are likewise capable of impregnation, for they were readily fertilised
by the pollen of O. divaricatum; nevertheless, between one and two
hundred flowers fertilised by their own pollen did not produce a single
capsule, though the stigmas were penetrated by the pollen-tubes. Mr.
Robinson Munro, of the Royal Botanic Gardens of Edinburgh, also
informs me (1864) that a hundred and twenty flowers of this same
species were fertilised by him with their own pollen, and did not
produce a capsule, but eight flowers fertilised by the pollen of O.
divaricatum produced four fine capsules: again, between two and three
hundred flowers of O. divaricatum, fertilised by their own pollen, did
not set a capsule, but twelve flowers fertilised by O. flexuosum
produced eight fine capsules: so that here we have three utterly self-
impotent species, with their male and female organs perfect, as shown
by their mutual fertilisation. In these cases fertilisation was effected
only by the aid of a distinct species. But, as we shall presently see,
distinct plants, raised from seed, of Oncidium flexuosum, and probably
of the other species, would have been perfectly capable of fertilising
each other, for this is the natural process. Again, Mr. Scott found that
the pollen of a plant of O. microchilum was good, for with it he
fertilised two distinct species; he found its ovules good, for they could
be fertilised by the pollen of one of these species, and by the pollen of
a distinct plant of O. microchilum; but they could not be fertilised by
pollen of the same plant, though the pollen-tubes penetrated the
stigma. An analogous case has been recorded by M. Rivière,[307] with
two plants of O. Cavendishianum, which were both self-sterile, but
reciprocally fertilised each other. All these cases refer to the genus

Oncidium, but Mr. Scott found that Maxillaria atro-rubens was "totally
insusceptible of fertilisation with its own pollen," but fertilised, and
was fertilised by, a widely distinct species, viz. M. squalens.
As these orchids had grown under unnatural conditions, in hot-houses,
I concluded without hesitation that their self-sterility was due to this
cause. But Fritz Müller informs me that at Desterro, in Brazil, he
fertilised above one hundred flowers of the above-mentioned
Oncidium flexuosum, which is there endemic, with its own pollen, and
with that taken from distinct plants; all the former were sterile, whilst
those fertilised by pollen from any other plant of the same species
were fertile. During the first three days there was no difference in the
action of the two kinds of pollen: that placed on the stigma of the same
plant separated in the usual manner into grains, and emitted tubes
which penetrated the column, and the stigmatic chamber shut itself; but
the flowers alone which had been fertilised by pollen taken from a
distinct plant produced seed-capsules. On a subsequent occasion these
experiments were repeated on a large scale with the same result. Fritz
Müller found that four other endemic species of Oncidium were in like
manner utterly sterile with their own pollen, but fertile with that from
any other plant: some of them likewise produced seed-capsules when
impregnated with pollen of widely distinct genera, such as Leptotes,
Cyrtopodium, and Rodriguezia! Oncidium crispum, however, differs
from the foregoing species in varying much in its self-sterility; some
plants producing fine pods with their own pollen, others failing to do
so; in two or three instances, Fritz Müller observed that the pods
produced by pollen taken from a distinct flower on the same plant,
were larger than those produced by the flower's own pollen. In
Epidendrum cinnabarinum, an orchid belonging to another division of
the family, fine pods were produced by the plant's own pollen, but they
contained by weight only about half as much seed as the capsules
which had been fertilized by pollen from a distinct plant, and in one
instance from a distinct species; moreover, a very large proportion, and
in some cases nearly all the seed produced by the plant's own pollen,
was embryonless and worthless. Some self-fertilized capsules of a
Maxillaria were in a similar state.

Another observation made by Fritz Müller is highly remarkable,
namely, that with various orchids the plant's own pollen not only fails
to impregnate the flower, but acts on the stigma, and is acted on, in an
injurious or poisonous manner. This is shown by the surface of the
stigma in contact with the pollen, and by the pollen itself, becoming in
from three to five days dark brown, and then decaying. The
discolouration and decay are not caused by parasitic cryptogams,
which were observed by Fritz Müller in only a single instance. These
changes are well shown by placing on the same stigma, at the same
time, the plant's own pollen and that from a distinct plant of the same
species, or of another species, or even of another and widely remote
genus. Thus, on the stigma of Oncidium flexuosum, the plant's own
pollen and that from a distinct plant were placed side by side, and in
five days' time the latter was perfectly fresh, whilst the plant's own
pollen was brown. On the other hand, when the pollen of a distinct
plant of the Oncidium flexuosum, and of the Epidendrum zebra (nov.
spec.?), were placed together on the same stigma, they behaved in
exactly the same manner, the grains separating, emitting tubes, and
penetrating the stigma, so that the two pollen-masses, after an interval
of eleven days, could not be distinguished except by the difference of
their caudicles, which, of course, undergo no change. Fritz Müller has,
moreover, made a large number of crosses between orchids belonging
to distinct species and genera, and he finds that in all cases when the
flowers are not fertilised their footstalks first begin to wither; and the
withering slowly spreads upwards until the germens fall off, after an
interval of one or two weeks, and in one instance of between six and
seven weeks; but even in this latter case, and in most other cases, the
pollen and stigma remained in appearance fresh. Occasionally,
however, the pollen becomes brownish, generally on the external
surface, and not in contact with the stigma, as is invariably the case
when the plant's own pollen is applied.
Fritz Müller observed the poisonous action of the plant's own pollen in
the above-mentioned Oncidium flexuosum, O. unicorne, pubes (?), and
in two other unnamed species. Also in two species of Rodriguezia, in
two of Notylia, in one of Burlingtonia, and of a fourth genus in the
same group. In all these cases, except the last, it was proved that the

flowers were, as might have been expected, fertile with pollen from a
distinct plant of the same species. Numerous flowers of one species of
Notylia were fertilized with pollen from the same raceme; in two days'
time they all withered, the germens began to shrink, the pollen-masses
became dark brown, and not one pollen-grain emitted a tube. So that in
this orchid the injurious action of the plant's own pollen is more rapid
than with Oncidium flexuosum. Eight other flowers on the same
raceme were fertilized with pollen from a distinct plant of the same
species: two of these were dissected, and their stigmas were found to
be penetrated by numberless pollen-tubes; and the germens of the other
six flowers became well developed. On a subsequent occasion many
other flowers were fertilized with their own pollen, and all fell off dead
in a few days; whilst some flowers on the same raceme which had been
left simply unfertilised adhered and long remained fresh. We have seen
that in cross-unions between extremely distinct orchids the pollen long
remains undecayed; but Notylia behaved in this respect differently; for
when its pollen was placed on the stigma of Oncidium flexuosum, both
the stigma and pollen quickly became dark brown, in the same manner
as if the plant's own pollen had been applied.
Fritz Müller suggests that, as in all these cases the plant's own pollen is
not only impotent (thus effectually preventing self-fertilization), but
likewise prevents, as was ascertained in the case of the Notylia and
Oncidium flexuosum, the action of subsequently applied pollen from a
distinct individual, it would be an advantage to the plant to have its
own pollen rendered more and more deleterious; for the germens
would thus quickly be killed, and, dropping off, there would be no
further waste in nourishing a part which ultimately could be of no
avail. Fritz Müller's discovery that a plant's own pollen and stigma in
some cases act on each other as if mutually poisonous, is certainly
most remarkable.

We now come to cases closely analogous with those just given, but
different, inasmuch as individual plants alone of the species are self-
impotent. This self-impotence does not depend on the pollen or ovules
being in a state unfit for fertilisation, for both have been found effective in
union with other plants of the same or of a distinct species. The fact of these
plants having spontaneously acquired so peculiar a constitution, that they

can be fertilised more readily by the pollen of a distinct species than by
their own, is remarkable. These abnormal cases, as well as the foregoing
normal cases, in which certain orchids, for instance, can be much more
easily fertilised by the pollen of a distinct species than by their own, are
exactly the reverse of what occurs with all ordinary species. For in these
latter the two sexual elements of the same individual plant are capable of
freely acting on each other; but are so constituted that they are more or less
impotent when brought into union with the sexual elements of a distinct
species, and produce more or less sterile hybrids. It would appear that the
pollen or ovules, or both, of the individual plants which are in this abnormal
state, have been affected in some strange manner by the conditions to which
they themselves or their parents have been exposed; but whilst thus
rendered self-sterile, they have retained the capacity common to most
species of partially fertilizing and being partially fertilized by allied forms.
However this may be, the subject, to a certain extent, is related to our
general conclusion that good is derived from the act of crossing.

Gärtner experimented on two plants of Lobelia fulgens, brought from
separate places, and found[308] that their pollen was good, for he
fertilised with it L. cardinalis and syphilitica; their ovules were
likewise good, for they were fertilised by the pollen of these same two
species; but these two plants of L. fulgens could not be fertilised by
their own pollen, as can generally be effected with perfect ease with
this species. Again, the pollen of a plant of Verbascum nigrum grown
in a pot was found by Gärtner[309] capable of fertilising V. lychnitis and
V. Austriacum; the ovules could be fertilised by the pollen of V.
thapsus; but the flowers could not be fertilised by their own pollen.
Kölreuter, also,[310] gives the case of three garden plants of Verbascum
phœniceum, which bore during two years many flowers; these he
successfully fertilised by the pollen of no less than four distinct
species, but they produced not a seed with their own apparently good
pollen; subsequently these same plants, and others raised from seed,
assumed a strangely fluctuating condition, being temporarily sterile on
the male or female side, or on both sides, and sometimes fertile on both
sides; but two of the plants were perfectly fertile throughout the
summer.

It appears[311] that certain flowers on certain plants of Lilium candidum
can be fertilised more easily by pollen from a distinct individual than
by their own. So, again, with the varieties of the potato. Tinzmann,[312]
who made many trials with this plant, says that pollen from another
variety sometimes "exerts a powerful influence, and I have found sorts
of potatoes which would not bear seed from impregnation with the
pollen of their own flowers, would bear it when impregnated with
other pollen." It does not, however, appear to have been proved that the
pollen which failed to act on the flower's own stigma was in itself
good.
In the genus Passiflora it has long been known that several species do
not produce fruit, unless fertilised by pollen taken from distinct
species: thus, Mr. Mowbray[313] found that he could not get fruit from
P. alata and racemosa except by reciprocally fertilising them with each
other's pollen. Similar facts have been observed in Germany and
France;[314] and I have received two authentic accounts of P.
quadrangularis, which never produced fruit with its own pollen, but
would do so freely when fertilised in one case with the pollen of P.
cœrulea, and in another case with that of P. edulis. So again, with
respect to P. laurifolia, a cultivator of much experience has recently
remarked[315] that the flowers "must be fertilised with the pollen of P.
cœrulea, or of some other common kind, as their own pollen will not
fertilise them." But the fullest details on this subject have been given
by Mr. Scott:[316] plants of Passiflora racemosa, cœrulea, and alata
flowered profusely during many years in the Botanic Gardens of
Edinburgh, and, though repeatedly fertilised by Mr. Scott and by others
with their own pollen, never produced any seed; yet this occurred at
once with all three species when they were crossed together in various
ways. But in the case of P. cœrulea, three plants, two of which grew in
the Botanic Gardens, were all rendered fertile, merely by impregnating
the one with pollen of the other. The same result was attained in the
same manner with P. alata, but only with one plant out of three. As so
many self-sterile species have been mentioned, it may be stated that in
the case of P. gracilis, which is an annual, the flowers are nearly as
fertile with their own pollen as with that from a distinct plant; thus
sixteen flowers spontaneously self-fertilised produced fruit, each

containing on an average 21.3 seed, whilst fruit from fourteen crossed
flowers contained 24.1 seed.
Returning to P. alata, I have received (1866) some interesting details
from Mr. Robinson Munro. Three plants, including one in England,
have already been mentioned which were inveterately self-sterile, and
Mr. Munro informs me of several others which, after repeated trials
during many years, have been found in the same predicament. At some
other places, however, this species fruits readily when fertilised with
its own pollen. At Taymouth Castle there is a plant which was formerly
grafted by Mr. Donaldson on a distinct species, name unknown, and
ever since the operation it has produced fruit in abundance by its own
pollen; so that this small and unnatural change in the state of this plant
has restored its self-fertility! Some of the seedlings from the Taymouth
Castle plant were found to be not only sterile with their own pollen,
but with each other's pollen, and with the pollen of distinct species.
Pollen from the Taymouth plant failed to fertilise certain plants of the
same species, but was successful on one plant in the Edinburgh
Botanic Gardens. Seedlings were raised from this latter union, and
some of their flowers were fertilised by Mr. Munro with their own
pollen; but they were found to be as self-impotent as the mother-plant
had always proved, except when fertilised by the grafted Taymouth
plant, and except, as we shall see, when fertilised by her own
seedlings. For Mr. Munro fertilised eighteen flowers on the self-
impotent mother-plant with pollen from these her own self-impotent
seedlings, and obtained, remarkable as the fact is, eighteen fine
capsules full of excellent seed! I have met with no case in regard to
plants which shows so well as this of P. alata, on what small and
mysterious causes complete fertility or complete sterility depends.

The facts hitherto given relate to the much-lessened or completely
destroyed fertility of pure species when impregnated with their own pollen,
in comparison with their fertility when impregnated by distinct individuals
or distinct species; but closely analogous facts have been observed with
hybrids.

Herbert states[317] that having in flower at the same time nine hybrid
Hippeastrums, of complicated origin, descended from several species,

he found that "almost every flower touched with pollen from another
cross produced seed abundantly, and those which were touched with
their own pollen either failed entirely, or formed slowly a pod of
inferior size, with fewer seeds." In the 'Horticultural Journal' he adds
that, "the admission of the pollen of another cross-bred Hippeastrum
(however complicated the cross) to any one flower of the number, is
almost sure to check the fructification of the others." In a letter written
to me in 1839, Dr. Herbert says that he had already tried these
experiments during five consecutive years, and he subsequently
repeated them, with the same invariable result. He was thus led to
make an analogous trial on a pure species, namely, on the Hippeastrum
aulicum, which he had lately imported from Brazil: this bulb produced
four flowers, three of which were fertilised by their own pollen, and
the fourth by the pollen of a triple cross between H. bulbulosum,
reginæ, and vittatum; the result was, that "the ovaries of the three first
flowers soon ceased to grow, and after a few days perished entirely:
whereas the pod impregnated by the hybrid made vigorous and rapid
progress to maturity, and bore good seed, which vegetated freely." This
is, indeed, as Herbert remarks, "a strange truth," but not so strange as it
then appeared.
As a confirmation of these statements, I may add that Mr. M. Mayes,
[318] after much experience in crossing the species of Amaryllis

(Hippeastrum), says, "neither the species nor the hybrids will, we are
well aware, produce seed so abundantly from their own pollen as from
that of others." So, again, Mr. Bidwell, in New South Wales,[319]
asserts that Amaryllis belladonna bears many more seeds when
fertilised by the pollen of Brunswigia (Amaryllis of some authors)
Josephinæ or of B. multiflora, than when fertilised by its own pollen.
Mr. Beaton dusted four flowers of a Cyrtanthus with their own pollen,
and four with the pollen of Vallota (Amaryllis) purpurea; on the
seventh day "those which received their own pollen slackened their
growth, and ultimately perished; those which were crossed with the
Vallota held on."[320] These latter cases, however, relate to uncrossed
species, like those before given with respect to Passiflora, Orchids,
&c., and are here referred to only because the plants belong to the
same group of Amaryllidaceæ.

In the experiments on the hybrid Hippeastrums, if Herbert had found
that the pollen of two or three kinds alone had been more efficient on
certain kinds than their own pollen, it might have been argued that
these, from their mixed parentage, had a closer mutual affinity than the
others; but this explanation is inadmissible, for the trials were made
reciprocally backwards and forwards on nine different hybrids; and a
cross, whichever way taken, always proved highly beneficial. I can add
a striking and analogous case from experiments made by the Rev. A.
Rawson, of Bromley Common, with some complex hybrids of
Gladiolus. This skilful horticulturist possessed a number of French
varieties, differing from each other only in the colour and size of the
flowers, all descended from Gandavensis, a well-known old hybrid,
said to be descended from G. Natalensis by the pollen of G.
oppositiflorus.[321] Mr. Rawson, after repeated trials, found that none
of the varieties would set seed with their own pollen, although taken
from distinct plants of the same variety, which had, of course, been
propagated by bulbs, but that they all seeded freely with pollen from
any other variety. To give two examples: Ophir did not produce a
capsule with its own pollen, but when fertilised with that of Janire,
Brenchleyensis, Vulcain, and Linné, it produced ten fine capsules; but
the pollen of Ophir was good, for when Linné was fertilised by it seven
capsules were produced. This later variety, on the other hand, was
utterly barren with its own pollen, which we have seen was perfectly
efficient on Ophir. Altogether, Mr. Rawson, in the year 1861, fertilised
twenty-six flowers borne by four varieties with pollen taken from other
varieties, and every single flower produced a fine seed-capsule;
whereas fifty-two flowers on the same plants, fertilised at the same
time with their own pollen, did not yield a single seed-capsule. Mr.
Rawson fertilised, in some cases, the alternate flowers, and in other
cases all those down one side of the spike, with pollen of other
varieties, and the remaining flowers with their own pollen; I saw these
plants when the capsules were nearly mature, and their curious
arrangement at once brought full conviction to the mind that an
immense advantage had been derived from crossing these hybrids.
Lastly, I have heard from Dr. E. Bornet, of Antibes, who has made
numerous experiments in crossing the species of Cistus, but as not yet

published the results, that, when any of these hybrids are fertile, they
may be said to be, in regard to function, diœcious; "for the flowers are
always sterile when the pistil is fertilised by pollen taken from the
same flower or from flowers on the same plant. But they are often
fertile if pollen be employed from a distinct individual of the same
hybrid nature, or from a hybrid made by a reciprocal cross."

Conclusion.—The facts just given, which show that certain plants are self-
sterile, although both sexual elements are in a fit state for reproduction
when united with distinct individuals of the same or other species, appear at
first sight opposed to all analogy. The sexual elements of the same flower
have become, as already remarked, differentiated in relation to each other,
almost like those of two distinct species.
With respect to the species which, whilst living under their natural
conditions, have their reproductive organs in this peculiar state, we may
conclude that it has been naturally acquired for the sake of effectually
preventing self-fertilisation. The case is closely analous with dimorphic and
trimorphic plants, which can be fully fertilised only by plants belong to the
opposite form, and not, as in the foregoing cases, in differently by any other
plant. Some of these dimorphic plants are completely sterile with pollen
taken from the same plant or from the same form. It is interesting to observe
the graduated series from plants which, when fertilised by their own pollen,
yield the full number of seed, but with the seedlings a little dwarfed in
stature—to plants which when self-fertilised yield few seeds—to those with
yield none—and, lastly, to those in which the plant's own pollen and stigma
act on each other like poison. This peculiar state of the reproductive organs,
when occurring in certain individuals alone, is evidently abnormal; and as it
chiefly affects exotic plants, or indigenous plants cultivated in pots, we may
attribute it to some change in the conditions of life, acting on the plants
themselves or on their parents. The self-impotent Passiflora alata, which
recovered its self-fertility after having been grafted on a distinct stock,
shows how small a change is sufficient to act powerfully on the
reproductive system. The possibility of a plant becoming under culture self-
impotent is interesting as throwing light on the occurrence of this same
condition in natural species. A cultivated plant in this state generally
remains so during its whole life; and from this fact we may infer that the
state is probably congenital.

Kölreuter, however, has described some plants of Verbascum which varied
in this respect even during the same season. As in all the normal cases, and
in many, probably in most, of the abnormal cases, any two self-impotent
plants can reciprocally fertilize each other, we may infer that a very slight
difference in the nature of their sexual elements suffices to give fertility; but
in other instances, as with some Passifloras and the hybrid Gladioli, a
greater degree of differentiation appears to be necessary, for with these
plants fertility is gained only by the union of distinct species, or of hybrids
of distinct parentage. These facts all point to the same general conclusion,
namely, that good is derived from a cross between individuals, which either
innately, or from exposure to dissimilar conditions, have come to differ in
sexual constitution.
Exotic animals confined in menageries are sometimes in nearly the same
state as the above-described self-impotent plants; for, as we shall see in the
following chapter, certain monkeys, the larger carnivora, several finches,
geese, and pheasants, cross together, quite as freely as, or even more freely
than, the individuals of the same species breed together. Cases will, also, be
given of sexual incompatibility between certain male and female
domesticated animals, which, nevertheless, are fertile when matched with
any other individual of the same kind.
In the early part of this chapter it was shown that the crossing of distinct
forms, whether closely or distantly allied, gives increased size and
constitutional vigour, and, except in the case of crossed species, increased
fertility, to the offspring. The evidence rests on the universal testimony of
breeders (for it should be observed that I am not here speaking of the evil
results of close interbreeding), and is practically exemplified in the higher
value of cross-bred animals for immediate consumption. The good results
of crossing have also been demonstrated, in the case of some animals and of
numerous plants, by actual weight and measurement. Although animals of
pure blood will obviously be deteriorated by crossing, as far as their
characteristic qualities are concerned, there seems to be no exception to the
rule that advantages of the kind just mentioned are thus gained, even when
there has not been any previous close interbreeding. The rule applies to all
animals, even to cattle and sheep, which can long resist breeding in-and-in
between the nearest blood-relations. It applies to individuals of the same

sub-variety but of distinct families, to varieties or races, to sub-species, as
well as to quite distinct species.
In this latter case, however, whilst size, vigour, precocity, and hardiness are,
with rare exceptions, gained, fertility, in a greater or less degree, is lost; but
the gain cannot be exclusively attributed to the principle of compensation;
for there is no close parallelism between the increased size and vigour of
the offspring and their sterility. Moreover it has been clearly proved that
mongrels which are perfectly fertile gain these same advantages as well as
sterile hybrids.
The evil consequences of long-continued close interbreeding are not so
easily recognised as the good effects from crossing, for the deterioration is
gradual. Nevertheless it is the general opinion of those who have had most
experience, especially with animals which propagate quickly, that evil does
inevitably follow sooner or later, but at different rates with different
animals. No doubt a false belief may widely prevail like a superstition; yet
it is difficult to suppose that so many acute and original observers have all
been deceived at the expense of much cost and trouble. A male animal may
sometimes be paired with his daughter, granddaughter, and so on, even for
seven generations, without any manifest bad result; but the experiment has
never been tried of matching brothers and sisters, which is considered the
closest form of interbreeding, for an equal number of generations. There is
good reason to believe that by keeping the members of the same family in
distinct bodies, especially if exposed to somewhat different conditions of
life, and by occasionally crossing these families, the evil results may be
much diminished, or quite eliminated. These results are loss of
constitutional vigour, size, and fertility; but there is no necessary
deterioration in the general form of the body, or in other good qualities. We
have seen that with pigs first-rate animals have been produced after long-
continued close interbreeding, though they had become extremely infertile
when paired with their near relations. The loss of fertility, when it occurs,
seems never to be absolute, but only relative to animals of the same blood;
so that this sterility is to a certain extent analogous with that of self-
impotent plants which cannot be fertilised by their own pollen, but are
perfectly fertile with pollen of any other plant of the same species. The fact
of infertility of this peculiar nature being one of the results of long-
continued interbreeding, shows that interbreeding does not act merely by

combining and augmenting various morbid tendencies common to both
parents; for animals with such tendencies, if not at the time actually ill, can
generally propagate their kind. Although offspring descended from the
nearest blood-relations are not necessarily deteriorated in structure, yet
some authors[322] believe that they are eminently liable to malformations;
and this is not improbable, as everything which lessens the vital powers acts
in this manner. Instances of this kind have been recorded in the case of pigs,
bloodhounds, and some other animals.
Finally, when we consider the various facts now given which plainly show
that good follows from crossing, and less plainly that evil follows from
close interbreeding, and when we bear in mind that throughout the whole
organic world elaborate provision has been made for the occasional union
of distinct individuals, the existence of a great law of nature is, if not
proved, at least rendered in the highest degree probable; namely, that the
crossing of animals and plants which are not closely related to beach other
is highly beneficial or even necessary, and that interbreeding prolonged
during many generations is highly injurious.

CHAPTER XVIII.

ON THE ADVANTAGES AND DISADVANTAGES OF CHANGED
CONDITIONS OF LIFE: STERILITY FROM VARIOUS CAUSES.

ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OF LIFE
—STERILITY FROM CHANGED CONDITIONS, IN ANIMALS, IN THEIR NATIVE
COUNTRY AND IN MENAGERIES—MAMMALS, BIRDS, AND INSECTS—LOSS OF
SECONDARY SEXUAL CHARACTERS AND OF INSTINCTS—CAUSES OF
STERILITY—STERILITY OF DOMESTICATED ANIMALS FROM CHANGED
CONDITIONS—SEXUAL INCOMPATIBILITY OF INDIVIDUAL ANIMALS—
STERILITY OF PLANTS FROM CHANGED CONDITIONS OF LIFE—
CONTABESCENCE OF THE ANTHERS—MONSTROSITIES AS A CAUSE OF
STERILITY—DOUBLE FLOWERS—SEEDLESS FRUIT—STERILITY FROM THE
EXCESSIVE DEVELOPMENT OF THE ORGANS OF VEGETATION—FROM LONG-
CONTINUED PROPAGATION BY BUDS—INCIPIENT STERILITY THE PRIMARY
CAUSE OF DOUBLE FLOWERS AND SEEDLESS FRUIT.

On the Good derived from slight Changes in the Conditions of Life.—In
considering whether any facts were known which might throw light on the
conclusion arrived at in the last chapter, namely, that benefits ensue from
crossing, and that it is a law of nature that all organic beings should
occasionally cross, it appeared to me probable that the good derived from
slight changes in the conditions of life, from being an analogous
phenomenon, might serve this purpose. No two individuals, and still less no
two varieties, are absolutely alike in constitution and structure; and when
the germ of one is fertilised by the male element of another, we may believe
that it is acted on in a somewhat similar manner as an individual when
exposed to slightly changed conditions. Now, every one must have
observed the remarkable influence on convalescents of a change of
residence, and no medical man doubts the truth of this fact. Small farmers
who hold but little land are convinced that their cattle derive great benefit
from a change of pasture. In the case of plants, the evidence is strong that a
great advantage is derived from exchanging seeds, tubers, bulbs, and
cuttings from one soil or place to another as different as possible.

The belief that plants are thus benefited, whether or not well founded,
has been firmly maintained from the time of Columella, who wrote
shortly after the Christian era, to the present day; and it now prevails in
England, France, and Germany.[323] A sagacious observer, Bradley,
writing in 1724,[324] says, "When we once become Masters of a good
Sort of Seed, we should at least put it into Two or Three Hands, where
the Soils and Situations are as different as possible; and every Year the
Parties should change with one another; by which Means, I find the
Goodness of the Seed will be maintained for several Years. For Want
of this Use many Farmers have failed in their Crops and been great
Losers." He then gives his own practical experience on this head. A
modern writer[325] asserts, "Nothing can be more clearly established in
agriculture than that the continual growth of any one variety in the
same district makes it liable to deterioration either in quality or
quantity." Another writer states that he sowed close together in the
same field two lots of wheat-seed, the product of the same original
stock, one of which had been grown on the same land, and the other at
a distance, and the difference in favour of the crop from the latter seed
was remarkable. A gentleman in Surrey who has long made it his

business to raise wheat to sell for seed, and who has constantly realised
in the market higher prices than others, assures me that he finds it
indispensable continually to change his seed; and that for this purpose
he keeps two farms differing much in soil and elevation.
With respect to the tubers of the potato, I find that at the present day
the practice of exchanging sets is almost everywhere followed. The
great growers of potatoes in Lancashire formerly used to get tubers
from Scotland, but they found that "a change from the moss-lands, and
vice versâ, was generally sufficient." In former times in France the
crop of potatoes in the Vosges had become reduced in the course of
fifty or sixty years in the proportion from 120-150 to 30-40 bushels;
and the famous Oberlin attributed the surprising good which he
effected in large part to changing the sets.[326]

A well-known practical gardener, Mr. Robson[327] positively states that
he has himself witnessed decided advantage from obtaining bulbs of
the onion, tubers of the potato, and various seeds, all of the same kind,
from different soils and distant parts of England. He further states that
with plants propagated by cuttings, as with the Pelargonium, and
especially the Dahlia, manifest advantage is derived from getting plans
of the same variety, which have been cultivated in another place; or,
"where the extent of the place allows, to take cuttings from one
description of soil to plant on another, so as to afford the change that
seems so necessary to the well-being of the plants." He maintains that
after a time an exchange of this nature is "forced on the grower,
whether he be prepared for it or not." Similar remarks have been made
by another excellent gardener, Mr. Fish, namely, that cuttings of the
same variety of Calceolaria, which he obtained from a neighbour,
"showed much greater vigour than some of his own that were treated in
exactly the same manner," and he attributed this solely to his own
plants having become "to a certain extent worn out or tired of their
quarters." Something of this kind apparently occurs in grafting and
budding fruit-trees; for, according to Mr. Abbey, grafts or buds
generally take on a distinct variety or even species, or on a stock
previously grafted, with greater facility than on stocks raised from
seeds of the variety which is to be grafted; and he believes this cannot
be altogether explained by the stocks in question being better adapted

to the soil and climate of the place. It should, however, be added, that
varieties grafted or budded on very distinct kinds, though they may
take more readily and grow at first more vigorously than when grafted
on closely allied stocks, afterwards often become unhealthy.

I have studied M. Tessier's careful and elaborate experiments,[328]
made to disprove the common belief that good is derived from a
change of seed; and he certainly shows that the same seed may with
care be cultivated on the same farm (it is not stated whether on exactly
the same soil) for ten consecutive years without loss. Another excellent
observer, Colonel Le Couteur,[329] has come to the same conclusion;
but then he expressly adds, if the same seed be used, "that which is
grown on land manured from the mixen one year becomes seed for
land prepared with lime, and that again becomes seed for land dressed
with ashes, then for land dressed with mixed manure, and so on." But
this in effect is a systematic exchange of seed, within the limits of the
same farm.

On the whole the belief, which has long been held by many skilful
cultivators, that good follows from exchanging seed, tubers, &c., seems to
be fairly well founded. Considering the small size of most seeds, it seems
hardly credible that the advantage thus derived can be due to the seeds
obtaining in one soil some chemical element deficient in the other soil. As
plants after once germinating naturally become fixed to the same spot, it
might have been anticipated that they would show the good effects of a
change more plainly than animals, which continually wander about; and this
apparently is the case. Life depending on, or consisting in, an incessant play
of the most complex forces, it would appear that their action is in some way
stimulated by slight changes in the circumstances to which each organism is
exposed. All forces throughout nature, as Mr. Herbert Spencer[330] remarks,
tend towards an equilibrium, and for the life of each being it is necessary
that this tendency should be checked. If these views and the foregoing facts
can be trusted, they probably throw light, on the one hand, on the good
effects of crossing the breed, for the germ will be thus slightly modified or
acted on by new forces; and on the other hand, on the evil effects of close
interbreeding prolonged during many generations, during which the germ
will be acted on by a male having almost identically the same constitution.

Sterility from changed Conditions of Life.
I will now attempt to show that animals and plants, when removed from
their natural conditions, are often rendered in some degree infertile or
completely barren; and this occurs even when the conditions have not been
greatly changed. This conclusion is not necessarily opposed to that at which
we have just arrived, namely, that lesser changes of other kinds are
advantageous to organic beings. Our present subject is of some importance,
from having an intimate connexion with the causes of variability. Indirectly
it perhaps bears on the sterility of species when crossed: for as, on the one
hand, slight changes in the conditions of life are favourable to plants and
animals, and the crossing of varieties adds to the size, vigour, and fertility
of their offspring; so, on the other hand, certain other changes in the
conditions of life cause sterility; and as this likewise ensues from crossing
much-modified forms or species, we have a parallel and double series of
facts, which apparently stand in close relation to each other.
It is notorious that many animals, though perfectly tamed, refuse to breed in
captivity. Isidore Geoffroy St. Hilaire[331] consequently has drawn a broad
distinction between tamed animals which will not breed under captivity, and
truly domesticated animals which breed freely—generally more freely, as
shown in the sixteenth chapter, than in a state of nature. It is possible and
generally easy to tame most animals; but experience has shown that it is
difficult to get them to breed regularly, or even at all. I shall discuss this
subject in detail; but will give only those cases which seem most
illustrative. My materials are derived from notices scattered through various
works, and especially from a Report, drawn up for me by the kindness of
the officers of the Zoological Society of London, which has especial value,
as it records all the cases, during nine years from 1838-46, in which the
animals were seen to couple but produced no offspring, as well as the cases
in which they never, as far as known, coupled. This MS. Report I have
corrected by the annual Reports subsequently published. Many facts are
given on the breeding of the animals in that magnificent work, 'Gleanings
from the Menageries of Knowsley Hall,' by Dr. Gray. I made, also,
particular inquiries from the experienced keeper of the birds in the old
Surrey Zoological Gardens. I should premise that a slight change in the
treatment of animals sometimes makes a great difference in their fertility;
and it is probable that the results observed in different menageries would

differ. Indeed some animals in our Zoological Gardens have become more
productive since the year 1846. It is, also, manifest from F. Cuvier's account
of the Jardin des Plantes,[332] that the animals formerly bred much less
freely there than with us; for instance, in the Duck tribe, which is highly
prolific, only one species had at that period produced young.

The most remarkable cases, however, are afforded by animals kept in
their native country, which, though perfectly tamed, quite healthy, and
allowed some freedom, are absolutely incapable of breeding. Rengger,
[333]
who in Paraguay particularly attended to this subject, specifies six
quadrupeds in this condition; and he mentions two or three others
which most rarely breed. Mr. Bates, in his admirable work on the
Amazons, strongly insists on similar cases;[334] and he remarks, that
the fact of thoroughly tamed native mammals and birds not breeding
when kept by the Indians, cannot be wholly accounted for by their
negligence or indifference, for the turkey is valued by them, and the
fowl has been adopted by the remotest tribes. In almost every part of
the world—for instance, in the interior of Africa, and in several of the
Polynesian islands—the natives are extremely fond of taming the
indigenous quadrupeds and birds; but they rarely or never succeed in
getting them to breed.
The most notorious case of an animal not breeding in captivity is that
of the elephant. Elephants are kept in large numbers in their native
Indian home, live to old age, and are vigorous enough for the severest
labour; yet, with one or two exceptions, they have never been known
even to couple, though both males and females have their proper
periodical seasons. If, however, we proceed a little eastward to Ava, we
hear from Mr. Crawfurd[335] that their "breeding in the domestic state,
or at least in the half-domestic state in which the female elephants are
generally kept, is of every-day occurrence;" and Mr. Crawfurd informs
me that he believes that the difference must be attributed solely to the
females being allowed to roam the forests with some degree of
freedom. The captive rhinoceros, on the other hand, seems from
Bishop Heber's account[336] to breed in India far more readily than the
elephant. Four wild species of the horse genus have bred in Europe,
though here exposed to a great change in their natural habits of life; but

the species have generally been crossed one with another. Most of the
members of the pig family breed readily in our menageries: even the
Red River hog (Potamochœrus penicillatus), from the sweltering
plains of West Africa, has bred twice in the Zoological Gardens. Here
also the Peccary (Dicotyles torquatus) has bred several times; but
another species, the D. labiatus, though rendered so tame as to be half-
domesticated, breeds so rarely in its native country of Paraguay, that
according to Rengger[337] the fact requires confirmation. Mr. Bates
remarks that the tapir, though often kept tame in Amazonia by the
Indians, never breeds.
Ruminants generally breed quite freely in England, though brought
from widely different climates, as may be seen in the Annual Reports
of the Zoological Gardens, and in the Gleanings from Lord Derby's
menagerie.
The Carnivora, with the exception of the Plantigrade division,
generally breed (though with capricious exceptions) almost as freely as
ruminants. Many species of Felidæ have bred in various menageries,
although imported from various climates and closely confined. Mr.
Bartlett, the present superintendent of the Zoological Gardens,[338]
remarks that the lion appears to breed more frequently and to bring
forth more young at a birth than any other species of the family. He
adds that the tiger has rarely bred; "but there are several well-
authenticated instances of the female tiger breeding with the lion."
Strange as the fact may appear, many animals under confinement unite
with distinct species and produce hybrids quite as freely as, or even
more freely than, with their own species. On inquiring from Dr.
Falconer and others, it appears that the tiger when confined in India
does not breed, though it has been known to couple. The cheetah (Felis
jubata) has never been known by Mr. Bartlett to breed in England, but
it has bred at Frankfort; nor does it breed in India, where it is kept in
large numbers for hunting; but no pains would be taken to make them
breed, as only those animals which have hunted for themselves in a
state of nature are serviceable and worth training.[339] According to
Rengger, two species of wild cats in Paraguay, though thoroughly
tamed, have never bred. Although so many of the Felidæ breed readily

in the Zoological Gardens, yet conception by no means always follows
union: in the nine-year Report, various species are specified which
were observed to couple seventy-three times, and no doubt this must
have passed many times unnoticed; yet from the seventy-three unions
only fifteen births ensued. The Carnivora in the Zoological Gardens
were formerly less freely exposed to the air and cold than at present,
and this change of treatment, as I was assured by the former
superintendent, Mr. Miller, greatly increased their fertility. Mr. Bartlett,
and there cannot be a more capable judge, says, "it is remarkable that
lions breed more freely in travelling collections than in the Zoological
Gardens; probably the constant excitement and irritation produced by
moving from place to place, or change of air, may have considerable
influence in the matter."
Many members of the Dog family breed readily when confined. The
Dhole is one of the most untameable animals in India, yet a pair kept
there by Dr. Falconer produced young. Foxes, on the other hand, rarely
breed, and I have never heard of such an occurrence with the European
fox: the silver fox of North America (Canis argentatus), however, has
bred several times in the Zoological Gardens. Even the otter has bred
there. Every one knows how readily the semi-domesticated ferret
breeds, though shut up in miserably small cages; but other species of
Viverra and Paradoxurus absolutely refuse to breed in the Zoological
Gardens. The Genetta has bred both here and in the Jardin des Plantes,
and produced hybrids. The Herpestes fasciatus has likewise bred; but I
was formerly assured that the H. griseus, though many were kept in the
Gardens, never bred.
The Plantigrade Carnivora breed under confinement much less freely,
without our being able to assign any reason, than other members of the
group. In the nine-year Report it is stated that the bears had been seen
in the Zoological Gardens to couple freely, but previously to 1848 had
most rarely conceived. In the Reports published since this date three
species have produced young (hybrids in one case), and, wonderful to
relate, the white Polar bear has produced young. The badger (Meles
taxus) has bred several times in the Gardens; but I have not heard of
this occurring elsewhere in England, and the event must be very rare,
for an instance in Germany has been thought worth recording.[340] In

Paraguay the native Nasua, though kept in pairs during many years and
perfectly tamed, has never been known, according to Rengger, to breed
or show any sexual passion; nor, as I hear from Mr. Bates, does this
animal, or the Cercoleptes, breed in the region of the Amazons. Two
other plantigrade genera, Procyon and Gulo, though often kept tame in
Paraguay, never breed there. In the Zoological Gardens species of
Nasua and Procyon have been seen to couple; but they did not produce
young.
As domesticated rabbits, guinea-pigs, and white mice breed so
abundantly when closely confined under various climates, it might
have been thought that most other members of the Rodent order would
have bred in captivity, but this is not the case. It deserves notice, as
showing how the capacity to breed sometimes goes by affinity, that the
one native rodent of Paraguay, which there breeds freely and has
yielded successive generations, is the Cavia aperea; and this animal is
so closely allied to the guinea-pig, that it has been erroneously thought
to be the parent-form.[341] In the Zoological Gardens, some rodents
have coupled, but have never produced young; some have neither
coupled nor bred; but a few have bred, as the porcupine more than
once, the Barbary mouse, lemming, chinchilla, and the agouti
(Dasyprocta aguti), several times. This latter animal has also produced
young in Paraguay, though they were born dead and ill-formed; but in
Amazonia, according to Mr. Bates, it never breeds, though often kept
tame about the houses. Nor does the paca (Cœlogenys paca) breed
there. The common hare when confined has, I believe, never bred in
Europe;[342] though, according to a recent statement, it has crossed
with the rabbit. I have never heard of the dormouse breeding in
confinement. But squirrels offer a more curious case: with one
exception, no species has ever bred in the Zoological Gardens, yet as
many as fourteen individuals of S. palmarum were kept together during
several years. The S. cinerea has been seen to couple, but it did not
produce young; nor has this species, when rendered extremely tame in
its native country, North America, been ever known to breed.[343] At
Lord Derby's menagerie squirrels of many kinds were kept in numbers,
but Mr. Thompson, the superintendent, told me that none had ever bred
there, or elsewhere as far as he knew. I have never heard of the English

squirrel breeding in confinement. But the species which has bred more
than once in the Zoological Gardens is the one which perhaps might
have been least expected, namely, the flying squirrel (Sciuropterus
volucella): it has, also, bred several times near Birmingham; but the
female never produced more than two young at a birth, whereas in its
native American home she bears from three to six young.[344]
Monkeys, in the nine-year Report from the Zoological Gardens, are
stated to unite most freely, but during this period, though many
individuals were kept, there were only seven births. I have heard of
one American monkey alone, the Ouistiti, breeding in Europe.[345] A
Macacus, according to Flourens, bred in Paris; and more than one
species of this genus has produced young in London, especially the
Macacus rhesus, which everywhere shows a special capacity to breed
under confinement. Hybrids have been produced both in Paris and
London from this same genus. The Arabian baboon, or Cynocephalus
hamadryas,[346] and a Cercopithecus have bred in the Zoological
Gardens, and the latter species at the Duke of Northumberland's.
Several members of the family of Lemurs have produced hybrids in the
Zoological Gardens. It is much more remarkable that monkeys very
rarely breed when confined in their native country; thus the Cay
(Cebus azaræ) is frequently and completely tamed in Paraguay, but
Rengger[347] says that it breeds so rarely, that he never saw more than
two females which had produced young. A similar observation has
been made with respect to the monkeys which are frequently tamed by
the aborigines in Brazil.[348] In the region of the Amazons, these
animals are so often kept in a tame state, that Mr. Bates in walking
through the streets of Parà counted thirteen species; but, as he asserts,
they have never been known to breed in captivity.[349]

Birds.

Birds offer in some respects better evidence than quadrupeds, from
their breeding more rapidly and being kept in greater numbers. We
have seen that carnivorous animals are more fertile under confinement
than most other mammals. The reverse holds good with carnivorous
birds. It is said[350] that as many as eighteen species have been used in
Europe for hawking, and several others in Persia and India;[351] they
have been kept in their native country in the finest condition, and have
been flown during six, eight, or nine years;[352] yet there is no record
of their having ever produced young. As these birds were formerly
caught whilst young, at great expense, being imported from Iceland,
Norway, and Sweden, there can be little doubt that, if possible, they
would have been propagated. In the Jardin des Plantes, no bird of prey
has been known to couple.[353] No hawk, vulture, or owl has ever
produced fertile eggs in the Zoological Gardens, or in the old Surrey
Gardens, with the exception, in the former place on one occasion, of a
condor and a kite (Milvus niger). Yet several species, namely, the
Aquila fusca, Haliætus leucocephalus, Falco tinnunculus, F. subbuteo,
and Buteo vulgaris, have been seen to couple in the Zoological
Gardens. Mr. Morris[354] mentions as a unique fact that a kestrel (Falco
tinnunculus) bred in an aviary. The one kind of owl which has been
known to couple in the Zoological Gardens was the Eagle Owl (Bubo
maximus); and this species shows a special inclination to breed in
captivity; for a pair at Arundel Castle, kept more nearly in a state of
nature "than ever fell to the lot of an animal deprived of its liberty,"
[355] actually reared their young. Mr. Gurney has given another

instance of this same owl breeding in confinement; and he records the
case of a second species of owl, the Strix passerina, breeding in
captivity.[356]
Of the smaller graminivorous birds, many kinds have been kept tame
in their native countries, and have lived long; yet, as the highest
authority on cage-birds[357] remarks, their propagation is
"uncommonly difficult." The canary-bird shows that there is no
inherent difficulty in these birds breeding freely in confinement; and

Audubon says[358] that the Fringilla (Spiza) ciris of North America
breeds as perfectly as the canary. The difficulty with the many finches
which have been kept in confinement is all the more remarkable as
more than a dozen species could be named which have yielded hybrids
with the canary; but hardly any of these, with the exception of the
siskin (Fringilla spinus), have reproduced their own kind. Even the
bullfinch (Loxia pyrrhula) has bred as frequently with the canary,
though belonging to a distinct genus, as with its own species.[359] With
respect to the skylark (Alauda arvensis), I have heard of birds living
for seven years in an aviary, which never produced young; and a great
London bird-fancier assured me that he had never known an instance
of their breeding; nevertheless one case has been recorded.[360] In the
nine-year Report from the Zoological Society, twenty-four incessorial
species are enumerated which had not bred, and of these only four
were known to have coupled.
Parrots are singularly long-lived birds; and Humboldt mentions the
curious fact of a parrot in South America, which spoke the language of
an extinct Indian tribe, so that this bird preserved the sole relic of a lost
language. Even in this country there is reason to believe[361] that
parrots have lived to the age of nearly one hundred years; yet, though
many have been kept in Europe, they breed so rarely that the event has
been thought worth recording in the gravest publications.[362]
According to Bechstein[363] the African Psittacus erithacus breeds
oftener than any other species: the P. macoa occasionally lays fertile
eggs, but rarely succeeds in hatching them; this bird, however, has the
instinct of incubation sometimes so strongly developed, that it will
hatch the eggs of fowls or pigeons. In the Zoological Gardens and in
the old Surrey Gardens some few species have coupled, but, with the
exception of three species of parrakeets, none have bred. It is a much
more remarkable fact that in Guiana parrots of two kinds, as I am
informed by Sir E. Schomburgk, are often taken from the nests by the
Indians and reared in large numbers; they are so tame that they fly
freely about the houses, and come when called to be fed, like pigeons;
yet he has never heard of a single instance of their breeding.[364] In
Jamaica, a resident naturalist, Mr. R. Hill,[365] says, "no birds more

readily submit to human dependence than the parrot-tribe, but no
instance of a parrot breeding in this tame life has been known yet." Mr.
Hill specifies a number of other native birds kept tame in the West
Indies, which never breed in this state.
The great pigeon family offers a striking contrast with parrots: in the
nine-year Report thirteen species are recorded as having bred, and,
what is more noticeable, only two were seen to couple without any
result. Since the above date every annual Report gives many cases of
various pigeons breeding. The two magnificent crowned pigeons
(Goura coronata and Victoriæ) produced hybrids; nevertheless, of the
former species more than a dozen birds were kept, as I am informed by
Mr. Crawfurd, in a park at Penang, under a perfectly well-adapted
climate, but never once bred. The Columba migratoria in its native
country, North America, invariably lays two eggs, but in Lord Derby's
menagerie never more than one. The same fact has been observed with
the C. leucocephala.[366]
Gallinaceous birds of many genera likewise show an eminent capacity
for breeding under captivity. This is particularly the case with
pheasants; yet our English species seldom lays more than ten eggs in
confinement; whilst from eighteen to twenty is the usual number in the
wild state.[367] With the Gallinaceæ, as with all other orders, there are
marked and inexplicable exceptions in regard to the fertility of certain
species and genera under confinement. Although many trials have been
made with the common partridge, it has rarely bred, even when reared
in large aviaries; and the hen will never hatch her own eggs.[368] The
American tribe of Guans or Cracidæ are tamed with remarkable ease,
but are very shy breeders in this country;[369] but with care various
species were formerly made to breed rather freely in Holland.[370]
Birds of this tribe are often kept in a perfectly tamed condition in their
native country by the Indians, but they never breed.[371] It might have
been expected that grouse from their habits of life would not have bred
in captivity, more especially as they are said soon to languish and die.
[372] But many cases are recorded of their breeding: the capercailzie

(Tetrao urogallus) has bred in the Zoological Gardens; it breeds
without much difficulty when confined in Norway, and in Russia five

successive generations have been reared: Tetrao tetrix has likewise
bred in Norway; T. Scoticus in Ireland; T. umbellus at Lord Derby's;
and T. cupido in North America.
It is scarcely possible to imagine a greater change in habits than that
which the members of the ostrich family must suffer, when cooped up
in small enclosures under a temperate climate, after freely roaming
over desert and tropical plains or entangled forests. Yet almost all the
kinds, even the mooruk (Casuarius Bennettii) from New Ireland, has
frequently produced young in the various European menageries. The
African ostrich, though perfectly healthy and living long in the South
of France, never lays more than from twelve to fifteen eggs, though in
its native country it lays from twenty-five to thirty.[373] Here we have
another instance of fertility impaired, but not lost, under confinement,
as with the flying squirrel, the hen-pheasant, and two species of
American pigeons.
Most Waders can be tamed, as the Rev. E. S. Dixon informs me, with
remarkable facility; but several of them are short-lived under
confinement, so that their sterility in this state is not surprising. The
cranes breed more readily than other genera: Grus montigresia has
bred several times in Paris and in the Zoological Gardens, as has G.
cinerea at the latter place, and G. antigone at Calcutta. Of other
members of this great order, Tetrapteryx paradisea has bred at
Knowsley, a Porphyrio in Sicily, and the Gallinula chloropus in the
Zoological Gardens. On the other hand, several birds belonging to this
order will not breed in their native country, Jamaica; and the Psophia,
though often kept by the Indians of Guiana about their houses, "is
seldom or never known to breed."[374]
No birds breed with such complete facility under confinement as the
members of the great Duck family; yet, considering their aquatic and
wandering habits, and the nature of their food, this could not have been
anticipated. Even some time ago above two dozen species had bred in
the Zoological Gardens; and M. Selys-Longchamps has recorded the
production of hybrids from forty-four different members of the family;
and to these Professor Newton has added a few more cases.[375] "There
is not," says Mr. Dixon,[376] "in the wide world, a goose which is not in

the strict sense of the word domesticable;" that is, capable of breeding
under confinement; but this statement is probably too bold. The
capacity to breed sometimes varies in individuals of the same species;
thus Audubon[377] kept for more than eight years some wild geese
(Anser Canadensis), but they would not mate; whilst other individuals
of the same species produced young during the second year. I know of
but one instance in the whole family of a species which absolutely
refuses to breed in captivity, namely, the Dendrocygna viduata,
although, according to Sir R. Schomburgk,[378] it is easily tamed, and
is frequently kept by the Indians of Guiana. Lastly, with respect to
Gulls, though many have been kept in the Zoological Gardens and in
the old Surrey Gardens, no instance was known before the year 1848
of their coupling or breeding; but since that period the herring gull
(Larus argentatus) has bred many times in the Zoological Gardens and
at Knowsley.
There is reason to believe that insects are affected by confinement like
the higher animals. It is well known that the Sphingidæ rarely breed
when thus treated. An entomologist[379] in Paris kept twenty-five
specimens of Saturnia pyri, but did not succeed in getting a single
fertile egg. A number of females of Orthosia munda and of Mamestra
suasa reared in confinement were unattractive to the males.[380] Mr.
Newport kept nearly a hundred individuals of two species of Vanessa,
but not one paired; this, however, might have been due to their habit of
coupling on the wing.[381] Mr. Atkinson could never succeed in India
in making the Tarroo silk-moth breed in confinement.[382] It appears
that a number of moths, especially the Sphingidæ, when hatched in the
autumn out of their proper season, are completely barren; but this latter
case is still involved in some obscurity.[383]

Independently of the fact of many animals under confinement not coupling,
or, if they couple, not producing young, there is evidence of another kind,
that their sexual functions are thus disturbed. For many cases have been
recorded of the loss by male birds when confined of their characteristic
plumage. Thus the common linnet (Linota cannabina) when caged does not
acquire the fine crimson colour on its breast, and one of the buntings
(Emberiza passerina) loses the black on its head. A Pyrrhula and an Oriolus

have been observed to assume the quiet plumage of the hen-bird; and the
Falco albidus returned to the dress of an earlier age.[384] Mr. Thomson, the
superintendent of the Knowsley menagerie, informed me that he had often
observed analogous facts. The horns of a male deer (Cervus Canadensis)
during the voyage from America were badly developed; but subsequently in
Paris perfect horns were produced.
When conception takes place under confinement, the young are often born
dead, or die soon, or are ill-formed. This frequently occurs in the Zoological
Gardens, and, according to Rengger, with native animals confined in
Paraguay. The mother's milk often fails. We may also attribute to the
disturbance of the sexual functions the frequent occurrence of that
monstrous instinct which leads the mother to devour her own offspring,—a
mysterious case of perversion, as it at first appears.
Sufficient evidence has now been advanced to prove that animals when first
confined are eminently liable to suffer in their reproductive systems. We
feel at first naturally inclined to attribute the result to loss of health, or at
least to loss of vigour; but this view can hardly be admitted when we reflect
how healthy, long-lived, and vigorous many animals are under captivity,
such as parrots, and hawks when used for hawking, chetahs when used for
hunting, and elephants. The reproductive organs themselves are not
diseased; and the diseases, from which animals in menageries usually
perish, are not those which in any way affect their fertility. No domestic
animal is more subject too disease than the sheep, yet it is remarkably
prolific. The failure of animals to breed under confinement has been
sometimes attributed exclusively to a failure in their sexual instincts: this
may occasionally come into play, but there is no obvious reason why this
instinct should be especially liable to be affected with perfectly tamed
animals, except indeed indirectly through the reproductive system itself
being disturbed. Moreover, numerous cases have been given of various
animals which couple freely under confinement, but never conceive; or, if
they conceive and produce young, these are fewer in number than is natural
to the species. In the vegetable kingdom instinct of course can play no part;
and we shall presently see that plants when removed from their natural
conditions are affected in nearly the same manner as animals. Change of
climate cannot be the cause of the loss of fertility, for, whilst many animals
imported into Europe from extremely different climates breed freely, many

others when confined in their native land are completely sterile. Change of
food cannot be the chief cause; for ostriches, ducks, and many other
animals, which must have undergone a great change in this respect, breed
freely. Carnivorous birds when confined are extremely sterile; whilst most
carnivorous mammals, except plantigrades, are moderately fertile. Nor can
the amount of food be the cause; for a sufficient supply will certainly be
given to valuable animals; and there is no reason to suppose that much more
food would be given to them, than to our choice domestic productions
which retain their full fertility. Lastly, we may infer from the case of the
elephant, chetah, various hawks, and of many animals which are allowed to
lead an almost free life in their native land, that want of exercise is not the
sole cause.
It would appear that any change in the habits of life, whatever these habits
may be, if great enough, tends to affect in an inexplicable manner the
powers of reproduction. The result depends more on the constitution of the
species than on the nature of the change; for certain whole groups are
affected more than others; but exceptions always occur, for some species in
the most fertile groups refuse to breed, and some in the most sterile groups
breed freely. Those animals which usually breed freely under confinement,
rarely breed, as I was assured, in the Zoological Gardens, within a year or
two after their first importation. When an animal which is generally sterile
under confinement happens to breed, the young apparently do not inherit
this power; for had this been the case, various quadrupeds and birds, which
are valuable for exhibition, would have become common. Dr. Broca even
affirms[385] that many animals in the Jardin des Plantes, after having
produced young for three or four successive generations, become sterile;
but this may be the result of too close interbreeding. It is a remarkable
circumstance that many mammals and birds have produced hybrids under
confinement quite as readily as, or even more readily than, they have
procreated their own kind. Of this fact many instances have been given;[386]
and we are thus reminded of those plants which when cultivated refuse to
be fertilised by their own pollen, but can easily be fertilised by that of a
distinct species. Finally, we must conclude, limited as the conclusion is, that
changed conditions of life have an especial power of acting injuriously on
the reproductive system. The whole case is quite peculiar, for these organs,

though not diseased, are thus rendered incapable of performing their proper
functions, or perform them imperfectly.

Sterility of Domesticated Animals from changed conditions.—With
respect to domesticated animals, as their domestication mainly depends
on the accident of their breeding freely under captivity, we ought not to
expect that their reproductive system would be affected by any
moderate degree of change. Those orders of quadrupeds and birds, of
which the wild species breed most readily in our menageries, have
afforded us the greatest number of domesticated productions. Savages
in most parts of the world are fond of taming animals;[387] and if any of
these regularly produced young, and were at the same time useful, they
would be at once domesticated. If, when their masters migrated into
other countries, they were in addition found capable of withstanding
various climates, they would be still more valuable; and it appears that
the animals which breed readily in captivity can generally withstand
different climates. Some few domesticated animals, such as the
reindeer and camel, offer an exception to this rule. Many of our
domesticated animals can bear with undiminished fertility the most
unnatural conditions; for instance, rabbits, guinea-pigs, and ferrets
breed in miserably confined hutches. Few European dogs of any kind
withstand without degeneration the climate of India; but as long as
they survive, they retain, as I hear from Mr. Falconer, their fertility; so
it is, according to Dr. Daniell, with English dogs taken to Sierra Leone.
The fowl, a native of the hot jungles of India, becomes more fertile
than its parent-stock in every quarter of the world, until we advance as
far north as Greenland and Northern Siberia, where this bird will not
breed. Both fowls and pigeons, which I received during the autumn
direct from Sierra Leone, were at once ready to couple.[388] I have,
also, seen pigeons breeding as freely as the common kinds within a
year after their importation from the Upper Nile. The guinea-fowl, an
aboriginal of the hot and dry deserts of Africa, whilst living under our
damp and cool climate, produces a large supply of eggs.
Nevertheless, our domesticated animals under new conditions
occasionally show signs of lessened fertility. Roulin asserts that in the
hot valleys of the equatorial Cordillera sheep are not fully fecund;[389]

and according to Lord Somerville,[390] the merino-sheep which he
imported from Spain were not at first perfectly fertile. It is said[391]
that mares brought up on dry food in the stable, and turned out to
grass, do not at first breed. The peahen, as we have seen, is said not to
lay so many eggs in England as in India. It was long before the canary-
bird was fully fertile, and even now first-rate breeding birds are not
common.[392] In the hot and dry province of Delhi, the eggs of the
turkey, as I hear from Dr. Falconer, though placed under a hen, are
extremely liable to fail. According to Roulin, geese taken within a
recent period to the lofty plateau of Bogota, at first laid seldom, and
then only a few eggs; of these scarcely a fourth were hatched, and half
the young birds died: in the second generation they were more fertile;
and when Roulin wrote they were becoming as fertile as our geese in
Europe. In the Philippine Archipelago the goose, it is asserted, will not
breed or even lay eggs.[393] A more curious case is that of the fowl,
which, according to Roulin, when first introduced would not breed at
Cusco in Bolivia, but subsequently became quite fertile; and the
English Game fowl, lately introduced, had not as yet arrived a its full
fertility, for to raise two or three chickens from a nest of eggs was
thought fortunate. In Europe close confinement has a marked effect on
the fertility of the fowl: it has been found in France that with fowls
allowed considerable freedom only twenty per cent. of the eggs failed;
when allowed less freedom forty per cent. failed; and in close
confinement sixty out of the hundred were not hatched.[394] So we see
that unnatural and changed conditions of life produce some effect on
the fertility of our most thoroughly domesticated animals, in the same
manner, though in a far less degree, as with captive wild animals.
It is by no means rare to find certain males and females which will not
breed together, though both are known to be perfectly fertile with other
males and females. We have no reason to suppose that this is caused by
these animals having been subjected to any change in their habits of
life; therefore such cases are hardly related to our present subject. The
cause apparently lies in an innate sexual incompatibility of the pair
which are matched. Several instances have been communicated to me
by Mr. W. C. Spooner (well known for his essay on Cross-breeding),
by Mr. Eyton of Eyton, by Mr. Wicksted and othe breeders, and

especially by Mr. Waring of Chelsfield, in relation to horses, cattle,
pigs, foxhounds, other dogs, and pigeons.[395] In these cases, females,
which either previously or subsequently were proved to be fertile,
failed to breed with certain males, with whom it was particularly
desired to match them. A change in the constitution of the female may
sometimes have occurred before she was put to the second male; but in
other cases this explanation is hardly tenable, for a female, known not
to be barren, has been unsuccessfully paired seven or eight times with
the same male likewise known to be perfectly fertile. With cart-mares,
which sometimes will not breed with stallions of pure blood, but
subsequently have bred with cart-stallions, Mr. Spooner is inclined to
attribute the failure to the lesser sexual power of the race-horse. But I
have heard from the greatest breeder of race-horses at the present day,
through Mr. Waring, that "it frequently occurs with a mare to be put
several times during one or two seasons to a particular stallion of
acknowledged power, and yet prove barren; the mare afterwards
breeding at once with some other horse." These facts are worth
recording, as they show, like so many previous facts, on what slight
constitutional differences the fertility of an animal often depends.

Sterility of Plants from changed Conditions of Life, and from other causes.
In the vegetable kingdom cases of sterility frequently occur, analogous with
those previously given in the animal kingdom. But the subject is obscured
by several circumstances, presently to be discussed, namely, the
contabescence of the anthers, as Gärtner has named a certain affection—
monstrosities—doubleness of the flower—much-enlarged fruit—and long-
continued or excessive propagation by buds.

It is notorious that many plants in our gardens and hot-houses, though
preserved in the most perfect health, rarely or never produce seed. I do
not allude to plants which run to leaves, from being kept too damp, or
too warm, or too much manured; for these do not produce the
reproductive individual or flower, and the case may be wholly
different. Nor do I allude to fruit not ripening from want of heat, or
rotting from too much moisture. But many exotic plants, with their
ovules and pollen appearing perfectly sound, will not set any seed. The
sterility in many cases, as I know from my own observation, is simply

due to the absence of the proper insects for carrying the pollen to the
stigma. But after excluding the several cases just specified, there are
many plants in which the reproductive system has been seriously
affected by the altered conditions of life to which they have been
subjected.
It would be tedious to enter on many details. Linnæus long ago
observed[396] that Alpine plants, although naturally laded with seed,
produce either few or none when cultivated in gardens. But exceptions
often occur: the Draba sylvestris, one of our most thoroughly Alpine
plants, multiplies itself by seed in Mr. H. C. Watson's garden, near
London; and Kerner, who has particularly attended to the cultivation of
Alpine plants, found that various kinds, when cultivated,
spontaneously sowed themselves.[397] Many plants which naturally
grow in peat-earth are entirely sterile in our gardens. I have noticed the
same fact with several liliaceous plants, which nevertheless grew
vigorously.
Too much manure renders some kinds utterly sterile, as I have myself
observed. The tendency to sterility from this cause runs in families;
thus, according to Gärtner,[398] it is hardly possible to give too much
manure to most Gramineæ, Cruciferæ, and Leguminosæ, whilst
succulent and bulbous-rooted plants are easily affected. Extreme
poverty of soil is less apt to induce sterility; but dwarfed plants of
Trifolium minus and repens, growing on a lawn often mown and never
manured, did not produce any seed. The temperature of the soil, and
the season at which plants are watered, often have a marked effect on
their fertility, as was observed by Kölreuter in the case of Mirabilis.
[399] Mr. Scott in the Botanic Gardens of Edinburgh observed that

Oncidium divaricatum would not set seed when grown in a basket in
which it throve, but was capable of fertilisation in a pot where it was a
little damper. Pelargonium fulgidum, for many years after its
introduction, seeded freely; it then became sterile; now it is fertile[400]
if kept in a dry stove during the winter. Other varieties of pelargonium
are sterile and others fertile without our being able to assign any cause.
Very slight changes in the position of a plant, whether planted on a
bank or at its base, sometimes make all the difference in its producing

seed. Temperature apparently has a much more powerful influence on
the fertility of plants than on that of animals. Nevertheless it is
wonderful what changes some few plants will withstand with
undiminished fertility: thus the Zephyranthes candida, a native of the
moderately warm banks of the Plata, sows itself in the hot dry country
near Lima, and in Yorkshire resists the severest frosts, and I have seen
seeds gathered from pods which had been covered with snow during
three weeks.[401] Berberis Wallichii, from the hot Khasia range in
India, is uninjured by our sharpest frosts, and ripens its fruit under our
cool summers. Nevertheless I presume we must attribute to change of
climate the sterility of many foreign plants; thus the Persian and
Chinese lilacs (Syringa Persica and Chinensis), though perfectly
hardly, never here produce a seed; the common lilac (S. vulgaris) seeds
with us moderately well, but in parts of Germany the capsules never
contain seed.[402]
Some of the cases, given in the last chapter, of self-impotent plants,
which are fertile both on the male and female side when united with
distinct individuals or species, might have been here introduced; for as
this peculiar form of sterility generally occurs with exotic plants or
with endemic plants cultivated in pots, and as it disappeared in the
Passiflora alata when grafted, we may conclude that in these cases it is
the result of the treatment to which the plants or their parents have
been exposed.
The liability of plants to be affected in their fertility by slightly
changed conditions is the more remarkable, as the pollen when once in
process of formation is not easily injured; a plant may be transplanted,
or a branch with flower-buds be cut off and placed in water, and the
pollen will be matured. Pollen, also, when once mature, may be kept
for weeks or even months.[403] The female organs are more sensitive,
for Gärtner[404] found that dicotyledonous plants, when carefully
removed so that they did not in the least flag, could seldom be
fertilised; this occurred even with potted plants if the roots had grown
out of the hole at the bottom. In some few cases, however, as with
Digitalis, transplantation did not prevent fertilisation; and according to
the testimony of Mawz, Brassica rapa, when pulled up by its roots and

placed in water, ripened its seed. Flower-stems of several
monocotyledonous plants when cut off and placed in water likewise
produce seed. But in these cases I presume that the flowers had been
already fertilised, for Herbert[405] found with the Crocus that the plants
might be removed or mutilated after the act of fertilisation, and would
still perfect their seeds; but that, if transplanted before being fertilised,
the application of pollen was powerless.
Plants which have been long cultivated can generally endure with
undiminished fertility various and great changes; but not in most cases
so great a change of climate as domesticated animals. It is remarkable
that many plants under these circumstances are so much affected that
the proportions and the nature of their chemical ingredients are
modified, yet their fertility is unimpaired. Thus, as Dr. Falconer
informs me, there is a great difference in the character of the fibre in
hemp, in the quantity of oil in the seed of the Linum, in the proportion
of narcotin to morphine in the poppy, in gluten to starch in wheat,
when these plants are cultivated on the plains and on the mountains of
India; nevertheless, they all remain fully fertile.
Contabescence.—Gärtner has designated by this term a peculiar
condition of the anthers in certain plants, in which they are shrivelled,
or become brown and tough, and contain no good pollen. When in this
state they exactly resemble the anthers of the most sterile hybrids.
Gärtner,[406] in his discussion on this subject, has shown that plants of
many orders are occasionally thus affected; but the Caryophyllaceæ
and Liliaceæ suffer most, and to these orders, I think, the Ericaceæ
may be added. Contabescence varies in degree, but on the same plant
all the flowers are generally affected to nearly the same extent. The
anthers are affected at a very early period in the flower-bud, and
remain in the same state (with one recorded exception) during the life
of the plant. The affection cannot be cured by any change of treatment,
and is propagated by layers, cuttings, &c., and perhaps even by seed.
In contabescent plants the female organs are seldom affected, or
merely become precocious in their development. The cause of this
affection is doubtful, and is different in different cases. Until I read
Gärtner's discussion I attributed it, as apparently did Herbert, to the
unnatural treatment of the plants; but its permanence under changed

conditions, and the female organs not being affected, seem
incompatible with this view. The fact of several endemic plants
becoming contabescent in our gardens seems, at first sight, equally
incompatible with this view; but Kölreuter believes that this is the
result of their transplantation. The contabescent plants of Dianthus and
Verbascum, found wild by Wiegmann, grew on a dry and sterile bank.
The fact that exotic plants are eminently liable to this affection also
seems to show that it is in some manner caused by their unnatural
treatment. In some instances, as with Silene, Gärtner's view seems the
most probable, namely, that it is caused by an inherent tendency in the
species to become diœcious. I can add another cause, namely, the
illegitimate unions of reciprocally dimorphic or trimorphic plants, for I
have observed seedlings of three species of Primula and of Lythrum
salicaria, which had been raised from plants illegitimately fertilised by
their own-form pollen, with some or all their anthers in a contabescent
state. There is perhaps an additional cause, namely, self-fertilisation;
for many plants of Dianthus and Lobelia, which had been raised from
self-fertilised seeds, had their anthers in this state; but these instances
are not conclusive, as both genera are liable from other causes to this
affection.
Cases of an opposite nature likewise occur, namely, plants with the
female organs struck with sterility, whilst the male organs remain
perfect. Dianthus Japonicus, a Passiflora, and Nicotiana, have been
described by Gärtner[407] as being in this unusual condition.
Monstrosities as a cause of Sterility.—Great deviations of structure,
even when the reproductive organs themselves are not seriously
affected, sometimes cause plants to become sterile. But in other cases
plants may become monstrous to an extreme degree and yet retain their
full fertility. Gallesio, who certainly had great experience,[408] often
attributes sterility to this cause; but it may be suspected that in some of
his cases sterility was the cause, and not the result, of the monstrous
growths. The curious St. Valery apple, although it bears fruit, rarely
produces seed. The wonderfully anomalous flowers of Begonia frigida,
formerly described, though they appear fit for fructification, are sterile.
[409] Species of Primulæ, in which the calyx is brightly coloured, are

said[410] to be often sterile, though I have known them to be fertile. On
the other hand, Verlot gives several cases of proliferous flowers which
can be propagated by seed. This was the case with a poppy, which had
become monopetalous by the union of its petals.[411] Another
extraordinary poppy, with the stamens replaced by numerous small
supplementary capsules, likewise reproduces itself by seed. This has
also occurred with a plant of Saxifraga geum, in which a series of
adventitious carpels, bearing ovules on their margins, had been
developed between the stamens and the normal carpels.[412] Lastly,
with respect to peloric flowers, which depart wonderfully from the
natural structure,—those of Linaria vulgaris seem generally to be more
or less sterile, whilst those before described of Antirrhinum majus,
when artificially fertilised with their own pollen, are perfectly fertile,
though sterile when left to themselves, for bees are unable to crawl into
the narrow tubular flower. The peloric flowers of Corydalis solida,
according to Godron,[413] are barren; whilst those of Gloxinia are well
known to yield plenty of seed. In our greenhouse Pelargoniums, the
central flower of the truss is often peloric, and Mr. Masters informs me
that he tried in vain during several years to get seed from these
flowers. I likewise made many vain attempts, but sometimes succeeded
in fertilising them with pollen from a normal flower of another variety;
and conversely I several times fertilised ordinary flowers with peloric
pollen. Only once I succeeded in raising a plant from a peloric flower
fertilised by pollen from a peloric flower borne by another variety; but
the plant, it may be added, presented nothing particular in its structure.
Hence we may conclude that no general rule can be laid down; but any
great deviation from the normal structure, even when the reproductive
organs themselves are not seriously affected, certainly often leads to
sexual impotence.
Double Flowers.—When the stamens are converted into petals, the
plant becomes on the male side sterile; when both stamens and pistils
are thus changed, the plant becomes completely barren. Symmetrical
flowers having numerous stamens and petals are the most liable to
become double, as perhaps follows from all multiple organs being the
most subject to variability. But flowers furnished with only a few
stamens, and others which are asymmetrical in structure, sometimes

become double, as we see with the double gorse or Ulex, Petunia, and
Antirrhinum. The Compositæ bear what are called double flowers by
the abnormal development of the corolla of their central florets.
Doubleness is sometimes connected with prolification,[414] or the
continued growth of the axis of the flower. Doubleness is strongly
inherited. No one has produced, as Lindley remarks,[415] double
flowers by promoting the perfect health of the plant. On the contrary,
unnatural conditions of life favour their production. There is some
reason to believe that seeds kept during many years, and seeds
believed to be imperfectly fertilised, yield double flowers more freely
than fresh and perfectly fertilised seed.[416] Long-continued cultivation
in rich soil seems to be the commonest exciting cause. A double
narcissus and a double Anthemis nobilis, transplanted into very poor
soil, have been observed to become single;[417] and I have seen a
completely double white primrose rendered permanently single by
being divided and transplanted whilst in full flower. It has been
observed by Professor Morren that doubleness of the flowers and
variegation of the leaves are antagonistic states; but so many
exceptions to the rule have lately been recorded,[418] that, though
general, it cannot be looked at as invariable. Variegation seems
generally to result from a feeble or atrophied condition of the plant,
and a large proportion of the seedlings raised from parents both of
which are variegated usually perish at an early age; hence we may
perhaps infer that doubleness, which is the antagonistic state,
commonly arises from a plethoric condition. On the other hand,
extremely poor soil sometimes, though rarely, appears to cause
doubleness: I formerly described[419] some completely double, bud-
like, flowers produced in large numbers by stunted wild plants of
Gentiana amarella growing on a poor chalky bank. I have also noticed
a distinct tendency to doubleness in the flowers of a Ranunculus,
Horse-chesnut, and Bladder-nut (Ranunculus repens, Æsculus pavia,
and Staphylea), growing under very unfavourable conditions. Professor
Lehman[420] found several wild plants growing near a hot spring with
double flowers. With respect to the cause of doubleness, which arises,
as we see, under widely different circumstances, I shall presently
attempt to show that the most probable view is that unnatural

conditions first give a tendency to sterility, and that then, on the
principle of compensation, as the reproductive organs do not perform
their proper functions, they either become developed into petals, or
additional petals are formed. This view has lately been supported by
Mr. Laxton,[421] who advances the case of some common peas, which,
after long-continued heavy rain, flowered a second time, and produced
double flowers.
Seedless Fruit.—Many of our most valuable fruits, although consisting
in a homological sense of widely different organs, are either quite
sterile, or produce extremely few seeds. This is notoriously the case
with our best pears, grapes, and figs, with the pine-apple, banana,
bread-fruit, pomegranate, azarole, date-palms, and some members of
the orange-tribe. Poorer varieties of these same fruits either habitually
or occasionally yield seed.[422] Most horticulturists look at the great
size and anomalous development of the fruit as the cause, and sterility
as the result; but the opposite view, as we shall presently see, is more
probable.
Sterility from the excessive development of the Organs of Growth or
Vegetation.—Plants which from any cause grow too luxuriantly, and
produce leaves, stems, runners, suckers, tubers, bulbs, &c., in excess,
sometimes do not flower, or if they flower do not yield seed. To make
European vegetables under the hot climate of India yield seed, it is
necessary to check their growth; and, when one-third grown, they are
taken up, and their stems and tap-roots are cut or mutilated.[423] So it is
with hybrids; for instance, Prof. Lecoq[424] had three plants of
Mirabilis, which, though they grew luxuriantly and flowered, were
quite sterile; but after beating one with a stick until a few branches
alone were left, these at once yielded good seed. The sugar-cane,
which grows vigorously and produces a large supply of succulent
stems, never, according to various observers, bears seed in the West
Indies, Malaga, India, Cochin China, or the Malay Archipelago.[425]
Plants which produce a large number of tubers are apt to be sterile, as
occurs, to a certain extent, with the common potato; and Mr. Fortune
informs me that the sweet potato (Convolvulus batatas) in China never,
as far as he has seen, yields seed. Dr. Royle remarks[426] that in India

the Agave vivipara, when grown in rich soil, invariably produces
bulbs, but no seeds; whilst a poor soil and dry climate leads to an
opposite result. In China, according to Mr. Fortune, an extraordinary
number of little bulbs are developed in the axils of the leaves of the
yam, and this plant does not bear seed. Whether in these cases, as in
those of double flowers and seedless fruit, sexual sterility from
changed conditions of life is the primary cause which leads to the
excessive development of the organs of vegetation, is doubtful; though
some evidence might be advanced in favour of this view. It is perhaps
a more probable view that plants which propagate themselves largely
by one method, namely by buds, have not sufficient vital power or
organised matter for the other method of sexual generation.
Several distinguished botanists and good practical judges believe that
long-continued propagation by cuttings, runners, tubers, bulbs, &c.,
independently of any excessive development of these parts, is the
cause of many plants failing to produce flowers and of others failing to
produce fertile flowers,—it is as if they had lost the habit of sexual
generation.[427] That many plants when thus propagated are sterile
there can be no doubt, but whether the long continuance of this form of
propagation is the actual cause of their sterility, I will not venture, from
the want of sufficient evidence, to express an opinion.
That plants may be propagated for long periods by buds, without the
aid of sexual generation, we may safely infer from this being the case
with many plants which must have long survived in a state of nature.
As I have had occasion before to allude to this subject, I will here give
such cases as I have collected. Many alpine plants ascend mountains
beyond the height at which they can produce seed.[428] Certain species
of Poa and Festuca, when growing on mountain-pastures, propagate
themselves, as I hear from Mr. Bentham, almost exclusively by
bulblets. Kalm gives a more curious instance[429] of several American
trees, which grow so plentifully in marshes or in thick woods, that they
are certainly well adapted for these stations, yet scarcely ever produce
seeds; but when accidentally growing on the outside of the marsh or
wood, are loaded with seed. The common ivy is found in Northern
Sweden and Russia, but flowers and fruits only in the southern

provinces. The Acorus calamus extends over a large portion of the
globe, but so rarely perfects its fruit that this has been seen but by few
botanists.[430] The Hypericum calycinum, which propagates itself so
freely in our shrubberies by rhizomas and is naturalised in Ireland,
blossoms profusely, but sets no seed; nor did it set any when fertilised
in my garden by pollen from plants growing at a distance. The
Lysimachia nummularia, which is furnished with long runners, so
seldom produces seed-capsules, that Prof. Decaisne,[431] who has
especially attended to this plant, has never seen it in fruit. The Carex
rigida often fails to perfect its seed in Scotland, Lapland, Greenland,
Germany, and New Hampshire in the United States.[432] The
periwinkle (Vinca minor), which spreads largely by runners, is said
scarcely ever to produce fruit in England;[433] but this plant requires
insect-aid for its fertilisation, and the proper insects may be absent or
rare. The Jussiæa grandiflora has become naturalised in Southern
France, and has spread by its rhizomas so extensively as to impede the
navigation of the waters, but never produces fertile seed.[434] The
horse-radish (Cochlearia armoracia) spreads pertinaciously and is
naturalised in various parts of Europe; though it bears flowers, these
rarely produce capsules: Professor Caspary also informs me that he has
watched this plant since 1851, but has never seen its fruit; nor is this
surprising, as he finds scarcely a grain of good pollen. The common
little Ranunculus ficaria rarely, and some say never, bears seed in
England, France, or Switzerland; but in 1863 I observed seeds on
several plants growing near my house. According to M. Chatin, there
are two forms of this Ranunculus; and it is the bulbiferous form which
does not yield seed from producing no pollen.[435] Other cases
analogous with the foregoing could be given; for instance, some kinds
of mosses and lichens have never been seen to fructify in France.
Some of these endemic and naturalised plants are probably rendered
sterile from excessive multiplication by buds, and their consequent
incapacity to produce and nourish seed. But the sterility of others more
probably depends on the peculiar conditions under which they live, as
in the case of the ivy in the northern parts of Europe, and of the trees in
the swamps of the United States; yet these plants must be in some

respects eminently well adapted for the stations which they occupy, for
they hold their places against a host of competitors.

Finally, when we reflect on the sterility which accompanies the doubling of
flowers,—the excessive development of fruit,—and a great increase in the
organs of vegetation, we must bear in mind that the whole effect has seldom
been caused at once. An incipient tendency is observed, and continued
selection completes the work, as is known to be the case with our double
flowers and best fruits. The view which seems the most probable, and
which connects together all the foregoing facts and brings them within our
present subject, is, that changed and unnatural conditions of life first give a
tendency to sterility; and in consequence of this, the organs of reproduction
being no longer able fully to perform their proper functions, a supply of
organised matter, not required for the development of the seed, flows either
into these same organs and renders them foliaceous, or into the fruit, stems,
tubers, &c., increasing their size and succulency. But I am far from wishing
to deny that there exists, independently of any incipient sterility, an
antagonism between the two forms of reproduction, namely, by seed and by
buds, when either is carried to an extreme degree. That incipient sterility
plays an important part in the doubling of flowers, and in the other cases
just specified, I infer chiefly from the following facts. When fertility is lost
from a wholly different cause, namely, from hybridism, there is a strong
tendency, as Gärtner[436] affirms, for flowers to become double, and this
tendency is inherited. Moreover it is notorious that with hybrids the male
organs become sterile before the female organs, and with double flowers the
stamens first become foliaceous. This latter fact is well shown by the male
flowers of diœcious plants, which, according to Gallesio,[437] first become
double. Again, Gärtner[438] often insists that the flowers of even utterly
sterile hybrids, which do not produce any seed, generally yield perfect
capsules or fruit,—a fact which has likewise been repeatedly observed by
Naudin with the Cucurbitaceæ; so that the production of fruit by plants
rendered sterile through any other and distinct cause is intelligible.
Kölreuter has also expressed his unbounded astonishment at the size and
development of the tubers in certain hybrids; and all experimentalists[439]
have remarked on the strong tendency in hybrids to increase by roots,
runners, and suckers. Seeing that hybrid plants, which from their nature are
more or less sterile, thus tend to produce double flowers; that they have the

parts including the seed, that is the fruit, perfectly developed, even when
containing no seed; that they sometimes yield gigantic roots; that they
almost invariably tend to increase largely by suckers and other such means;
—seeing this, and knowing, from the many facts given in the earlier parts of
this chapter, that almost all organic beings when exposed to unnatural
conditions tend to become more or less sterile, it seems much the most
probable view that with cultivated plants sterility is the exciting cause, and
double flowers, rich seedless fruit, and in some cases largely-developed
organs of vegetation, &c., are the indirect results—these results having been
in most cases largely increased through continued selection by man.

CHAPTER XIX.

SUMMARY OF THE FOUR LAST CHAPTERS, WITH REMARKS ON
HYBRIDISM.

ON THE EFFECTS OF CROSSING—THE INFLUENCE OF DOMESTICATION ON
FERTILITY—CLOSE INTERBREEDING—GOOD AND EVIL RESULTS FROM
CHANGED CONDITIONS OF LIFE—VARIETIES WHEN CROSSED NOT INVARIABLY
FERTILE—ON THE DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND
VARIETIES—CONCLUSIONS WITH RESPECT TO HYBRIDISM—LIGHT THROWN
ON HYBRIDISM BY THE ILLEGITIMATE PROGENY OF DIMORPHIC AND
TRIMORPHIC PLANTS—STERILITY OF CROSSED SPECIES DUE TO DIFFERENCES
CONFINED TO THE REPRODUCTIVE SYSTEM—NOT ACCUMULATED THROUGH
NATURAL SELECTION—REASONS WHY DOMESTIC VARIETIES ARE NOT
MUTUALLY STERILE—TOO MUCH STRESS HAS BEEN LAID ON THE DIFFERENCE
IN FERTILITY BETWEEN CROSSED SPECIES AND CROSSED VARIETIES—
CONCLUSION.

It was shown in the fifteenth chapter that when individuals of the same
variety, or even of a distinct variety, are allowed freely to intercross,
uniformity of character is ultimately acquired. Some few characters,
however, are incapable of fusion, but these are unimportant, as they are
almost always of a semi-monstrous nature, and have suddenly appeared.
Hence, to preserve our domesticated breeds true, or to improve them by
methodical selection, it is obviously necessary that they should be kept

separate. Nevertheless, through unconscious selection, a whole body of
individuals may be slowly modified, as we shall see in a future chapter,
without separating them into distinct lots. Domestic races have often been
intentionally modified by one or two crosses, made with some allied race,
and occasionally even by repeated crosses with very distinct races; but in
almost all such cases, long-continued and careful selection has been
absolutely necessary, owing to the excessive variability of the crossed
offspring, due to the principle of reversion. In a few instances, however,
mongrels have retained a uniform character from their first production.
When two varieties are allowed to cross freely, and one is much more
numerous than the other, the former will ultimately absorb the latter. Should
both varieties exist in nearly equal numbers, it is probable that a
considerable period would elapse before the acquirement of a uniform
character; and the character ultimately acquired would largely depend on
prepotency of transmission, and on the conditions of life; for the nature of
these conditions would generally favour one variety more than another, so
that a kind of natural selection would come into play. Unless the crossed
offspring were slaughtered by man without the least discrimination, some
degree of unmethodical selection would likewise come into action. From
these several considerations we may infer, that when two or more closely
allied species first came into the possession of the same tribe, their crossing
will not have influenced, in so great a degree as has often been supposed,
the character of the offspring in future times; although in some cases it
probably has had a considerable effect.
Domestication, as a general rule, increases the prolificness of animals and
plants. It eliminates the tendency to sterility which is common to species
when first taken from a state of nature and crossed. On this latter head we
have no direct evidence; but as our races of dogs, cattle, pigs, &c., are
almost certainly descended from aboriginally distinct stocks, and as these
races are now fully fertile together, or at least incomparably more fertile
than most species when crossed, we may with much confidence accept this
conclusion.
Abundant evidence has been given that crossing adds to the size, vigour,
and fertility of the offspring. This holds good when there has been no
previous close interbreeding. It applies to the individuals of the same

variety but belonging to different families, to distinct varieties, sub-species,
and partially even to species. In the latter case, though size is often gained,
fertility is lost; but the increased size, vigour, and hardiness of many
hybrids cannot be accounted for solely on the principle of compensation
from the inaction of the reproductive system. Certain plants, both of pure
and hybrid origin, though perfectly healthy, have become self-impotent,
apparently from the unnatural conditions to which they have been exposed;
and such plants, as well as others in their normal state, can be stimulated to
fertility only by crossing them with other individuals of the same species or
even of a distinct species.
On the other hand, long-continued close interbreeding between the nearest
relations diminishes the constitutional vigour, size, and fertility of the
offspring; and occasionally leads to malformations, but not necessarily to
general deterioration of form or structure. This failure of fertility shows that
the evil results of interbreeding are independent of the augmentation of
morbid tendencies common to both parents, though this augmentation no
doubt is often highly injurious. Our belief that evil follows from close
interbreeding rests to a large extent on the experience of practical breeders,
especially of those who have reared many animals of the kinds which can
be propagated quickly; but it likewise rests on several carefully recorded
experiments. With some animals close interbreeding may be carried on for a
long period with impunity by the selection of the most vigorous and healthy
individuals; but sooner or later evil follows. The evil, however, comes on so
slowly and gradually that it easily escapes observation, but can be
recognised by the almost instantaneous manner in which size, constitutional
vigour, and fertility are regained when animals that have long been
interbred are crossed with a distinct family.
These two great classes of facts, namely, the good derived from crossing,
and the evil from close interbreeding, with the consideration of the
innumerable adaptations throughout nature for compelling, or favouring, or
at least permitting, the occasional union of distinct individuals, taken
together, lead to the conclusion that it is a law of nature that organic beings
shall not fertilise themselves for perpetuity. This law was first plainly hinted
at in 1799, with respect to plants, by Andrew Knight,[440] and, not long
afterwards, that sagacious observer Kölreuter, after showing how well the
Malvaceæ are adapted for crossing, asks, "an id aliquid in recessu habeat,

quod hujuscemodi flores nunquam proprio suo pulvere, sed semper eo
aliarum suæ speciei impregnentur, merito quæritur? Certe natura nil facit
frustra." Although we may demur to Kölreuter's saying that nature does
nothing in vain, seeing how many organic beings retain rudimentary and
useless organs, yet undoubtedly the argument from the innumerable
contrivances, which favour the crossing of distinct individuals of the same
species, is of the greatest weight. The most important result of this law is
that it leads to uniformity of character in the individuals of the same
species. In the case of certain hermaphrodites, which probably intercross
only at long intervals of time, and with unisexual animals inhabiting
somewhat separated localities, which can only occasionally come into
contact and pair, the greater vigour and fertility of the crossed offspring will
ultimately prevail in giving uniformity of character to the individuals of the
same species. But when we go beyond the limits of the same species, free
intercrossing is barred by the law of sterility.
In searching for facts which might throw light on the cause of the good
effects from crossing, and of the evil effects from close interbreeding, we
have seen that, on the one hand, it is a widely prevalent and ancient belief
that animals and plants profit from slight changes in their condition of life;
and it would appear that the germ, in a somewhat analogous manner, is
more effectually stimulated by the male element, when taken from a distinct
individual, and therefore slightly modified in nature, than when taken from
a male having the same identical constitution. On the other hand, numerous
facts have been given, showing that when animals are first subjected to
captivity, even in their native land, and although allowed much liberty, their
reproductive functions are often greatly impaired or quite annulled. Some
groups of animals are more affected than others, but with apparently
capricious exceptions in every group. Some animals never or rarely couple:
some couple freely, but never or rarely conceive. The secondary male
characters, the maternal functions and instincts, are occasionally affected.
With plants, when first subjected to cultivation, analogous facts have been
observed. We probably owe our double flowers, rich seedless fruits, and in
some cases greatly developed tubers, &c., to incipient sterility of the above
nature combined with a copious supply of nutriment. Animals which have
long been domesticated, and plants which have long been cultivated, can
generally withstand with unimpaired fertility great changes in their

conditions of life; though both are sometimes slightly affected. With
animals the somewhat rare capacity of breeding freely under confinement
has mainly determined, together with their utility, the kinds which have
been domesticated.
We can in no case precisely say what is the cause of the diminished fertility
of an animal when first captured, or of a plant when first cultivated; we can
only infer that it is caused by a change of some kind in the natural
conditions of life. The remarkable susceptibility of the reproductive system
to such changes,—a susceptibility not common to any other organ,—
apparently has an important bearing on Variability, as we shall see in a
future chapter.
It is impossible not to be struck with the double parallelism between the two
classes of facts just alluded to. On the one hand, slight changes in the
conditions of life, and crosses between slightly modified forms or varieties,
are beneficial as far as prolificness and constitutional vigour are concerned.
On the other hand, changes in the conditions greater in degree, or of a
different nature, and crosses between forms which have been slowly and
greatly modified by natural means,—in other words, between species,—are
highly injurious, as far as the reproductive system is concerned, and in
some few instances as far as constitutional vigour is concerned. Can this
parallelism be accidental? Does it not rather indicate some real bond of
connection? As a fire goes out unless it be stirred up, so the vital forces are
always tending, according to Mr. Herbert Spencer, to a state of equilibrium,
unless disturbed and renovated through the action of other forces.
In some few cases varieties tend to keep distinct, by breeding at different
periods, by great differences in size, or by sexual preference,—in this latter
respect more especially resembling species in a state of nature. But the
actual crossing of varieties, far from diminishing, generally adds to the
fertility of both the first union and the mongrel offspring. Whether all the
most widely distinct domestic varieties are invariably quite fertile when
crossed, we do not positively know; much time and trouble would be
requisite for the necessary experiments, and many difficulties occur, such as
the descent of the various races from aboriginally distinct species, and the
doubts whether certain forms ought to be ranked as species or varieties.
Nevertheless, the wide experience of practical breeders proves that the great

majority of varieties, even if some should hereafter prove not to be
indefinitely fertile inter se, are far more fertile when crossed, than the vast
majority of closely allied natural species. A few remarkable cases have,
however, been given on the authority of excellent observers, showing that
with plants certain forms, which undoubtedly must be ranked as varieties,
yield fewer seeds when crossed than is natural to the parent-species. Other
varieties have had their reproductive powers so far modified that they are
either more or less fertile than are their parents, when crossed with a
distinct species.
Nevertheless, the fact remains indisputable that domesticated varieties of
animals and of plants, which differ greatly from each other in structure, but
which are certainly descended from the same aboriginal species, such as the
races of the fowl, pigeon, many vegetables, and a host of other productions,
are extremely fertile when crossed; and this seems to make a broad and
impassable barrier between domestic varieties and natural species. But, as I
will now attempt to show, the distinction is not so great and
overwhelmingly important as it at first appears.

On the Difference in Fertility between Varieties and Species when crossed.
This work is not the proper place for fully treating the subject of hybridism,
and I have already given in my 'Origin of Species' a moderately full
abstract. I will here merely enumerate the general conclusions which may
be relied on, and which bear on our present point.
Firstly, the laws governing the production of hybrids are identical, or nearly
identical, in the animal and vegetable kingdoms.
Secondly, the sterility of distinct species when first united, and that of their
hybrid offspring, graduates, by an almost infinite number of steps, from
zero, when the ovule is never impregnated and a seed-capsule is never
formed, up to complete fertility. We can only escape the conclusion that
some species are fully fertile when crossed, by determining to designate as
varieties all the forms which are quite fertile. This high degree of fertility is,
however, rare. Nevertheless plants, which have been exposed to unnatural
conditions, sometimes become modified in so peculiar a manner, that they
are much more fertile when crossed by a distinct species than when
fertilised by their own pollen. Success in effecting a first union between two

species, and the fertility of their hybrids, depends in an eminent degree on
the conditions of life being favourable. The innate sterility of hybrids of the
same parentage and raised from the same seed-capsule often differs much in
degree.
Thirdly, the degree of sterility of a first cross between two species does not
always run strictly parallel with that of their hybrid offspring. Many cases
are known of species which can be crossed with ease, but yield hybrids
excessively sterile; and conversely some which can be crossed with great
difficulty, but produce fairly fertile hybrids. This is an inexplicable fact, on
the view that species have been specially endowed with mutual sterility in
order to keep them distinct.
Fourthly, the degree of sterility often differs greatly in two species when
reciprocally crossed; for the first will readily fertilise the second; but the
latter is incapable, after hundreds of trials, of fertilising the former. Hybrids
produced from reciprocal crosses between the same two species, likewise
sometimes differ in their degree of sterility. These cases also are utterly
inexplicable on the view of sterility being a special endowment.
Fifthly, the degree of sterility of first crosses and of hybrids runs, to a
certain extent, parallel with the general or systematic affinity of the forms
which are united. For species belonging to distinct genera can rarely, and
those belonging to distinct families can never, be crossed. The parallelism,
however, is far from complete; for a multitude of closely allied species will
not unite, or unite with extreme difficulty, whilst other species, widely
different from each other, can be crossed with perfect facility. Nor does the
difficulty depend on ordinary constitutional differences, for annual and
perennial plants, deciduous and evergreen trees, plants flowering at
different seasons, inhabiting different stations, and naturally living under
the most opposite climates, can often be crossed with ease. The difficulty or
facility apparently depends exclusively on the sexual constitution of the
species which are crossed; or on their sexual elective affinity, i. e.
Wahlverwandtschaft of Gärtner. As species rarely or never become modified
in one character, without being at the same time modified in many, and as
systematic affinity includes all visible resemblances and dissimilarities, any
difference in sexual constitution between two species would naturally stand
in more or less close relation with their systematic position.

Sixthly, the sterility of species when first crossed, and that of hybrids, may
possibly depend to a certain extent on distinct causes. With pure species the
reproductive organs are in a perfect condition, whilst with hybrids they are
often plainly deteriorated. A hybrid embryo which partakes of the
constitution of its father and mother is exposed to unnatural conditions, as
long as it is nourished within the womb, or egg, or seed of the mother-form;
and as we know that unnatural conditions often induce sterility, the
reproductive organs of the hybrid might at this early age be permanently
affected. But this cause has no bearing on the infertility of first unions. The
diminished number of the offspring from first unions may often result, as is
certainly sometimes the case, from the premature death of most of the
hybrid embryos. But we shall immediately see that a law of an unknown
nature apparently exists, which causes the offspring from unions, which are
infertile, to be themselves more or less infertile; and this at present is all
that can be said.
Seventhly, hybrids and mongrels present, with the one great exception of
fertility, the most striking accordance in all other respects; namely, in the
laws of their resemblance to their two parents, in their tendency to
reversion, in their variability, and in being absorbed through repeated
crosses by either parent-form.
Since arriving at the foregoing conclusions, condensed from my former
work, I have been led to investigate a subject which throws considerable
light on hybridism, namely, the fertility of reciprocally dimorphic and
trimorphic plants, when illegitimately united. I have had occasion several
times to allude to these plants, and I may here give a brief abstract[441] of
my observations. Several plants belonging to distinct orders present two
forms, which exist in about equal numbers, and which differ in no respect
except in their reproductive organs; one form having a long pistil with short
stamens, the other a short pistil with long stamens; both with differently
sized pollen-grains. With trimorphic plants there are three forms likewise
differing in the lengths of their pistils and stamens, in the size and colour of
the pollen-grains, and in some other respects; and as in each of the three
forms there are two sets of stamens, there are altogether six sets of stamens
and three kinds of pistils. These organs are so proportioned in length to each
other that, in any two of the forms, half the stamens in each stand on a level
with the stigma of the third form. Now I have shown, and the result has

been confirmed by other observers, that, in order to obtain full fertility with
these plants, it is necessary that the stigma of the one form should be
fertilised by pollen taken from the stamens of corresponding height in the
other form. So that with dimorphic species two unions, which may be called
legitimate, are fully fertile, and two, which may be called illegitimate, are
more or less infertile. With trimorphic species six unions are legitimate or
fully fertile, and twelve are illegitimate or more or less infertile.
The infertility which may be observed in various dimorphic and trimorphic
plants, when they are illegitimately fertilised, that is, by pollen taken from
stamens not corresponding in height with the pistil, differs much in degree,
up to absolute and utter sterility; just in the same manner as occurs in
crossing distinct species. As the degree of sterility in the latter case depends
in an eminent degree on the conditions of life being more or less
favourable, so I have found it with illegitimate unions. It is well known that
if pollen of a distinct species be placed on the stigma of a flower, and its
own pollen be afterwards, even after a considerable interval of time, placed
on the same stigma, its action is so strongly prepotent that it generally
annihilates the effect of the foreign pollen; so it is with the pollen of the
several forms of the same species, for legitimate pollen is strongly
prepotent over illegitimate pollen, when both are placed on the same
stigma. I ascertained this by fertilising several flowers, first illegitimately,
and twenty-four hours afterwards legitimately, with pollen taken from a
peculiarly coloured variety, and all the seedlings were similarly coloured;
this shows that the legitimate pollen, though applied twenty-four hours
subsequently, had wholly destroyed or prevented the action of the
previously applied illegitimate pollen. Again, as, in making reciprocal
crosses between the same two species, there is occasionally a great
difference in the result, so something analogous occurs with dimorphic
plants; for a short-styled cowslip (P. veris) yields more seed when fertilised
by the long-styled form, and less seed when fertilised by its own form,
compared with a long-styled cowslip when fertilised in the two
corresponding methods.
In all these respects the forms of the same undoubted species, when
illegitimately united, behave in exactly the same manner as do two distinct
species when crossed. This led me carefully to observe during four years
many seedlings, raised from several illegitimate unions. The chief result is

that these illegitimate plants, as they may be called, are not fully fertile. It is
possible to raise from dimorphic species, both long-styled and short-styled
illegitimate plants, and from trimorphic plants all three illegitimate forms.
These can then be properly united in a legitimate manner. When this is
done, there is no apparent reason why they should not yield as many seeds
as did their parents when legitimately fertilised. But such is not the case;
they are all infertile, but in various degrees; some being so utterly and
incurably sterile that they did not yield during four seasons a single seed or
even seed-capsule. These illegitimate plants, which are so sterile, although
united with each other in a legitimate manner, may be strictly compared
with hybrids when crossed inter se, and it is well known how sterile these
latter generally are. When, on the other hand, a hybrid is crossed with either
pure parent-species, the sterility is usually much lessened: and so it is when
an illegitimate plant is fertilised by a legitimate plant. In the same manner
as the sterility of hybrids does not always run parallel with the difficulty of
making the first cross between the two parent species, so the sterility of
certain illegitimate plants was unusually great, whilst the sterility of the
union from which they were derived was by no means great. With hybrids
raised from the same seed-capsule the degree of sterility is innately
variable, so it is in a marked manner with illegitimate plants. Lastly, many
hybrids are profuse and persistent flowerers, whilst other and more sterile
hybrids produce few flowers, and are weak, miserable dwarfs; exactly
similar cases occur with the illegitimate offspring of various dimorphic and
trimorphic plants.
Altogether there is the closest identity in character and behaviour between
illegitimate plants and hybrids. It is hardly an exaggeration to maintain that
the former are hybrids, but produced within the limits of the same species
by the improper union of certain forms, whilst ordinary hybrids are
produced from an improper union between so-called distinct species. We
have already seen that there is the closest similarity in all respects between
first illegitimate unions, and first crosses between distinct species. This will
perhaps be made more fully apparent by an illustration: we may suppose
that a botanist found two well-marked varieties (and such occur) of the
long-styled form of the trimorphic Lythrum salicaria, and that he
determined to try by crossing whether they were specifically distinct. He
would find that they yielded only about one-fifth of the proper number of

seed, and that they behaved in all the other above-specified respects as if
they had been two distinct species. But to make the case sure, he would
raise plants from his supposed hybridised seed, and he would find that the
seedlings were miserably dwarfed and utterly sterile, and that they behaved
in all other respects like ordinary hybrids. He might then maintain that he
had actually proved, in accordance with the common view, that his two
varieties were as good and as distinct species as any in the world; but he
would be completely mistaken.
The facts now given on dimorphic and trimorphic plants are important,
because they show us, firstly, that the physiological test of lessened fertility,
both in first crosses and in hybrids, is no safe criterion of specific
distinction; secondly, because we may conclude that there must be some
unknown law or bond connecting the infertility of illegitimate unions with
that of their illegitimate offspring, and we are thus led to extend this view to
first crosses and hybrids; thirdly, because we find, and this seems to me of
especial importance, that with trimorphic plants three forms of the same
species exist, which when crossed in a particular manner are infertile, and
yet these forms differ in no respect from each other, except in their
reproductive organs,—as in the relative length of the stamens and pistils, in
the size, form, and colour of the pollen-grains, in the structure of the stigma,
and in, the number and size of the seeds. With these differences and no
others, either in organisation or constitution, we find that the illegitimate
unions and the illegitimate progeny of these three forms are more or less
sterile, and closely resemble in a whole series of relations the first unions
and hybrid offspring of distinct species. From this we may infer that the
sterility of species when crossed and of their hybrid progeny is likewise in
all probability exclusively due to differences confined to the reproductive
system. We have indeed been brought to a similar conclusion by observing
that the sterility of crossed species does not strictly coincide with their
systematic affinity, that is, with the sum of their external resemblances; nor
does it coincide with their similarity in general constitution. But we are
more especially led to this same conclusion by considering reciprocal
crosses, in which the male of one species cannot be united, or can be united
with extreme difficulty, with the female of a second species, whilst the
converse cross can be effected with perfect facility; for this difference in the
facility of making reciprocal crosses, and in the fertility of their offspring,

must be attributed either to the male or female element in the first species
having been differentiated with reference to the sexual element of the
second species in a higher degree than in the converse case. In so complex a
subject as Hybridism it is of considerable importance thus to arrive at a
definitive conclusion, namely, that the sterility which almost invariably
follows the union of distinct species depends exclusively on differences in
their sexual constitution.

On the principle which makes it necessary for man, whilst he is selecting
and improving his domestic varieties, to keep them separate, it would
clearly be advantageous to varieties in a state of nature, that is to incipient
species, if they could be kept from blending, either through sexual aversion,
or by becoming mutually sterile. Hence it at one time appeared to me
probable, as it has to others, that this sterility might have been acquired
through natural selection. On this view we must suppose that a shade of
lessened fertility first spontaneously appeared, like any other modification,
in certain individuals of a species when crossed with other individuals of
the same species; and that successive slight degrees of infertility, from
being advantageous, were slowly accumulated. This appears all the more
probable, if we admit that the structural differences between the forms of
dimorphic and trimorphic plants, as the length and curvature of the pistil,
&c., have been co-adapted through natural selection; for if this be admitted,
we can hardly avoid extending the same conclusion to their mutual
infertility. Sterility moreover has been acquired through natural selection
for other and widely different purposes, as with neuter insects in reference
to their social economy. In the case of plants, the flowers on the
circumference of the truss in the guelder-rose (Viburnum opulus) and those
on the summit of the spike in the feather-hyacinth (Muscari comosum) have
been rendered conspicuous, and apparently in consequence sterile, in order
that insects might easily discover and visit the other flowers. But when we
endeavour to apply the principle of natural selection to the acquirement by
distinct species of mutual sterility, we meet with great difficulties. In the
first place, it may be remarked that separate regions are often inhabited by
groups of species or by single species, which when brought together and
crossed are found to be more or less sterile; now it could clearly have been
of no advantage to such separated species to have been rendered mutually
sterile, and consequently this could not have been effected through natural

selection; but it may perhaps be argued, that, if a species were rendered
sterile with some one compatriot, sterility with other species would follow
as a necessary consequence. In the second place, it is as much opposed to
the theory of natural selection, as to the theory of special creation, that in
reciprocal crosses the male element of one form should have been rendered
utterly impotent on a second form, whilst at the same time the male element
of this second form is enabled freely to fertilise the first form; for this
peculiar state of the reproductive system could not possibly be
advantageous to either species.
In considering the probability of natural selection having come into action
in rendering species mutually sterile, one great difficulty will be found to lie
in the existence of many graduated steps from slightly lessened fertility to
absolute sterility. It may be admitted, on the principle above explained, that
it would profit an incipient species if it were rendered in some slight degree
sterile when crossed with its parent-form or with some other variety; for
thus fewer bastardised and deteriorated offspring would be produced to
commingle their blood with the new species in process of formation. But he
who will take the trouble to reflect on the steps by which this first degree of
sterility could be increased through natural selection to that higher degree
which is common to so many species, and which is universal with species
which have been differentiated to a generic or family rank, will find the
subject extraordinarily complex. After mature reflection it seems to me that
this could not have been effected through natural selection; for it could have
been of no direct advantage to an individual animal to breed badly with
another individual of a different variety, and thus leave few offspring;
consequently such individuals could not have been preserved or selected.
Or take the case of two species which in their present state, when crossed,
produce few and sterile offspring; now, what is there which could favour
the survival of those individuals which happened to be endowed in a
slightly higher degree with mutual infertility and which thus approached by
one small step towards absolute sterility? yet an advance of this kind, if the
theory of natural selection be brought to bear, must have incessantly
occurred with many species, for a multitude are mutually quite barren. With
sterile neuter insects we have reason to believe that modifications in their
structure have been slowly accumulated by natural selection, from an
advantage having been thus indirectly given to the community to which

they belonged over other communities of the same species; but an
individual animal, if rendered slightly sterile when crossed with some other
variety, would not thus in itself gain any advantage, or indirectly give any
advantage to its nearest relatives or to other individuals of the same variety,
leading to their preservation. I infer from these considerations that, as far as
animals are concerned, the various degrees of lessened fertility which occur
with species when crossed cannot have been slowly accumulated by means
of natural selection.
With plants, it is possible that the case may be somewhat different. With
many kinds, insects constantly carry pollen from neighbouring plants to the
stigmas of each flower; and with some species this is effected by the wind.
Now, if the pollen of a variety, when deposited on the stigma of the same
variety, should become by spontaneous variation in ever so slight a degree
prepotent over the pollen of other varieties, this would certainly be an
advantage to the variety; for its own pollen would thus obliterate the effects
of the pollen of other varieties, and prevent deterioration of character. And
the more prepotent the variety's own pollen could be rendered through
natural selection, the greater the advantage would be. We know from the
researches of Gärtner that, with species which are mutually sterile, the
pollen of each is always prepotent on its own stigma over that of the other
species; but we do not know whether this prepotency is a consequence of
the mutual sterility, or the sterility a consequence of the prepotency. If the
latter view be correct, as the prepotency became stronger through natural
selection, from being advantageous to a species in process of formation, so
the sterility consequent on prepotency would at the same time be
augmented; and the final result would be various degrees of sterility, such
as occurs with existing species. This view might be extended to animals, if
the female before each birth received several males, so that the sexual
element of the prepotent male of her own variety obliterated the effects of
the access of previous males belonging to other varieties; but we have no
reason to believe, at least with terrestrial animals, that this is the ease; as
most males and females pair for each birth, and some few for life.
On the whole we may conclude that with animals the sterility of crossed
species has not been slowly augmented through natural selection; and as
this sterility follows the same general laws in the vegetable as in the animal
kingdom, it is improbable, though apparently possible, that with plants

crossed species should have been rendered sterile by a different process.
From this consideration, and remembering that species which have never
co-existed in the same country, and which therefore could not have received
any advantage from having been rendered mutually infertile, yet are
generally sterile when crossed; and bearing in mind that in reciprocal
crosses between the same two species there is sometimes the widest
difference in their sterility, we must give up the belief that natural selection
has come into play.
As species have not been rendered mutually infertile through the
accumulative action of natural selection, and as we may safely conclude,
from the previous as well as from other and more general considerations,
that they have not been endowed through an act of creation with this
quality, we must infer that it has arisen incidentally during their slow
formation in connection with other and unknown changes in their
organisation. By a quality arising incidentally, I refer to such cases as
different species of animals and plants being differently affected by poisons
to which they are not naturally exposed; and this difference in susceptibility
is clearly incidental on other and unknown differences in their organisation.
So again the capacity in different kinds of trees to be grafted on each other,
or on a third species, differs much, and is of no advantage to these trees, but
is incidental on structural or functional differences in their woody tissues.
We need not feel surprise at sterility incidentally resulting from crosses
between distinct species,—the modified descendants of a common
progenitor,—when we bear in mind how easily the reproductive system is
affected by various causes—often by extremely slight changes in the
conditions of life, by too close interbreeding, and by other agencies. It is
well to bear in mind such cases, as that of the Passiflora alata, which
recovered its self-fertility from being grafted on a distinct species—the
cases of plants which normally or abnormally are self-impotent, but can
readily be fertilised by the pollen of a distinct species—and lastly the cases
of individual domesticated animals which evince towards each other sexual
incompatibility.

We now at last come to the immediate point under discussion: how is it that,
with some few exceptions in the case of plants, domesticated varieties, such
as those of the dog, fowl, pigeon, several fruit-trees, and culinary

vegetables, which differ from each other in external characters more than
many species, are perfectly fertile when crossed, or even fertile in excess,
whilst closely allied species are almost invariably in some degree sterile?
We can, to a certain extent, give a satisfactory answer to this question.
Passing over the fact that the amount of external difference between two
species is no sure guide to their degree of mutual sterility, so that similar
differences in the case of varieties would be no sure guide, we know that
with species the cause lies exclusively in differences in their sexual
constitution. Now the conditions to which domesticated animals and
cultivated plants have been subjected, have had so little tendency towards
modifying the reproductive system in a manner leading to mutual sterility,
that we have good grounds for admitting the directly opposite doctrine of
Pallas, namely, that such conditions generally eliminate this tendency; so
that the domesticated descendants of species, which in their natural state
would have been in some degree sterile when crossed, become perfectly
fertile together. With plants, so far is cultivation from giving a tendency
towards mutual sterility, that in several well-authenticated cases, already
often alluded to, certain species have been affected in a very different
manner, for they have become self-impotent, whilst still retaining the
capacity of fertilising, and being fertilised by, distinct species. If the
Pallasian doctrine of the elimination of sterility through long-continued
domestication be admitted, and it can hardly be rejected, it becomes in the
highest degree improbable that similar circumstances should commonly
both induce and eliminate the same tendency; though in certain cases, with
species having a peculiar constitution, sterility might occasionally be thus
induced. Thus, as I believe, we can understand why with domesticated
animals varieties have not been produced which are mutually sterile; and
why with plants only a few such cases have been observed, namely, by
Gärtner, with certain varieties of maize and verbascum, by other
experimentalists with varieties of the gourd and melon, and by Kölreuter
with one kind of tobacco.
With respect to varieties which have originated in a state of nature, it is
almost hopeless to expect to prove by direct evidence that they have been
rendered mutually sterile; for if even a trace of sterility could be detected,
such varieties would at once be raised by almost every naturalist to the rank
of distinct species. If, for instance, Gärtner's statement were fully

confirmed, that the blue and red-flowered forms of the pimpernel (Anagallis
arvensis) are sterile when crossed, I presume that all the botanists who now
maintain on various grounds that these two forms are merely fleeting
varieties, would at once admit that they were specifically distinct.
The real difficulty in our present subject is not, as it appears to me, why
domestic varieties have not become mutually infertile when crossed, but
why this has so generally occurred with natural varieties as soon as they
have been modified in a sufficient and permanent degree to take rank as
species. We are far from precisely knowing the cause; nor is this surprising,
seeing how profoundly ignorant we are in regard to the normal and
abnormal action of the reproductive system. But we can see that species,
owing to their struggle for life with numerous competitors, must have been
exposed to more uniform conditions during long periods of time, than have
been domestic varieties; and this may well make a wide difference in the
result. For we know how commonly wild animals and plants, when taken
from their natural conditions and subjected to captivity, are rendered sterile;
and the reproductive functions of organic beings which have always lived
and been slowly modified under natural conditions would probably in like
manner be eminently sensitive to the influence of an unnatural cross.
Domesticated productions, on the other hand, which, as shown by the mere
fact of their domestication, were not originally highly sensitive to changes
in their conditions of life, and which can now generally resist with
undiminished fertility repeated changes of conditions, might be expected to
produce varieties, which would be little liable to have their reproductive
powers injuriously affected by the act of crossing with other varieties which
had originated in a like manner.
Certain naturalists have recently laid too great stress, as it appears to me, on
the difference in fertility between varieties and species when crossed. Some
allied species of trees cannot be grafted on each other,—all varieties can be
so grafted. Some allied animals are affected in a very different manner by
the same poison, but with varieties no such case until recently was known,
but now it has been proved that immunity from certain poisons stands in
some cases in correlation with the colour of the hair. The period of gestation
generally differs much with distinct species, but with varieties until lately
no such difference had been observed. The time required for the
germination of seeds differs in an analogous manner, and I am not aware

that any difference in this respect has as yet been detected with varieties.
Here we have various physiological differences, and no doubt others could
be added, between one species and another of the same genus, which do not
occur, or occur with extreme rarity, in the case of varieties; and these
differences are apparently wholly or in chief part incidental on other
constitutional differences, just in the same manner as the sterility of crossed
species is incidental on differences confined to the sexual system. Why,
then, should these latter differences, however serviceable they may
indirectly be in keeping the inhabitants of the same country distinct, be
thought of such paramount importance, in comparison with other incidental
and functional differences? No sufficient answer to this question can be
given. Hence the fact that the most distinct domestic varieties are, with rare
exceptions, perfectly fertile when crossed, and produce fertile offspring,
whilst closely allied species are, with rare exceptions, more or less sterile, is
not nearly so formidable an objection as it appears at first to the theory of
the common descent of allied species.

CHAPTER XX.

SELECTION BY MAN.

SELECTION A DIFFICULT ART—METHODICAL, UNCONSCIOUS, AND NATURAL
SELECTION—RESULTS OF METHODICAL SELECTION—CARE TAKEN IN
SELECTION—SELECTION WITH PLANTS—SELECTION CARRIED ON BY THE
ANCIENTS, AND BY SEMI-CIVILIZED PEOPLE—UNIMPORTANT CHARACTERS
OFTEN ATTENDED TO—UNCONSCIOUS SELECTION—AS CIRCUMSTANCES
SLOWLY CHANGE, SO HAVE OUR DOMESTICATED ANIMALS CHANGED
THROUGH THE ACTION OF UNCONSCIOUS SELECTION—INFLUENCE OF
DIFFERENT BREEDERS ON THE SAME SUB-VARIETY—PLANTS AS AFFECTED BY
UNCONSCIOUS SELECTION—EFFECTS OF SELECTION AS SHOWN BY THE
GREAT AMOUNT OF DIFFERENCE IN THE PARTS MOST VALUED BY MAN.

The power of Selection, whether exercised by man, or brought into play
under nature through the struggle for existence and the consequent survival
of the fittest, absolutely depends on the variability of organic beings.
Without variability nothing can be effected; slight individual differences,

however, suffice for the work, and are probably the sole differences which
are effective in the production of new species. Hence our discussion on the
causes and laws of variability ought in strict order to have preceded our
present subject, as well as the previous subjects of inheritance, crossing,
&c.; but practically the present arrangement has been found the most
convenient. Man does not attempt to cause variability; though he
unintentionally effects this by exposing organisms to new conditions of life,
and by crossing breeds already formed. But variability being granted, he
works wonders. Unless some degree of selection be exercised, the free
commingling of the individuals of the same variety soon obliterates, as we
have previously seen, the slight differences which may arise, and gives to
the whole body of individuals uniformity of character. In separated districts,
long-continued exposure to different conditions of life may perhaps produce
new races without the aid of selection; but to this difficult subject of the
direct action of the conditions of life we shall in a future chapter recur.
When animals or plants are born with some conspicuous and firmly
inherited new character, selection is reduced to the preservation of such
individuals, and to the subsequent prevention of crosses; so that nothing
more need be said on the subject. But in the great majority of cases a new
character, or some superiority in an old character, is at first faintly
pronounced, and is not strongly inherited; and then the full difficulty of
selection is experienced. Indomitable patience, the finest powers of
discrimination, and sound judgment must be exercised during many years.
A clearly predetermined object must be kept steadily in view. Few men are
endowed with all these qualities, especially with that of discriminating very
slight differences; judgment can be acquired only by long experience; but if
any of these qualities be wanting, the labour of a life may be thrown away. I
have been astonished when celebrated breeders, whose skill and judgment
have been proved by their success at exhibitions, have shown me their
animals, which appeared all alike, and have assigned their reasons for
matching this and that individual. The importance of the great principle of
Selection mainly lies in this power of selecting scarcely appreciable
differences, which nevertheless are found to be transmissible, and which
can be accumulated until the result is made manifest to the eyes of every
beholder.

The principle of selection may be conveniently divided into three kinds.
Methodical selection is that which guides a man who systematically
endeavours to modify a breed according to some predetermined standard.
Unconscious selection is that which follows from men naturally preserving
the most valued and destroying the less valued individuals, without any
thought of altering the breed; and undoubtedly this process slowly works
great changes. Unconscious selection graduates into methodical, and only
extreme cases can be distinctly separated; for he who preserves a useful or
perfect animal will generally breed from it with the hope of getting
offspring of the same character; but as long as he has not a predetermined
purpose to improve the breed, he may be said to be selecting unconsciously.
[442] Lastly, we have Natural selection, which implies that the individuals

which are best fitted for the complex, and in the course of ages changing
conditions to which they are exposed, generally survive and procreate their
kind. With domestic productions, with which alone we are here strictly
concerned, natural selection comes to a certain extent into action,
independently of, and even in opposition to, the will of man.

Methodical Selection.—What man has effected within recent times in
England by methodical selection is clearly shown by our exhibitions of
improved quadrupeds and fancy birds. With respect to cattle, sheep, and
pigs, we owe their great improvement to a long series of well-known names
—Bakewell, Colling, Ellman, Bates, Jonas Webb, Lords Leicester and
Western, Fisher Hobbs, and others. Agricultural writers are unanimous on
the power of selection: any number of statements to this effect could be
quoted; a few will suffice. Youatt, a sagacious and experienced observer,
writes,[443] the principle of selection is "that which enables the agriculturist,
not only to modify the character of his flock, but to change it altogether." A
great breeder of shorthorns[444] says, "In the anatomy of the shoulder
modern breeders have made great improvements on the Ketton shorthorns
by correcting the defect in the knuckle or shoulder-joint, and by laying the
top of the shoulder more snugly into the crop, and thereby filling up the
hollow behind it.... The eye has its fashion at different periods: at one time
the eye high and outstanding from the head, and at another time the sleepy
eye sunk into the head; but these extremes have merged into the medium of
a full, clear, and prominent eye with a placid look."

Again, hear what an excellent judge of pigs[445] says: "The legs should be
no longer than just to prevent the animal's belly from trailing on the ground.
The leg is the least profitable portion of the hog, and we therefore require
no more of it than is absolutely necessary for the support of the rest." Let
any one compare the wild-boar with any improved breed, and he will see
how effectually the legs have been shortened.
Few persons, except breeders, are aware of the systematic care taken in
selecting animals, and of the necessity of having a clear and almost
prophetic vision into futurity. Lord Spencer's skill and judgment were well
known; and he writes,[446] "It is therefore very desirable, before any man
commences to breed either cattle or sheep, that he should make up his mind
to the shape and qualities he wishes to obtain, and steadily pursue this
object." Lord Somerville, in speaking of the marvellous improvement of the
New Leicester sheep, effected by Bakewell and his successors, says, "It
would seem as if they had first drawn a perfect form, and then given it life."
Youatt[447] urges the necessity of annually drafting each flock, as many
animals will certainly degenerate "from the standard of excellence, which
the breeder has established in his own mind." Even with a bird of such little
importance as the canary, long ago (1780-1790) rules were established, and
a standard of perfection was fixed, according to which the London fanciers
tried to breed the several sub-varieties.[448] A great winner of prizes at the
Pigeon-shows,[449] in describing the Short-faced Almond Tumbler, says,
"There are many first-rate fanciers who are particularly partial to what is
called the goldfinch-beak, which is very beautiful; others say, take a full-
size round cherry, then take a barley-corn, and judiciously placing and
thrusting it into the cherry, form as it were your beak; and that is not all, for
it will form a good head and beak, provided, as I said before, it is
judiciously done; others take an oat; but as I think the goldfinch-beak the
handsomest, I would advise the inexperienced fancier to get the head of a
goldfinch, and keep it by him for his observation." Wonderfully different as
is the beak of the rock-pigeon and goldfinch, undoubtedly, as far as external
shape and proportions are concerned, the end has been nearly gained.
Not only should our animals be examined with the greatest care whilst
alive, but, as Anderson remarks,[450] their carcases should be scrutinised,
"so as to breed from the descendants of such only as, in the language of the

butcher, cut up well." The "grain of the meat" in cattle, and its being well
marbled with fat,[451] and the greater or less accumulation of fat in the
abdomen of our sheep, have been attended to with success. So with poultry,
a writer,[452] speaking of Cochin-China fowls, which are said to differ much
in the quality of their flesh, says, "the best mode is to purchase two young
brother-cocks, kill, dress, and serve up one; if he be indifferent, similarly
dispose of the other, and try again; if, however, he be fine and well-
flavoured, his brother will not be amiss for breeding purposes for the table."
The great principle of the division of labour has been brought to bear on
selection. In certain districts[453] "the breeding of bulls is confined to a very
limited number of persons, who by devoting their whole attention to this
department, are able from year to year to furnish a class of bulls which are
steadily improving the general breed of the district." The rearing and letting
of choice rams has long been, as is well known, a chief source of profit to
several eminent breeders. In parts of Germany this principle is carried with
merino sheep to an extreme point.[454] "So important is the proper selection
of breeding animals considered, that the best flock-masters do not trust to
their own judgment, or to that of their shepherds, but employ persons called
'sheep-classifiers,' who make it their special business to attend to this part of
the management of several flocks, and thus to preserve, or if possible to
improve, the best qualities of both parents in the lambs." In Saxony, "when
the lambs are weaned, each in his turn is placed upon a table that his wool
and form may be minutely observed. The finest are selected for breeding
and receive a first mark. When they are one year old, and prior to shearing
them, another close examination of those previously marked takes place:
those in which no defect can be found receive a second mark, and the rest
are condemned. A few months afterwards a third and last scrutiny is made;
the prime rams and ewes receive a third and final mark, but the slightest
blemish is sufficient to cause the rejection of the animal." These sheep are
bred and valued almost exclusively for the fineness of their wool; and the
result corresponds with the labour bestowed on their selection. Instruments
have been invented to measure accurately the thickness of the fibres; and
"an Austrian fleece has been produced of which twelve hairs equalled in
thickness one from a Leicester sheep."

Throughout the world, wherever silk is produced, the greatest care is
bestowed on selecting the cocoons from which the moths for breeding are
to be reared. A careful cultivator[455] likewise examines the moths
themselves, and destroys those that are not perfect. But what more
immediately concerns us is that certain families in France devote
themselves to raising eggs for sale.[456] In China, near Shanghai, the
inhabitants of two small districts have the privilege of raising eggs for the
whole surrounding country, and that they may give up their whole time to
this business, they are interdicted by law from producing silk.[457]
The care which successful breeders take in matching their birds is
surprising. Sir John Sebright, whose fame is perpetuated by the "Sebright
Bantam," used to spend "two and three days in examining, consulting, and
disputing with a friend which were the best of five or six birds."[458] Mr.
Bult, whose pouter-pigeons won so many prizes and were exported to North
America under the charge of a man sent on purpose, told me that he always
deliberated for several days before he matched each pair. Hence we can
understand the advice of an eminent fancier, who writes,[459] "I would here
particularly guard you against having too great a variety of pigeons,
otherwise you will know a little of all, but nothing about one as it ought to
be known." Apparently it transcends the power of the human intellect to
breed all kinds: "it is possible that there may be a few fanciers that have a
good general knowledge of fancy pigeons; but there are many more who
labour under the delusion of supposing they know what they do not." The
excellence of one sub-variety, the Almond Tumbler, lies in the plumage,
carriage, head, beak, and eye; but it is too presumptuous in the beginner to
try for all these points. The great judge above quoted says, "there are some
young fanciers who are over-covetous, who go for all the above five
properties at once; they have their reward by getting nothing." We thus see
that breeding even fancy pigeons is no simple art: we may smile at the
solemnity of these precepts, but he who laughs will win no prizes.
What methodical selection has effected for our animals is sufficiently
proved, as already remarked, by our Exhibitions. So greatly were the sheep
belonging to some of the earlier breeders, such as Bakewell and Lord
Western, changed, that many persons could not be persuaded that they had
not been crossed. Our pigs, as Mr. Corringham remarks,[460] during the last

twenty years have undergone, through rigorous selection together with
crossing, a complete metamorphosis. The first exhibition for poultry was
held in the Zoological Gardens in 1845; and the improvement effected since
that time has been great. As Mr. Baily, the great judge, remarked to me, it
was formerly ordered that the comb of the Spanish cock should be upright,
and in four or five years all good birds had upright combs; it was ordered
that the Polish cock should have no comb or wattles, and now a bird thus
furnished would be at once disqualified; beards were ordered, and out of
fifty-seven pens lately (1860) exhibited at the Crystal Palace, all had beards.
So it has been in many other cases. But in all cases the judges order only
what is occasionally produced and what can be improved and rendered
constant by selection. The steady increase of weight during the last few
years in our fowls, turkeys, ducks, and geese is notorious; "six-pound ducks
are now common, whereas four pounds was formerly the average." As the
actual time required to make a change has not often been recorded, it may
be worth mentioning that it took Mr. Wicking thirteen years to put a clean
white head on an almond tumbler's body, "a triumph," says another fancier,
"of which he may be justly proud."[461]
Mr. Tollet, of Betley Hall, selected cows, and especially bulls, descended
from good milkers, for the sole purpose of improving his cattle for the
production of cheese; he steadily tested the milk with the lactometer, and in
eight years he increased, as I was informed by him, the product in the
proportion of four to three. Here is a curious case[462] of steady but slow
progress, with the end not as yet fully attained: in 1784 a race of silkworms
was introduced into France, in which one hundred out of the thousand failed
to produce white cocoons; but now, after careful selection during sixty-five
generations, the proportion of yellow cocoons has been reduced to thirty-
five in the thousand.
With plants selection has been followed with the same good results as with
animals. But the process is simpler, for plants in the great majority of cases
bear both sexes. Nevertheless, with most kinds it is necessary to take as
much care to prevent crosses as with animals or unisexual plants; but with
some plants, such as peas, this care does not seem to be necessary. With all
improved plants, excepting of course those which are propagated by buds,
cuttings, &c., it is almost indispensable to examine the seedlings and
destroy those which depart from the proper type. This is called "roguing,"

and is, in fact, a form of selection, like the rejection of inferior animals.
Experienced horticulturists and agriculturists incessantly urge every one to
preserve the finest plants for the production of seed.
Although plants often present much more conspicuous variations than
animals, yet the closest attention is generally requisite to detect each slight
and favourable change. Mr. Masters relates[463] how "many a patient hour
was devoted," whilst he was young, to the detection of differences in peas
intended for seed. Mr. Barnet[464] remarks that the old scarlet American
strawberry was cultivated for more than a century without producing a
single variety; and another writer observes how singular it was that when
gardeners first began to attend to this fruit it began to vary; the truth no
doubt being that it had always varied, but that, until slight varieties were
selected and propagated by seed, no conspicuous result was obtained. The
finest shades of difference in wheat have been discriminated and selected
with almost as much care, as we see in Colonel Le Couteur's works, as in
the case of the higher animals; but with our cereals the process of selection
has seldom or never been long continued.
It may be worth while to give a few examples of methodical selection with
plants; but in fact the great improvement of all our anciently cultivated
plants may be attributed to selection long carried on, in part methodically,
and in part unconsciously. I have shown in a former chapter how the weight
of the gooseberry has been increased by systematic selection and culture.
The flowers of the Heartsease have been similarly increased in size and
regularity of outline. With the Cineraria, Mr. Glenny[465] "was bold enough,
when the flowers were ragged and starry and ill defined in colour, to fix a
standard which was then considered outrageously high and impossible, and
which, even if reached, it was said, we should be no gainers by, as it would
spoil the beauty of the flowers. He maintained that he was right; and the
event has proved it to be so." The doubling of flowers has several times
been effected by careful selection: the Rev. W. Williamson,[466] after sowing
during several years seed of Anemone coronaria, found a plant with one
additional petal; he sowed the seed of this, and by perseverance in the same
course obtained several varieties with six or seven rows of petals. The
single Scotch rose was doubled, and yielded eight good varieties in nine or
ten years.[467] The Canterbury bell (Campanula medium) was doubled by

careful selection in four generations.[468] In four years Mr. Buckman,[469] by
culture and careful selection, converted parsnips, raised from wild seed, into
a new and good variety. By selection during a long course of years, the
early maturity of peas has been hastened from ten to twenty-one days.[470] A
more curious case is offered by the beet-plant, which, since its cultivation in
France, has almost exactly doubled its yield of sugar. This has been effected
by the most careful selection; the specific gravity of the roots being
regularly tested, and the best roots saved for the production of seed.[471]

Selection by Ancient and Semi-civilised People.
In attributing so much importance to the selection of animals and plants, it
may be objected that methodical selection would not have been carried on
during ancient times. A distinguished naturalist considers it as absurd to
suppose that semi-civilised people should have practised selection of any
kind. Undoubtedly the principle has been systematically acknowledged and
followed to a far greater extent within the last hundred years than at any
former period, and a corresponding result has been gained; but it would be a
great error to suppose, as we shall immediately see, that its importance was
not recognised and acted on during the most ancient times, and by semi-
civilised people. I should premise that many facts now to be given only
show that care was taken in breeding; but when this is the case, selection is
almost sure to be practised to a certain extent. We shall hereafter be enabled
better to judge how far selection, when only occasionally carried on, by a
few of the inhabitants of a country, will slowly produce a great effect.
In a well-known passage in the thirtieth chapter of Genesis, rules are given
for influencing, as was then thought possible, the colour of sheep; and
speckled and dark breeds are spoken of as being kept separate. By the time
of David the fleece was likened to snow. Youatt,[472] who has discussed all
the passages in relation to breeding in the Old Testament, concludes that at
this early period "some of the best principles of breeding must have been
steadily and long pursued." It was ordered, according to Moses, that "Thou
shalt not let thy cattle gender with a diverse kind;" but mules were
purchased,[473] so that at this early period other nations must have crossed
the horse and ass. It is said[474] that Erichthonius, some generations before
the Trojan war, had many brood-mares, "which by his care and judgment in

the choice of stallions produced a breed of horses superior to any in the
surrounding countries." Homer (Book v.) speaks of Æneas's horses as bred
from mares which were put to the steeds of Laomedon. Plato, in his
'Republic,' says to Glaucus, "I see that you raise at your house a great many
dogs for the chase. Do you take care about breeding and pairing them?
Among animals of good blood, are there not always some which are
superior to the rest?" To which Glaucus answers in the affirmative.[475]
Alexander the Great selected the finest Indian cattle to send to Macedonia
to improve the breed.[476] According to Pliny,[477] King Pyrrhus had an
especially valuable breed of oxen; and he did not suffer the bulls and cows
to come together till four years old, that the breed might not degenerate.
Virgil, in his Georgics (lib. iii.), gives as strong advice as any modern
agriculturist could do, carefully to select the breeding stock; "to note the
tribe, the lineage, and the sire; whom to reserve for husband of the herd;"—
to brand the progeny;—to select sheep of the purest white, and to examine
if their tongues are swarthy. We have seen that the Romans kept pedigrees
of their pigeons, and this would have been a senseless proceeding had not
great care been taken in breeding them. Columella gives detailed
instructions about breeding fowls: "Let the breeding hens therefore be of a
choice colour, a robust body, square-built, full-breasted, with large heads,
with upright and bright-red combs. Those are believed to be the best bred
which have five toes."[478] According to Tacitus, the Celts attended to the
races of their domestic animals; and Cæsar states that they paid high prices
to merchants for fine imported horses.[479] In regard to plants, Virgil speaks
of yearly culling the largest seeds; and Celsus says, "where the corn and
crop is but small, we must pick out the best ears of corn, and of them lay up
our seed separately by itself."[480]
Coming down the stream of time, we may be brief. At about the beginning
of the ninth century Charlemagne expressly ordered his officers to take
great care of his stallions; and if any proved bad or old, to forewarn him in
good time before they were put to the mares.[481] Even in a country so little
civilised as Ireland during the ninth century, it would appear from some
ancient verses,[482] describing a ransom demanded by Cormac, that animals
from particular places, or having a particular character, were valued. Thus it
is said,—

Two pigs of the pigs of Mac Lir,
A ram and ewe both round and red,
I brought with me from Aengus.
I brought with me a stallion and a mare
From the beautiful stud of Manannan,
A bull and a white cow from Druim Cain.

Athelstan, in 930, received as a present from Germany, running-horses; and
he prohibited the exportation of English horses. King John imported "one
hundred chosen stallions from Flanders."[483] On June 16th, 1305, the
Prince of Wales wrote to the Archbishop of Canterbury, begging for the loan
of any choice stallion, and promising its return at the end of the season.[484]
There are numerous records at ancient periods in English history of the
importation of choice animals of various kinds, and of foolish laws against
their exportation. In the reigns of Henry VII. and VIII. it was ordered that
the magistrates, at Michaelmas, should scour the heaths and commons, and
destroy all mares beneath a certain size.[485] Some of our earlier kings
passed laws against the slaughtering rams of any good breed before they
were seven years old, so that they might have time to breed. In Spain
Cardinal Ximenes issued, in 1509, regulations on the selection of good rams
for breeding.[486]
The Emperor Akbar Khan before the year 1600 is said to have "wonderfully
improved" his pigeons by crossing the breeds; and this necessarily implies
careful selection. About the same period the Dutch attended with the
greatest care to the breeding of these birds. Belon in 1555 says that good
managers in France examined the colour of their goslings in order to get
geese of a white colour and better kinds. Markham in 1631 tells the breeder
"to elect the largest and goodliest conies," and enters into minute details.
Even with respect to seeds of plants for the flower-garden, Sir J. Hanmer
writing about the year 1660[487] says, in "choosing seed, the best seed is the
most weighty, and is had from the lustiest and most vigorous stems;" and he
then gives rules about leaving only a few flowers on plants for seed; so that
even such details were attended to in our flower-gardens two hundred years
ago. In order to show that selection has been silently carried on in places
where it would not have been expected, I may add that in the middle of the
last century, in a remote part of North America, Mr. Cooper improved by

careful selection all his vegetables, "so that they were greatly superior to
those of any other person. When his radishes, for instance, are fit for use, he
takes ten or twelve that he most approves, and plants them at least 100
yards from others that blossom at the same time. In the same manner he
treats all his other plants, varying the circumstances according to their
nature."[488]
In the great work on China published in the last century by the Jesuits, and
which is chiefly compiled from ancient Chinese encyclopædias, it is said
that with sheep "improving the breed consists in choosing with particular
care the lambs which are destined for propagation, in nourishing them well,
and in keeping the flocks separate." The same principles were applied by
the Chinese to various plants and fruit-trees.[489] An imperial edict
recommends the choice of seed of remarkable size; and selection was
practised even by imperial hands, for it is said that the Ya-mi, or imperial
rice, was noticed at an ancient period in a field by the Emperor Khang-hi,
was saved and cultivated in his garden, and has since become valuable from
being the only kind which will grow north of the Great Wall.[490] Even with
flowers, the tree pæony (P. moutan) has been cultivated, according to
Chinese traditions, for 1400 years; between 200 and 300 varieties have been
raised, which are cherished like tulips formerly were by the Dutch.[491]
Turning now to semi-civilised people and to savages: it occurred to me,
from what I had seen of several parts of South America, where fences do
not exist, and where the animals are of little value, that there would be
absolutely no care in breeding or selecting them; and this to a large extent is
true. Roulin,[492] however, describes in Colombia a naked race of cattle,
which are not allowed to increase, on account of their delicate constitution.
According to Azara[493] horses are often born in Paraguay with curly hair;
but, as the natives do not like them, they are destroyed. On the other hand,
Azara states that a hornless bull, born in 1770, was preserved and
propagated its race. I was informed of the existence in Banda Oriental of a
breed with reversed hair; and the extraordinary niata cattle first appeared
and have since been kept distinct in La Plata. Hence certain conspicuous
variations have been preserved, and others have been habitually destroyed,
in these countries, which are so little favourable for careful selection. We
have also seen that the inhabitants sometimes introduce cattle on their

estates to prevent the evil effects of close interbreeding. On the other hand,
I have heard on reliable authority that the Gauchos of the Pampas never
take any pains in selecting the best bulls or stallions for breeding; and this
probably accounts for the cattle and horses being remarkably uniform in
character throughout the immense range of the Argentine republic.
Looking to the Old World, in the Sahara Desert "The Touareg is as careful
in the selection of his breeding Mahari (a fine race of the dromedary) as the
Arab is in that of his horse. The pedigrees are handed down, and many a
dromedary can boast a genealogy far longer than the descendants of the
Darley Arabian."[494] According to Pallas the Mongolians endeavour to
breed the Yaks or horse-tailed buffaloes with white tails, for these are sold
to the Chinese mandarins as fly-flappers; and Moorcroft, about seventy
years after Pallas, found that white-tailed animals were still selected for
breeding.[495]
We have seen in the chapter on the Dog that savages in different parts of
North America and in Guiana cross their dogs with wild Canidæ, as did the
ancient Gauls, according to Pliny. This was done to give their dogs strength
and vigour, in the same way as the keepers in large warrens now sometimes
cross their ferrets (as I have been informed by Mr. Yarrell) with the wild
polecat, "to give them more devil." According to Varro, the wild ass was
formerly caught and crossed with the tame animal to improve the breed, in
the same manner as at the present day the natives of Java sometimes drive
their cattle into the forests to cross with the wild Banteng (Bos sondaicus).
[496] In Northern Siberia, among the Ostyaks the dogs vary in markings in

different districts, but in each place they are spotted black and white in a
remarkably uniform manner;[497] and from this fact alone we may infer
careful breeding, more especially as the dogs of one locality are famed
throughout the country for their superiority. I have heard of certain tribes of
Esquimaux who take pride in their teams of dogs being uniformly coloured.
In Guiana, as Sir R. Schomburgk informs me,[498] the dogs of the Turuma
Indians are highly valued and extensively bartered: the price of a good one
is the same as that given for a wife: they are kept in a sort of cage, and the
Indians "take great care when the female is in season to prevent her uniting
with a dog of an inferior description." The Indians told Sir Robert that, if a
dog proved bad or useless, he was not killed, but was left to die from sheer

neglect. Hardly any nation is more barbarous than the Fuegians, but I hear
from Mr. Bridges, the Catechist to the Mission, that, "when these savages
have a large, strong, and active bitch, they take care to put her to a fine dog,
and even take care to feed her well, that her young may be strong and well
favoured."
In the interior of Africa, negroes, who have not associated with white men,
show great anxiety to improve their animals: they "always choose the larger
and stronger males for stock:" the Malakolo were much pleased at
Livingstone's promise to send them a bull, and some Bakalolo carried a live
cock all the way from Loanda into the interior.[499] Further south on the
same continent, Andersson states that he has known a Damara give two fine
oxen for a dog which struck his fancy. The Damaras take great delight in
having whole droves of cattle of the same colour, and they prize their oxen
in proportion to the size of their horns. "The Namaquas have a perfect
mania for a uniform team; and almost all the people of Southern Africa
value their cattle next to their women, and take a pride in possessing
animals that look high-bred." "They rarely or never make use of a
handsome animal as a beast of burden."[500] The power of discrimination
which these savages possess is wonderful, and they can recognise to which
tribe any cattle belong. Mr. Andersson further informs me that the natives
frequently match a particular bull with a particular cow.
The most curious case of selection by semi-civilised people, or indeed by
any people, which I have found recorded, is that given by Garcilazo de la
Vega, a descendant of the Incas, as having been practised in Peru before the
country was subjugated by the Spaniards.[501] The Incas annually held great
hunts, when all the wild animals were driven from an immense circuit to a
central point. The beasts of prey were first destroyed as injurious. The wild
Guanacos and Vicunas were sheared; the old males and females killed, and
the others set at liberty. The various kinds of deer were examined; the old
males and females were likewise killed; "but the young females, with a
certain number of males, selected from the most beautiful and strong," were
given their freedom. Here, then, we have selection by man aiding natural
selection. So that the Incas followed exactly the reverse system of that
which our Scottish sportsmen are accused of following, namely, of steadily
killing the finest stags, thus causing the whole race to degenerate.[502] In

regard to the domesticated llamas and alpacas, they were separated in the
time of the Incas according to colour; and if by chance one in a flock was
born of the wrong colour, it was eventually put into another flock.
In the genus Auchenia there are four forms,—the Guanaco and Vicuna,
found wild and undoubtedly distinct species; the Llama and Alpaca, known
only in a domesticated condition. These four animals appear so different,
that most professed naturalists, especially those who have studied these
animals in their native country, maintain that they are specifically distinct,
notwithstanding that no one pretends to have seen a wild llama or alpaca.
Mr. Ledger, however, who has closely studied these animals both in Peru
and during their exportation to Australia, and who has made many
experiments on their propagation, adduces arguments[503] which seem to me
conclusive, that the llama is the domesticated descendant of the guanaco,
and the alpaca of the vicuna. And now that we know that these animals
many centuries ago were systematically bred and selected, there is nothing
surprising in the great amount of change which they have undergone.
It appeared to me at one time probable that, though ancient and semi-
civilised people might have attended to the improvement of their more
useful animals in essential points, yet that they would have disregarded
unimportant characters. But human nature is the same throughout the world:
fashion everywhere reigns supreme, and man is apt to value whatever he
may chance to possess. We have seen that in South America the niata cattle,
which certainly are not made useful by their shortened faces and upturned
nostrils, have been preserved. The Damaras of South Africa value their
cattle for uniformity of colour and enormously long horns. The Mongolians
value their yaks for their white tails. And I shall now show that there is
hardly any peculiarity in our most useful animals which, from fashion,
superstition, or some other motive, has not been valued, and consequently
preserved. With respect to cattle, "an early record," according to Youatt,[504]
"speaks of a hundred white cows with red ears being demanded as a
compensation by the princes of North and South Wales. If the cattle were of
a dark or black colour, 150 were to be presented." So that colour was
attended to in Wales before its subjugation by England. In Central Africa,
an ox that beats the ground with its tail is killed; and in South Africa some
of the Damaras will not eat the flesh of a spotted ox. The Kaffirs value an
animal with a musical voice; and "at a sale in British Kaffraria the low of a

heifer excited so much admiration that a sharp competition sprung up for
her possession, and she realised a considerable price."[505] With respect to
sheep, the Chinese prefer rams without horns; the Tartars prefer them with
spirally wound horns, because the hornless are thought to lose courage.[506]
Some of the Damaras will not eat the flesh of hornless sheep. In regard to
horses, at the end of the fifteenth century animals of the colour described as
liart pommé were most valued in France. The Arabs have a proverb, "Never
buy a horse with four white feet, for he carries his shroud with him;"[507]
the Arabs also, as we have seen, despise dun-coloured horses. So with dogs,
Xenophon and others at an ancient period were prejudiced in favour of
certain colours; and "white or slate-coloured hunting dogs were not
esteemed."[508]
Turning to poultry, the old Roman gourmands thought that the liver of a
white goose was the most savoury. In Paraguay black-skinned fowls are
kept because they are thought to be more productive, and their flesh the
most proper for invalids.[509] In Guiana, as I am informed by Sir R.
Schomburgk, the aborigines will not eat the flesh or eggs of the fowl, but
two races are kept distinct merely for ornament. In the Philippines, no less
than nine sub-varieties of the game cock are kept and named, so that they
must be separately bred.
At the present time in Europe, the smallest peculiarities are carefully
attended to in our most useful animals, either from fashion, or as a mark of
purity of blood. Many examples could be given, two will suffice. "In the
Western counties of England the prejudice against a white pig is nearly as
strong as against a black one in Yorkshire." In one of the Berkshire sub-
breeds, it is said, "the white should be confined to four white feet, a white
spot between the eyes, and a few white hairs behind each shoulder." Mr.
Saddler possessed "three hundred pigs, every one of which was marked in
this manner."[510] Marshall, towards the close of the last century, in
speaking of a change in one of the Yorkshire breeds of cattle, says the horns
have been considerably modified, as "a clean, small, sharp horn has been
fashionable for the last twenty years."[511] In a part of Germany the cattle of
the Race de Gfoehl are valued for many good qualities, but they must have
horns of a particular curvature and tint, so much so that mechanical means
are applied if they take a wrong direction; but the inhabitants "consider it of