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The Variation of Animals and Plants under Domestication by Charles Darwin

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plant, namely, pollen; for instance, I have seen the pollen-mass of an Ophrys,
which is a very complex structure, developed in the edge of an upper petal.
The segments of the calyx of the common pea have been observed partially
converted into carpels, including ovules, and with their tips converted into
stigmas. Mr. Salter and Dr. Maxwell Masters have found pollen within the
ovules of the passion-flower and of the rose. Buds may be developed in the
most unnatural positions, as on the petal of a flower. Numerous analogous
facts could be given. (27/68. Moquin-Tandon 'Teratologie Veg.' 1841 pages 218,
220, 353. For the case of the pea see 'Gardener's Chronicle' 1866 page 897.
With respect to pollen within ovules see Dr. Masters in 'Science Review'
October 1873 page 369. The Rev. J.M. Berkeley describes a bud developed on a
petal of a Clarkia in 'Gardener's Chronicle' April 28, 1866.)

I do not know how physiologists look at such facts as the foregoing. According
to the doctrine of pangenesis, the gemmules of the transposed organs become
developed in the wrong place, from uniting with wrong cells or aggregates of
cells during their nascent state; and this would follow from a slight
modification in their elective affinities. Nor ought we to feel much surprise
at the affinities of cells and gemmules varying, when we remember the many
curious cases given in the seventeenth chapter, of plants which absolutely
refuse to be fertilised by their own pollen, though abundantly fertile with
that of any other individual of the same species, and in some cases only with
that of a distinct species. It is manifest that the sexual elective affinities
of such plants--to use the term employed by Gartner--have been modified. As
the cells of adjoining or homologous parts will have nearly the same nature,
they will be particularly liable to acquire by variation each other's elective
affinities; and we can thus understand to a certain extent such cases as a
crowd of horns on the heads of certain sheep, of several spurs on the legs of
fowls, hackle-like feathers on the heads of the males of other fowls, and with
the pigeon wing-like feathers on their legs and membrane between their toes,
for the leg is the homologue of the wing. As all the organs of plants are
homologous and spring from a common axis, it is natural that they should be
eminently liable to transposition. It ought to be observed that when any
compound part, such as an additional limb or an antenna, springs from a false
position, it is only necessary that the few first gemmules should be wrongly
attached; for these whilst developing would attract other gemmules in due
succession, as in the regrowth of an amputated limb. When parts which are
homologous and similar in structure, as the vertebrae of snakes or the stamens
of polyandrous flowers, etc., are repeated many times in the same organism,
closely allied gemmules must be extremely numerous, as well as the points to
which they ought to become united; and, in accordance with the foregoing
views, we can to a certain extent understand Isid. Geoffroy Saint-Hilaire's
law, that parts, which are already multiple, are extremely liable to vary in

Variability often depends, as I have attempted to show, on the reproductive
organs being injuriously affected by changed conditions; and in this case the
gemmules derived from the various parts of the body are probably aggregated in
an irregular manner, some superfluous and others deficient. Whether a
superabundance of gemmules would lead to the increased size of any part cannot
be told; but we can see that their partial deficiency, without necessarily
leading to the entire abortion of the part, might cause considerable
modifications; for in the same manner as plants, if their own pollen be
excluded, are easily hybridised, so, in the case of cells, if the properly
succeeding gemmules were absent, they would probably combine easily with other
and allied gemmules, as we have just seen with transposed parts.

In variations caused by the direct action of changed conditions, of which
several instances have been given, certain parts of the body are directly
affected by the new conditions, and consequently throw off modified gemmules,
which are transmitted to the offspring. On any ordinary view it is
unintelligible how changed conditions, whether acting on the embryo, the young
or the adult, can cause inherited modifications. It is equally or even more
unintelligible on any ordinary view, how the effects of the long-continued use
or disuse of a part, or of changed habits of body or mind, can be inherited. A
more perplexing problem can hardly be proposed; but on our view we have only
to suppose that certain cells become at last structurally modified; and that
these throw off similarly modified gemmules. This may occur at any period of
development, and the modification will be inherited at a corresponding period;
for the modified gemmules will unite in all ordinary cases with the proper
preceding cells, and will consequently be developed at the same period at
which the modification first arose. With respect to mental habits or
instincts, we are so profoundly ignorant of the relation between the brain and
the power of thought that we do not know positively whether a fixed habit
induces any change in the nervous system, though this seems highly probable;
but when such habit or other mental attribute, or insanity, is inherited, we
must believe that some actual modification is transmitted (27/69. See some
remarks to this effect by Sir H. Holland in his 'Medical Notes' 1839 page
32.); and this implies, according to our hypothesis, that gemmules derived
from modified nerve-cells are transmitted to the offspring.

It is generally necessary that an organism should be exposed during several
generations to changed conditions or habits, in order that any modification
thus acquired should appear in the offspring. This may be partly due to the
changes not being at first marked enough to catch attention, but this
explanation is insufficient; and I can account for the fact only by the
assumption, which we shall see under the head of reversion is strongly
supported, that gemmules derived from each unmodified unit or part are
transmitted in large numbers to successive generations, and that the gemmules
derived from the same unit after it has been modified go on multiplying under
the same favourable conditions which first caused the modification, until at
last they become sufficiently numerous to overpower and supplant the old

A difficulty may be here noticed; we have seen that there is an important
difference in the frequency, though not in the nature, of the variations in
plants propagated by sexual and asexual generation. As far as variability
depends on the imperfect action of the reproductive organs under changed
conditions, we can at once see why plants propagated asexually should be far
less variable than those propagated sexually. With respect to the direct
action of changed conditions, we know that organisms produced from buds do not
pass through the earlier phases of development; they will therefore not be
exposed, at that period of life when structure is most readily modified, to
the various causes inducing variability in the same manner as are embryos and
young larval forms; but whether this is a sufficient explanation I know not.

With respect to variations due to reversion, there is a similar difference
between plants propagated from buds and seeds. Many varieties can be
propagated securely by buds, but generally or invariably revert to their
parent-forms by seed. So, also, hybridised plants can be multiplied to any
extent by buds, but are continually liable to reversion by seed,--that is, to
the loss of their hybrid or intermediate character. I can offer no
satisfactory explanation of these facts. Plants with variegated leaves,
phloxes with striped flowers, barberries with seedless fruit, can all be
securely propagated by buds taken from the stem or branches; but buds from the
roots of these plants almost invariably lose their character and revert to
their former condition. This latter fact is also inexplicable, unless buds
developed from the roots are as distinct from those on the stem, as is one bud
on the stem from another, and we know that these latter behave like
independent organisms.

Finally, we see that on the hypothesis of pangenesis variability depends on at
least two distinct groups of causes. Firstly, the deficiency, superabundance,
and transposition of gemmules, and the redevelopment of those which have long
been dormant; the gemmules themselves not having undergone any modification;
and such changes will amply account for much fluctuating variability.
Secondly, the direct action of changed conditions on the organisation, and of
the increased use or disuse of parts; and in this case the gemmules from the
modified units will be themselves modified, and, when sufficiently multiplied,
will supplant the old gemmules and be developed into new structures.

Turning now to the laws of Inheritance. If we suppose a homogeneous gelatinous
protozoon to vary and assume a reddish colour, a minute separated particle
would naturally, as it grew to full size, retain the same colour; and we
should have the simplest form of inheritance. (27/70. This is the view taken
by Prof. Hackel in his 'Generelle Morphologie' b. 2 s. 171, who says:
"Lediglich die partielle Identitat der specifisch constituirten Materie im
elterlichen und im kindlichen Organismus, die Theilung dieser Materie bei der
Fortpflanzung, ist die Ursache der Erblichkeit.") Precisely the same view may
be extended to the infinitely numerous and diversified units of which the
whole body of one of the higher animals is composed; the separated particles
being our gemmules. We have already sufficiently discussed by implication, the
important principle of inheritance at corresponding ages. Inheritance as
limited by sex and by the season of the year (for instance with animals
becoming white in winter) is intelligible if we may believe that the elective
affinities of the units of the body are slightly different in the two sexes,
especially at maturity, and in one or both sexes at different seasons, so that
they unite with different gemmules. It should be remembered that, in the
discussion on the abnormal transposition of organs, we have seen reason to
believe that such elective affinities are readily modified. But I shall soon
have to recur to sexual and seasonal inheritance. These several laws are
therefore explicable to a large extent through pangenesis, and on no other
hypothesis which has as yet been advanced.

But it appears at first sight a fatal objection to our hypothesis that a part
or organ may be removed during several successive generations, and if the
operation be not followed by disease, the lost part reappears in the
offspring. Dogs and horses formerly had their tails docked during many
generations without any inherited effect; although, as we have seen, there is
some reason to believe that the tailless condition of certain sheep-dogs is
due to such inheritance. Circumcision has been practised by the Jews from a
remote period, and in most cases the effects of the operation are not visible
in the offspring; though some maintain that an inherited effect does
occasionally appear. If inheritance depends on the presence of disseminated
gemmules derived from all the units of the body, why does not the amputation
or mutilation of a part, especially if effected on both sexes, invariably
affect the offspring? The answer in accordance with our hypothesis probably is
that gemmules multiply and are transmitted during a long series of
generations--as we see in the reappearance of zebrine stripes on the horse--in
the reappearance of muscles and other structures in man which are proper to
his lowly organised progenitors, and in many other such cases. Therefore the
long-continued inheritance of a part which has been removed during many
generations is no real anomaly, for gemmules formerly derived from the part
are multiplied and transmitted from generation to generation.

We have as yet spoken only of the removal of parts, when not followed by
morbid action: but when the operation is thus followed, it is certain that the
deficiency is sometimes inherited. In a former chapter instances were given,
as of a cow, the loss of whose horn was followed by suppuration, and her
calves were destitute of a horn on the same side of their heads. But the
evidence which admits of no doubt is that given by Brown-Sequard with respect
to guinea-pigs, which after their sciatic nerves had been divided, gnawed off
their own gangrenous toes, and the toes of their offspring were deficient in
at least thirteen instances on the corresponding feet. The inheritance of the
lost part in several of these cases is all the more remarkable as only one
parent was affected; but we know that a congenital deficiency is often
transmitted from one parent alone--for instance, the offspring of hornless
cattle of either sex, when crossed with perfect animals, are often hornless.
How, then, in accordance with our hypothesis can we account for mutilations
being sometimes strongly inherited, if they are followed by diseased action?
The answer probably is that all the gemmules of the mutilated or amputated
part are gradually attracted to the diseased surface during the reparative
process, and are there destroyed by the morbid action.

A few words must be added on the complete abortion of organs. When a part
becomes diminished by disuse prolonged during many generations, the principle
of economy of growth, together with intercrossing, will tend to reduce it
still further as previously explained, but this will not account for the
complete or almost complete obliteration of, for instance, a minute papilla of
cellular tissue representing a pistil, or of a microscopically minute nodule
of bone representing a tooth. In certain cases of suppression not yet
completed, in which a rudiment occasionally reappears through reversion,
dispersed gemmules derived from this part must, according to our view, still
exist; we must therefore suppose that the cells, in union with which the
rudiment was formerly developed, fail in their affinity for such gemmules,
except in the occasional cases of reversion. But when the abortion is complete
and final, the gemmules themselves no doubt perish; nor is this in any way
improbable, for, though a vast number of active and long-dormant gemmules are
nourished in each living creature, yet there must be some limit to their
number; and it appears natural that gemmules derived from reduced and useless
parts would be more liable to perish than those freshly derived from other
parts which are still in full functional activity.

The last subject that need be discussed, namely, Reversion, rests on the
principle that transmission and development, though generally acting in
conjunction, are distinct powers; and the transmission of gemmules with their
subsequent development shows us how this is possible. We plainly see the
distinction in the many cases in which a grandfather transmits to his
grandson, through his daughter, characters which she does not, or cannot,
possess. But before proceeding, it will be advisable to say a few words about
latent or dormant characters. Most, or perhaps all, of the secondary
characters, which appertain to one sex, lie dormant in the other sex; that is,
gemmules capable of development into the secondary male sexual characters are
included within the female; and conversely female characters in the male: we
have evidence of this in certain masculine characters, both corporeal and
mental, appearing in the female, when her ovaria are diseased or when they
fail to act from old age. In like manner female characters appear in castrated
males, as in the shape of the horns of the ox, and in the absence of horns in
castrated stags. Even a slight change in the conditions of life due to
confinement sometimes suffices to prevent the development of masculine
characters in male animals, although their reproductive organs are not
permanently injured. In the many cases in which masculine characters are
periodically renewed, these are latent at other seasons; inheritance as
limited by sex and season being here combined. Again, masculine characters
generally lie dormant in male animals until they arrive at the proper age for
reproduction. The curious case formerly given of a Hen which assumed the
masculine characters, not of her own breed but of a remote progenitor,
illustrates the close connection between latent sexual characters and ordinary

With those animals and plants which habitually produce several forms, as with
certain butterflies described by Mr. Wallace, in which three female forms and
one male form co-exist, or, as with the trimorphic species of Lythrum and
Oxalis, gemmules capable of reproducing these different forms must be latent
in each individual.

Insects are occasionally produced with one side or one quarter of their bodies
like that of the male, with the other half or three-quarters like that of the
female. In such cases the two sides are sometimes wonderfully different in
structure, and are separated from each other by a sharp line. As gemmules
derived from every part are present in each individual of both sexes, it must
be the elective affinities of the nascent cells which in these cases differ
abnormally on the two sides of the body. Almost the same principle comes into
play with those animals, for instance, certain gasteropods and Verruca amongst
cirripedes, which normally have the two sides of the body constructed on a
very different plan; and yet a nearly equal number of individuals have either
side modified in the same remarkable manner.

Reversion, in the ordinary sense of the word, acts so incessantly, that it
evidently forms an essential part of the general law of inheritance. It occurs
with beings, however propagated, whether by buds or seminal generation, and
sometimes may be observed with advancing age even in the same individual. The
tendency to reversion is often induced by a change of conditions, and in the
plainest manner by crossing. Crossed forms of the first generation are
generally nearly intermediate in character between their two parents; but in
the next generation the offspring commonly revert to one or both of their
grandparents, and occasionally to more remote ancestors. How can we account
for these facts? Each unit in a hybrid must throw off, according to the
doctrine of pangenesis, an abundance of hybridised gemmules, for crossed
plants can be readily and largely propagated by buds; but by the same
hypothesis dormant gemmules derived from both pure parent-forms are likewise
present; and as these gemmules retain their normal condition, they would, it
is probable, be enabled to multiply largely during the lifetime of each
hybrid. Consequently the sexual elements of a hybrid will include both pure
and hybridised gemmules; and when two hybrids pair, the combination of pure
gemmules derived from the one hybrid with the pure gemmules of the same parts
derived from the other, would necessarily lead to complete reversion of
character; and it is, perhaps, not too bold a supposition that unmodified and
undeteriorated gemmules of the same nature would be especially apt to combine.
Pure gemmules in combination with hybridised gemmules would lead to partial
reversion. And lastly, hybridised gemmules derived from both parent-hybrids
would simply reproduce the original hybrid form. (27/71. In these remarks I,
in fact, follow Naudin, who speaks of the elements or essences of the two
species which are crossed. See his excellent memoir in the 'Nouvelles Archives
du Museum' tome 1 page 151.) All these cases and degrees of reversion
incessantly occur.

It was shown in the fifteenth chapter that certain characters are antagonistic
to each other or do not readily blend; hence, when two animals with
antagonistic characters are crossed, it might well happen that a sufficiency
of gemmules in the male alone for the reproduction of his peculiar characters,
and in the female alone for the reproduction of her peculiar characters, would
not be present; and in this case dormant gemmules derived from the same part
in some remote progenitor might easily gain the ascendancy, and cause the
reappearance of the long-lost character. For instance, when black and white
pigeons, or black and white fowls, are crossed,--colours which do not readily
blend,--blue plumage in the one case, evidently derived from the rock-pigeon,
and red plumage in the other case, derived from the wild jungle-cock,
occasionally reappear. With uncrossed breeds the same result follows, under
conditions which favour the multiplication and development of certain dormant
gemmules, as when animals become feral and revert to their pristine character.
A certain number of gemmules being requisite for the development of each
character, as is known to be the case from several spermatozoa or pollen-
grains being necessary for fertilisation, and time favouring their
multiplication, will perhaps account for the curious cases, insisted on by Mr.
Sedgwick, of certain diseases which regularly appear in alternate generations.
This likewise holds good, more or less strictly, with other weakly inherited
modifications. Hence, as I have heard it remarked, certain diseases appear to
gain strength by the intermission of a generation. The transmission of dormant
gemmules during many successive generations is hardly in itself more
improbable, as previously remarked, than the retention during many ages of
rudimentary organs, or even only of a tendency to the production of a
rudiment; but there is no reason to suppose that dormant gemmules can be
transmitted and propagated for ever. Excessively minute and numerous as they
are believed to be, an infinite number derived, during a long course of
modification and descent, from each unit of each progenitor, could not be
supported or nourished by the organism. But it does not seem improbable that
certain gemmules, under favourable conditions, should be retained and go on
multiplying for a much longer period than others. Finally, on the view here
given, we certainly gain some insight into the wonderful fact that the child
may depart from the type of both its parents, and resemble its grandparents,
or ancestors removed by many hundreds of generations.


The hypothesis of Pangenesis, as applied to the several great classes of facts
just discussed, no doubt is extremely complex, but so are the facts. The chief
assumption is that all the units of the body, besides having the universally
admitted power of growing by self-division, throw off minute gemmules which
are dispersed through the system. Nor can this assumption be considered as too
bold, for we know from the cases of graft-hybridisation that formative matter
of some kind is present in the tissues of plants, which is capable of
combining with that included in another individual, and of reproducing every
unit of the whole organism. But we have further to assume that the gemmules
grow, multiply, and aggregate themselves into buds and the sexual elements;
their development depending on their union with other nascent cells or units.
They are also believed to be capable of transmission in a dormant state, like
seeds in the ground, to successive generations.

In a highly-organised animal, the gemmules thrown off from each different unit
throughout the body must be inconceivably numerous and minute. Each unit of
each part, as it changes during development, and we know that some insects
undergo at least twenty metamorphoses, must throw off its gemmules. But the
same cells may long continue to increase by self-division, and even become
modified by absorbing peculiar nutriment, without necessarily throwing off
modified gemmules. All organic beings, moreover, include many dormant gemmules
derived from their grandparents and more remote progenitors, but not from all
their progenitors. These almost infinitely numerous and minute gemmules are
contained within each bud, ovule, spermatozoon, and pollen-grain. Such an
admission will be declared impossible; but number and size are only relative
difficulties. Independent organisms exist which are barely visible under the
highest powers of the microscope, and their germs must be excessively minute.
Particles of infectious matter, so small as to be wafted by the wind or to
adhere to smooth paper, will multiply so rapidly as to infect within a short
time the whole body of a large animal. We should also reflect on the admitted
number and minuteness of the molecules composing a particle of ordinary
matter. The difficulty, therefore, which at first appears insurmountable, of
believing in the existence of gemmules so numerous and small as they must be
according to our hypothesis, has no great weight.

The units of the body are generally admitted by physiologists to be
autonomous. I go one step further and assume that they throw off reproductive
gemmules. Thus an organism does not generate its kind as a whole, but each
separate unit generates its kind. It has often been said by naturalists that
each cell of a plant has the potential capacity of reproducing the whole
plant; but it has this power only in virtue of containing gemmules derived
from every part. When a cell or unit is from some cause modified, the gemmules
derived from it will be in like manner modified. If our hypothesis be
provisionally accepted, we must look at all the forms of asexual reproduction,
whether occurring at maturity or during youth, as fundamentally the same, and
dependent on the mutual aggregation and multiplication of the gemmules. The
regrowth of an amputated limb and the healing of a wound is the same process
partially carried out. Buds apparently include nascent cells, belonging to
that stage of development at which the budding occurs, and these cells are
ready to unite with the gemmules derived from the next succeeding cells. The
sexual elements, on the other hand, do not include such nascent cells; and the
male and female elements taken separately do not contain a sufficient number
of gemmules for independent development, except in the cases of
parthenogenesis. The development of each being, including all the forms of
metamorphosis and metagenesis, depends on the presence of gemmules thrown off
at each period of life, and on their development, at a corresponding period,
in union with preceding cells. Such cells may be said to be fertilised by the
gemmules which come next in due order of development. Thus the act of ordinary
impregnation and the development of each part in each being are closely
analogous processes. The child, strictly speaking, does not grow into the man,
but includes germs which slowly and successively become developed and form the
man. In the child, as well as in the adult, each part generates the same part.
Inheritance must be looked at as merely a form of growth, like the self-
division of a lowly-organised unicellular organism. Reversion depends on the
transmission from the forefather to his descendants of dormant gemmules, which
occasionally become developed under certain known or unknown conditions. Each
animal and plant may be compared with a bed of soil full of seeds, some of
which soon germinate, some lie dormant for a period, whilst others perish.
When we hear it said that a man carries in his constitution the seeds of an
inherited disease, there is much truth in the expression. No other attempt, as
far as I am aware, has been made, imperfect as this confessedly is, to connect
under one point of view these several grand classes of facts. An organic being
is a microcosm--a little universe, formed of a host of self-propagating
organisms, inconceivably minute and numerous as the stars in heaven.




As summaries have been added to nearly all the chapters, and as, in the
chapter on pangenesis, various subjects, such as the forms of reproduction,
inheritance, reversion, the causes and laws of variability, etc., have been
recently discussed, I will here only make a few general remarks on the more
important conclusions which may be deduced from the multifarious details given
throughout this work.

Savages in all parts of the world easily succeed in taming wild animals; and
those inhabiting any country or island, when first visited by man, would
probably have been still more easily tamed. Complete subjugation generally
depends on an animal being social in its habits, and on receiving man as the
chief of the herd or family. In order that an animal should be domesticated it
must be fertile under changed conditions of life, and this is far from being
always the case. An animal would not have been worth the labour of
domestication, at least during early times, unless of service to man. From
these circumstances the number of domesticated animals has never been large.
With respect to plants, I have shown in the ninth chapter how their varied
uses were probably first discovered, and the early steps in their cultivation.
Man could not have known, when he first domesticated an animal or plant,
whether it would flourish and multiply when transported to other countries,
therefore he could not have been thus influenced in his choice. We see that
the close adaptation of the reindeer and camel to extremely cold and hot
countries has not prevented their domestication. Still less could man have
foreseen whether his animals and plants would vary in succeeding generations
and thus give birth to new races; and the small capacity of variability in the
goose has not prevented its domestication from a remote epoch.

With extremely few exceptions, all animals and plants which have been long
domesticated have varied greatly. It matters not under what climate, or for
what purpose they are kept, whether as food for man or beast, for draught or
hunting, for clothing or mere pleasure,--under all these circumstances races
have been produced which differ more from one another than do the forms which
in a state of nature are ranked as different species. Why certain animals and
plants have varied more under domestication than others we do not know, any
more than why some are rendered more sterile than others under changed
conditions of life. But we have to judge of the amount of variation which our
domestic productions have undergone, chiefly by the number and amount of
difference between the races which have been formed, and we can often clearly
see why many and distinct races have not been formed, namely, because slight
successive variations have not been steadily accumulated; and such variations
will never be accumulated if an animal or plant be not closely observed, much
valued, and kept in large numbers.

The fluctuating, and, as far as we can judge, never-ending variability of our
domesticated productions,--the plasticity of almost their whole organisation,-
-is one of the most important lessons which we learn from the numerous details
given in the earlier chapters of this work. Yet domesticated animals and
plants can hardly have been exposed to greater changes in their conditions of
life than have many natural species during the incessant geological,
geographical, and climatal changes to which the world has been subject; but
domesticated productions will often have been exposed to more sudden changes
and to less continuously uniform conditions. As man has domesticated so many
animals and plants belonging to widely different classes, and as he certainly
did not choose with prophetic instinct those species which would vary most, we
may infer that all natural species, if exposed to analogous conditions, would,
on an average, vary to the same degree. Few men at the present day will
maintain that animals and plants were created with a tendency to vary, which
long remained dormant, in order that fanciers in after ages might rear, for
instance, curious breeds of the fowl, pigeon, or canary-bird.

From several causes it is difficult to judge of the amount of modification
which our domestic productions have undergone. In some cases the primitive
parent-stock has become extinct; or it cannot be recognised with certainty,
owing to its supposed descendants having been so much modified. In other cases
two or more closely-allied forms, after being domesticated, have crossed; and
then it is difficult to estimate how much of the character of the present
descendants ought to be attributed to variation, and how much to the influence
of the several parent-stocks. But the degree to which our domesticated breeds
have been modified by the crossing of distinct species has probably been much
exaggerated by some authors. A few individuals of one form would seldom
permanently affect another form existing in greater numbers; for, without
careful selection, the stain of the foreign blood would soon be obliterated,
and during early and barbarous times, when our animals were first
domesticated, such care would seldom have been taken.

There is good reason to believe in the case of the dog, ox, pig, and of some
other animals, that several of our races are descended from distinct wild
prototypes; nevertheless the belief in the multiple origin of our domesticated
animals has been extended by some few naturalists and by many breeders to an
unauthorised extent. Breeders refuse to look at the whole subject under a
single point of view; I have heard it said by a man, who maintained that our
fowls were descended from at least half-a-dozen aboriginal species, that the
evidence of the common origin of pigeons, ducks and rabbits, was of no avail
with respect to fowls. Breeders overlook the improbability of many species
having been domesticated at an early and barbarous period. They do not
consider the improbability of species having existed in a state of nature
which, if they resembled our present domestic breeds, would have been highly
abnormal in comparison with all their congeners. They maintain that certain
species, which formerly existed, have become extinct, or are now unknown,
although formerly known. The assumption of so much recent extinction is no
difficulty in their eyes; for they do not judge of its probability by the
facility or difficulty of the extinction of other closely-allied wild forms.
Lastly, they often ignore the whole subject of geographical distribution as
completely as if it were the result of chance.

Although from the reasons just assigned it is often difficult to judge
accurately of the amount of change which our domesticated productions have
undergone, yet this can be ascertained in the cases in which all the breeds
are known to be descended from a single species,--as with the pigeon, duck,
rabbit, and almost certainly with the fowl; and by the aid of analogy this can
be judged of to a certain extent with domesticated animals descended from
several wild stocks. It is impossible to read the details given in the earlier
chapters and in many published works, or to visit our various exhibitions,
without being deeply impressed with the extreme variability of our
domesticated animals and cultivated plants. No part of the organisation
escapes the tendency to vary. The variations generally affect parts of small
vital or physiological importance, but so it is with the differences which
exist between closely-allied species. In these unimportant characters there is
often a greater difference between the breeds of the same species than between
the natural species of the same genus, as Isidore Geoffroy has shown to be the
case with size, and as is often the case with the colour, texture, form, etc.,
of the hair, feathers, horns, and other dermal appendages.

It has often been asserted that important parts never vary under
domestication, but this is a complete error. Look at the skull of the pig in
any one of the highly improved breeds, with the occipital condyles and other
parts greatly modified; or look at that of the niata ox. Or, again, in the
several breeds of the rabbit, observe the elongated skull, with the
differently shaped occipital foramen, atlas, and other cervical vertebrae. The
whole shape of the brain, together with the skull, has been modified in Polish
fowls; in other breeds of the fowl the number of the vertebrae and the forms
of the cervical vertebrae have been changed. In certain pigeons the shape of
the lower jaw, the relative length of the tongue, the size of the nostrils and
eyelids, the number and shape of the ribs, the form and size of the
oesophagus, have all varied. In certain quadrupeds the length of the
intestines has been much increased or diminished. With plants we see wonderful
differences in the stones of various fruits. In the Cucurbitaceae several
highly important characters have varied, such as the sessile position of the
stigmas on the ovarium, the position of the carpels, and the projection of the
ovarium out of the receptacle. But it would be useless to run through the many
facts given in the earlier chapters.

It is notorious how greatly the mental disposition, tastes, habits, consensual
movements, loquacity or silence, and tone of voice have varied and been
inherited in our domesticated animals. The dog offers the most striking
instance of changed mental attributes, and these differences cannot be
accounted for by descent from distinct wild types.

New characters may appear and old ones disappear at any stage of development,
being inherited at a corresponding stage. We see this in the difference
between the eggs, the down on the chickens and the first plumage of the
various breeds of the fowl; and still more plainly in the differences between
the caterpillars and cocoons of the various breeds of the silk-moth. These
facts, simple as they appear, throw light on the differences between the
larval and adult states of allied natural species, and on the whole great
subject of embryology. New characters first appearing late in life are apt to
become attached exclusively to that sex in which they first arose, or they may
be developed in a much higher degree in this than in the other sex; or again,
after having become attached to one sex, they may be transferred to the
opposite sex. These facts, and more especially the circumstance that new
characters seem to be particularly liable, from some unknown cause, to become
attached to the male sex, have an important bearing on the acquirement of
secondary sexual characters by animals in a state of nature.

It has sometimes been said that our domestic races do not differ in
constitutional peculiarities, but this cannot be maintained. In our improved
cattle, pigs, etc., the period of maturity, including that of the second
dentition, has been much hastened. The period of gestation varies much, and
has been modified in a fixed manner in one or two cases. In some breeds of
poultry and pigeons the period at which the down and the first plumage are
acquired, differs. The number of moults through which the larvae of silk-moths
pass, varies. The tendency to fatten, to yield much milk, to produce many
young or eggs at a birth or during life, differs in different breeds. We find
different degrees of adaptation to climate, and different tendencies to
certain diseases, to the attacks of parasites, and to the action of certain
vegetable poisons. With plants, adaptation to certain soils, the power of
resisting frost, the period of flowering and fruiting, the duration of life,
the period of shedding the leaves or of retaining them throughout the winter,
the proportion and nature of certain chemical compounds in the tissues or
seeds, all vary.

There is, however, one important constitutional difference between domestic
races and species; I refer to the sterility which almost invariably follows,
in a greater or less degree, when species are crossed, and to the perfect
fertility of the most distinct domestic races, with the exception of a very
few plants, when similarly crossed. It is certainly a most remarkable fact
that many closely-allied species, which in appearance differ extremely little,
should yield when crossed only a few more or less sterile offspring, or none
at all; whilst domestic races which differ conspicuously from each other are,
when united, remarkably fertile, and yield perfectly fertile offspring. But
this fact is not in reality so inexplicable as it at first appears. In the
first place, it was clearly shown in the nineteenth chapter that the sterility
of crossed species does not depend chiefly on differences in their external
structure or general constitution, but on differences in the reproductive
system, analogous to those which cause the lessened fertility of the
illegitimate unions of dimorphic and trimorphic plants. In the second place,
the Pallasian doctrine, that species after having been long domesticated lose
their natural tendency to sterility when crossed, has been shown to be highly
probable or almost certain. We cannot avoid this conclusion when we reflect on
the parentage and present fertility of the several breeds of the dog, of the
Indian or humped and European cattle, and of the two chief kinds of pigs.
Hence it would be unreasonable to expect that races formed under domestication
should acquire sterility when crossed, whilst at the same time we admit that
domestication eliminates the normal sterility of crossed species. Why with
closely-allied species their reproductive systems should almost invariably
have been modified in so peculiar a manner as to be mutually incapable of
acting on each other--though in unequal degrees in the two sexes, as shown by
the difference in fertility between reciprocal crosses of the same species--we
do not know, but may with much probability infer the cause to be as follows.
Most natural species have been habituated to nearly uniform conditions of life
for an incomparably longer time than have domestic races; and we positively
know that changed conditions exert an especial and powerful influence on the
reproductive system. Hence this difference may well account for the difference
in the power of reproduction between domestic races when crossed and species
when crossed. It is probably in chief part owing to the same cause that
domestic races can be suddenly transported from one climate to another, or
placed under widely different conditions, and yet retain in most cases their
fertility unimpaired; whilst a multitude of species subjected to lesser
changes are rendered incapable of breeding.

The offspring of crossed domestic races and of crossed species resemble each
other in most respects, with the one important exception of fertility; they
often partake in the same unequal degree of the characters of their parents,
one of which is often prepotent over the other; and they are liable to
reversion of the same kind. By successive crosses one species may be made to
absorb completely another, and so it notoriously is with races. The latter
resemble species in many other ways. They sometimes inherit their newly-
acquired characters almost or even quite as firmly as species. The conditions
leading to variability and the laws governing its nature appear to be the same
in both. Varieties can be classed in groups under groups, like species under
genera, and these under families and orders; and the classification may be
either artificial,--that is, founded on any arbitrary character,--or natural.
With varieties a natural classification is certainly founded, and with species
is apparently founded, on community of descent, together with the amount of
modification which the forms have undergone. The characters by which domestic
varieties differ from one another are more variable than those distinguishing
species, though hardly more so than with certain polymorphic species; but this
greater degree of variability is not surprising, as varieties have generally
been exposed within recent times to fluctuating conditions of life, and are
much more liable to have been crossed; they are also in many cases still
undergoing, or have recently undergone, modification by man's methodical or
unconscious selection.

Domestic varieties as a general rule certainly differ from one another in less
important parts than do species; and when important differences occur, they
are seldom firmly fixed; but this fact is intelligible, if we consider man's
method of selection. In the living animal or plant he cannot observe internal
modifications in the more important organs; nor does he regard them as long as
they are compatible with health and life. What does the breeder care about any
slight change in the molar teeth of his pigs, or for an additional molar tooth
in the dog; or for any change in the intestinal canal or other internal organ?
The breeder cares for the flesh of his cattle being well marbled with fat, and
for an accumulation of fat within the abdomen of his sheep, and this he has
effected. What would the floriculturist care for any change in the structure
of the ovarium or of the ovules? As important internal organs are certainly
liable to numerous slight variations, and as these would probably be
transmitted, for many strange monstrosities are inherited, man could
undoubtedly effect a certain amount of change in these organs. When he has
produced any modification in an important part, he has generally done so
unintentionally, in correlation with some other conspicuous part. For
instance, he has given ridges and protuberances to the skulls of fowls, by
attending to the form of the comb, or to the plume of feathers on the head. By
attending to the external form of the pouter-pigeon, he has enormously
increased the size of the oesophagus, and has added to the number of the ribs,
and given them greater breadth. With the carrier-pigeon, by increasing through
steady selection the wattles on the upper mandible, he has greatly modified
the form of the lower mandible; and so in many other cases. Natural species,
on the other hand, have been modified exclusively for their own good, to fit
them for infinitely diversified conditions of life, to avoid enemies of all
kinds, and to struggle against a host of competitors. Hence, under such
complex conditions, it would often happen that modifications of the most
varied kinds, in important as well as in unimportant parts, would be
advantageous or even necessary; and they would slowly but surely be acquired
through the survival of the fittest. Still more important is the fact that
various indirect modifications would likewise arise through the law of
correlated variation.

Domestic breeds often have an abnormal or semi-monstrous character, as amongst
dogs, the Italian greyhound, bulldog, Blenheim spaniel, and bloodhound,--some
breeds of cattle and pigs,--several breeds of the fowl,--and the chief breeds
of the pigeon. In such abnormal breeds, parts which differ but slightly or not
at all in the allied natural species, have been greatly modified. This may be
accounted for by man's often selecting, especially at first, conspicuous and
semi-monstrous deviations of structure. We should, however, be cautious in
deciding what deviations ought to be called monstrous: there can hardly be a
doubt that, if the brush of horse-like hair on the breast of the turkey-cock
had first appeared in the domesticated bird, it would have been considered as
a monstrosity; the great plume of feathers on the head of the Polish cock has
been thus designated, though plumes are common on the heads of many kinds of
birds; we might call the wattle or corrugated skin round the base of the beak
of the English carrier-pigeon a monstrosity, but we do not thus speak of the
globular fleshy excrescence at the base of the beak of the Carpophaga

Some authors have drawn a wide distinction between artificial and natural
breeds; although in extreme cases the distinction is plain, in many other
cases it is arbitrary; the difference depending chiefly on the kind of
selection which has been applied. Artificial breeds are those which have been
intentionally improved by man; they frequently have an unnatural appearance,
and are especially liable to lose their characters through reversion and
continued variability. The so-called natural breeds, on the other hand, are
those which are found in semi-civilised countries, and which formerly
inhabited separate districts in nearly all the European kingdoms. They have
been rarely acted on by man's intentional selection; more frequently by
unconscious selection, and partly by natural selection, for animals kept in
semi-civilised countries have to provide largely for their own wants. Such
natural breeds will also have been directly acted on by the differences,
though slight, in the surrounding conditions.

There is a much more important distinction between our several breeds, namely,
in some having originated from a strongly-marked or semi-monstrous deviation
of structure, which, however, may subsequently have been augmented by
selection; whilst others have been formed in so slow and insensible a manner,
that if we could see their early progenitors we should hardly be able to say
when or how the breed first arose. From the history of the racehorse,
greyhound, gamecock, etc., and from their general appearance, we may feel
nearly confident that they were formed by a slow process of improvement; and
we know that this has been the case with the carrier-pigeon, as well as with
some other pigeons. On the other hand, it is certain that the ancon and
mauchamp breeds of sheep, and almost certain that the niata cattle, turnspit,
and pug-dogs, jumper and frizzled fowls, short-faced tumbler pigeons, hook-
billed ducks, etc., suddenly appeared in nearly the same state as we now see
them. So it has been with many cultivated plants. The frequency of these cases
is likely to lead to the false belief that natural species have often
originated in the same abrupt manner. But we have no evidence of the
appearance, or at least of the continued procreation, under nature, of abrupt
modifications of structure; and various general reasons could be assigned
against such a belief.

On the other hand, we have abundant evidence of the constant occurrence under
nature of slight individual differences of the most diversified kinds; and we
are thus led to conclude that species have generally originated by the natural
selection of extremely slight differences. This process may be strictly
compared with the slow and gradual improvement of the racehorse, greyhound,
and gamecock. As every detail of structure in each species has to be closely
adapted to its habits of life, it will rarely happen that one part alone will
be modified; but, as was formerly shown, the co-adapted modifications need not
be absolutely simultaneous. Many variations, however, are from the first
connected by the law of correlation. Hence it follows that even closely-allied
species rarely or never differ from one another by one character alone; and
the same remark is to a certain extent applicable to domestic races; for
these, if they differ much, generally differ in many respects.

Some naturalists boldly insist (28/1. Godron 'De l'Espece' 1859 tome 2 page 44
etc.) that species are absolutely distinct productions, never passing by
intermediate links into one another; whilst they maintain that domestic
varieties can always be connected either with one another or with their
parent-forms. But if we could always find the links between the several breeds
of the dog, horse, cattle, sheep, pigs, etc., there would not have been such
incessant doubts whether they were descended from one or several species. The
greyhound genus, if such a term may be used, cannot be closely connected with
any other breed, unless, perhaps, we go back to the ancient Egyptian
monuments. Our English bulldog also forms a very distinct breed. In all these
cases crossed breeds must of course be excluded, for distinct natural species
can thus be likewise connected. By what links can the Cochin fowl be closely
united with others? By searching for breeds still preserved in distant lands,
and by going back to historical records, tumbler-pigeons, carriers, and barbs
can be closely connected with the parent rock-pigeon; but we cannot thus
connect the turbit or the pouter. The degree of distinctness between the
various domestic breeds depends on the amount of modification which they have
undergone, and more especially on the neglect and final extinction of
intermediate and less-valued forms.

It has often been argued that no light is thrown on the changes which natural
species are believed to undergo from the admitted changes of domestic races,
as the latter are said to be mere temporary productions, always reverting, as
soon as they become feral, to their pristine form. This argument has been well
combated by Mr. Wallace (28/2. 'Journal Proc. Linn. Soc.' 1858 volume 3 page
60.) and full details were given in the thirteenth chapter, showing that the
tendency to reversion in feral animals and plants has been greatly
exaggerated, though no doubt it exists to a certain extent. It would be
opposed to all the principles inculcated in this work, if domestic animals,
when exposed to new conditions and compelled to struggle for their own wants
against a host of foreign competitors, were not modified in the course of
time. It should also be remembered that many characters lie latent in all
organic beings, ready to be evolved under fitting conditions; and in breeds
modified within recent times, the tendency to reversion is particularly
strong. But the antiquity of some of our breeds clearly proves that they
remain nearly constant as long as their conditions of life remain the same.

It has been boldly maintained by some authors that the amount of variation to
which our domestic productions are liable is strictly limited; but this is an
assertion resting on little evidence. Whether or not the amount of change in
any particular direction is limited, the tendency to general variability is,
as far as we can judge, unlimited. Cattle, sheep, and pigs have varied under
domestication from the remotest period, as shown by the researches of
Rutimeyer and others; yet these animals have been improved to an unparalleled
degree, within quite recent times, and this implies continued variability of
structure. Wheat, as we know from the remains found in the Swiss lake-
dwellings, is one of the most anciently cultivated plants, yet at the present
day new and better varieties frequently arise. It may be that an ox will never
be produced of larger size and finer proportions, or a racehorse fleeter, than
our present animals, or a gooseberry larger than the London variety; but he
would be a bold man who would assert that the extreme limit in these respects
has been finally attained. With flowers and fruit it has repeatedly been
asserted that perfection has been reached, but the standard has soon been
excelled. A breed of pigeons may never be produced with a beak shorter than
that of the present short-faced tumbler, or with one longer than that of the
English carrier, for these birds have weak constitutions and are bad breeders;
but shortness and length of beak are the points which have been steadily
improved during the last 150 years, and some of the best judges deny that the
goal has yet been reached. From reasons which could be assigned, it is
probable that parts which have now reached their maximum development, might,
after remaining constant during a long period, vary again in the direction of
increase under new conditions of life. But there must be, as Mr. Wallace has
remarked with much truth (28/3. 'The Quarterly Journal of Science' October
1867 page 486.), a limit to change in certain directions both with natural and
domestic productions; for instance, there must be a limit to the fleetness of
any terrestrial animal, as this will be determined by the friction to be
overcome, the weight to be carried, and the power of contraction in the
muscular fibres. The English racehorse may have reached this limit; but it
already surpasses in fleetness its own wild progenitor and all other equine
species. The short-faced tumbler-pigeon has a beak shorter, and the carrier a
beak longer, relatively to the size of their bodies, than that of any natural
species of the family. Our apples, pears and gooseberries bear larger fruit
than those of any natural species of the same genera; and so in many other

It is not surprising, seeing the great difference between many domestic
breeds, that some few naturalists have concluded that each is descended from a
distinct aboriginal stock, more especially as the principle of selection has
been ignored, and the high antiquity of man, as a breeder of animals, has only
recently become known. Most naturalists, however, freely admit that our
various breeds, however dissimilar, are descended from a single stock,
although they do not know much about the art of breeding, cannot show the
connecting links, nor say where and when the breeds arose. Yet these same
naturalists declare, with an air of philosophical caution, that they will
never admit that one natural species has given birth to another until they
behold all the transitional steps. Fanciers use exactly the same language with
respect to domestic breeds; thus, an author of an excellent treatise on
pigeons says he will never allow that the carrier and fantail are the
descendants of the wild rock-pigeon, until the transitions have "actually been
observed, and can be repeated whenever man chooses to set about the task." No
doubt it is difficult to realise that slight changes added up during long
centuries can produce such great results; but he who wishes to understand the
origin of domestic breeds or of natural species must overcome this difficulty.

The causes which excite and the laws which govern variability have been
discussed so lately, that I need here only enumerate the leading points. As
domesticated organisms are much more liable to slight deviations of structure
and to monstrosities than species living under their natural conditions, and
as widely-ranging species generally vary more than those which inhabit
restricted areas, we may infer that variability mainly depends on changed
conditions of life. We must not overlook the effects of the unequal
combination of the characters derived from both parents, or reversion to
former progenitors. Changed conditions have an especial tendency to render the
reproductive organs more or less impotent, as shown in the chapter devoted to
this subject; and these organs consequently often fail to transmit faithfully
the parental characters. Changed conditions also act directly and definitely
on the organisation, so that all or nearly all the individuals of the same
species thus exposed become modified in the same manner; but why this or that
part is especially affected we can seldom or ever say. In most cases, however,
a change in the conditions seems to act indefinitely, causing diversified
variations in nearly the same manner as exposure to cold or the absorption of
the same poison affects different individuals in different ways. We have
reason to suspect that an habitual excess of highly-nutritious food, or an
excess relatively to the wear and tear of the organisation from exercise, is a
powerful exciting cause of variability. When we see the symmetrical and
complex outgrowths, caused by a minute drop of the poison of a gall-insect, we
may believe that slight changes in the chemical nature of the sap or blood
would lead to extraordinary modifications of structure.

The increased use of a muscle with its various attached parts, and the
increased activity of a gland or other organ, lead to their increased
development. Disuse has a contrary effect. With domesticated productions,
although their organs sometimes become rudimentary through abortion, we have
no reason to suppose that this has ever followed solely from disuse. With
natural species, on the contrary, many organs appear to have been rendered
rudimentary through disuse, aided by the principle of the economy of growth
together with intercrossing. Complete abortion can be accounted for only by
the hypothesis given in the last chapter, namely, the final destruction of the
germs or gemmules of useless parts. This difference between species and
domestic varieties may be partly accounted for by disuse having acted on the
latter for an insufficient length of time, and partly from their exemption
from any severe struggle for existence entailing rigid economy in the
development of each part, to which all species under nature are subjected.
Nevertheless the law of compensation or balancement, which likewise depends on
the economy of growth, apparently has affected to a certain extent our
domesticated productions.

As almost every part of the organisation becomes highly variable under
domestication, and as variations are easily selected both consciously and
unconsciously, it is very difficult to distinguish between the effects of the
selection of indefinite variations and the direct action of the conditions of
life. For instance, it is possible that the feet of our water-dogs and of the
American dogs which have to travel much over the snow, may have become
partially webbed from the stimulus of widely extending their toes; but it is
more probable that the webbing, like the membrane between the toes of certain
pigeons, spontaneously appeared and was afterwards increased by the best
swimmers and the best snow-travellers being preserved during many generations.
A fancier who wished to decrease the size of his bantams or tumbler-pigeons
would never think of starving them, but would select the smallest individuals
which spontaneously appeared. Quadrupeds are sometimes born destitute of hair
and hairless breeds have been formed, but there is no reason to believe that
this is caused by a hot climate. Within the tropics heat often causes sheep to
lose their fleeces; on the other hand, wet and cold act as a direct stimulus
to the growth of hair; but who will pretend to decide how far the thick fur of
arctic animals, or their white colour, is due to the direct action of a severe
climate, and how far to the preservation of the best-protected individuals
during a long succession of generations?

Of all the laws governing variability, that of correlation is one of the most
important. In many cases of slight deviations of structure as well as of grave
monstrosities, we cannot even conjecture what is the nature of the bond of
connexion. But between homologous parts--between the fore and hind limbs--
between the hair, hoofs, horns, and teeth--which are closely similar during
their early development and which are exposed to similar conditions, we can
see that they would be eminently liable to be modified in the same manner.
Homologous parts, from having the same nature, are apt to blend together, and,
when many exist, to vary in number.

Although every variation is either directly or indirectly caused by some
change in the surrounding conditions, we must never forget that the nature of
the organisation which is acted on, is by far the more important factor in the
result. We see this in different organisms, which when placed under similar
conditions vary in a different manner, whilst closely-allied organisms under
dissimilar conditions often vary in nearly the same manner. We see this, in
the same modification frequently reappearing in the same variety at long
intervals of time, and likewise in the several striking cases given of
analogous or parallel variations. Although some of these latter cases are due
to reversion, others cannot thus be accounted for.

From the indirect action of changed conditions on the organisation, owing to
the reproductive organs being thus affected--from the direct action of such
conditions, and these will cause the individuals of the same species either to
vary in the same manner, or differently in accordance with slight differences
in their constitution--from the effects of the increased or decreased use of
parts--and from correlation,--the variability of our domesticated productions
is complicated to an extreme degree. The whole organisation becomes slightly
plastic. Although each modification must have its own exciting cause, and
though each is subjected to law, yet we can so rarely trace the precise
relation between cause and effect, that we are tempted to speak of variations
as if they arose spontaneously. We may even call them accidental, but this
must be only in the sense in which we say that a fragment of rock dropped from
a height owes its shape to accident.

It may be worth while briefly to consider the result of the exposure to
unnatural conditions of a large number of animals of the same species and
allowed to cross freely with no selection of any kind, and afterwards to
consider the result when selection is brought into play. Let us suppose that
500 wild rock-pigeons were confined in their native land in an aviary and fed
in the same manner as pigeons usually are; and that they were not allowed to
increase in number. As pigeons propagate so rapidly, I suppose that a thousand
or fifteen hundred birds would have to be annually killed. After several
generations had been thus reared, we may feel sure that some of the young
birds would vary, and the variations would tend to be inherited; for at the
present day slight deviations of structure often occur and are inherited. It
would be tedious even to enumerate the multitude of points which still go on
varying or have recently varied. Many variations would occur in correlation
with one another, as the length of the wing and tail feathers--the number of
the primary wing-feathers, as well as the number and breadth of the ribs, in
correlation with the size and form of the body--the number of the scutellae
with the size of the feet--the length of the tongue with the length of the
beak--the size of the nostrils and eyelids and the form of lower jaw in
correlation with the development of wattle--the nakedness of the young with
the future colour of the plumage--the size of the feet with that of the beak,
and other such points. Lastly, as our birds are supposed to be confined in an
aviary, they would use their wings and legs but little, and certain parts of
the skeleton, such as the sternum, scapulae and feet, would in consequence
become slightly reduced in size.

As in our assumed case many birds have to be indiscriminately killed every
year, the chances are against any new variety surviving long enough to breed.
And as the variations which arise are of an extremely diversified nature, the
chances are very great against two birds pairing which have varied in the same
manner; nevertheless, a varying bird even when not thus paired would
occasionally transmit its character to its young; and these would not only be
exposed to the same conditions which first caused the variation in question to
appear, but would in addition inherit from their modified parent a tendency
again to vary in the same manner. So that, if the conditions decidedly tended
to induce some particular variation, all the birds might in the course of time
become similarly modified. But a far commoner result would be, that one bird
would vary in one way and another bird in another way; one would be born with
a beak a little longer, and another with a shorter beak; one would gain some
black feathers, another some white or red feathers. And as these birds would
be continually intercrossing, the final result would be a body of individuals
differing from each other in many ways, but only slightly; yet more than did
the original rock-pigeons. But there would not be the least tendency towards
the formation of several distinct breeds.

If two separate lots of pigeons were treated in the manner just described, one
in England and the other in a tropical country, the two lots being supplied
with different kinds of food, would they after many generations differ? When
we reflect on the cases given in the twenty-third chapter, and on such facts
as the difference in former times between the breeds of cattle, sheep, etc.,
in almost every district of Europe, we are strongly inclined to admit that the
two lots would be differently modified through the influence of climate and
food. But the evidence on the definite action of changed conditions is in most
cases insufficient; and, with respect to pigeons, I have had the opportunity
of examining a large collection of domesticated kinds, sent to me by Sir W.
Elliot from India, and they varied in a remarkably similar manner with our
European birds.

If two distinct breeds were mingled together in equal numbers, there is reason
to suspect that they would to a certain extent prefer pairing with their own
kind; but they would often intercross. From the greater vigour and fertility
of the crossed offspring, the whole body would by this means become
interblended sooner than would otherwise have occurred. From certain breeds
being prepotent over others, it does not follow that the interblended progeny
would be strictly intermediate in character. I have, also, proved that the act
of crossing in itself gives a strong tendency to reversion, so that the
crossed offspring would tend to revert to the state of the aboriginal rock-
pigeon; and in the course of time they would probably be not much more
heterogeneous in character than in our first case, when birds of the same
breed were confined together.

I have just said that the crossed offspring would gain in vigour and
fertility. From the facts given in the seventeenth chapter there can be no
doubt of this fact; and there can be little doubt, though the evidence on this
head is not so easily acquired, that long-continued close interbreeding leads
to evil results. With hermaphrodites of all kinds, if the sexual elements of
the same individual habitually acted on each other, the closest possible
interbreeding would be perpetual. But we should bear in mind that the
structure of all hermaphrodite animals, as far as I can learn, permits and
frequently necessitates a cross with a distinct individual. With hermaphrodite
plants we incessantly meet with elaborate and perfect contrivances for this
same end. It is no exaggeration to assert that, if the use of the talons and
tusks of a carnivorous animal, or of the plumes and hooks on a seed, may be
safely inferred from their structure, we may with equal safety infer that many
flowers are constructed for the express purpose of ensuring a cross with a
distinct plant. From these various considerations, not to mention the result
of a long series of experiments which I have tried, the conclusion arrived at
in the chapter just referred to--namely, that great good of some kind is
derived from the sexual concourse of distinct individuals--must be admitted.

To return to our illustration: we have hitherto assumed that the birds were
kept down to the same number by indiscriminate slaughter; but if the least
choice be permitted in their preservation, the whole result will be changed.
Should the owner observe any slight variation in one of his birds, and wish to
obtain a breed thus characterised, he would succeed in a surprisingly short
time by careful selection. As any part which has once varied generally goes on
varying in the same direction, it is easy, by continually preserving the most
strongly marked individuals, to increase the amount of difference up to a
high, predetermined standard of excellence. This is methodical selection.

If the owner of the aviary, without any thought of making a new breed, simply
admired, for instance, short-beaked more than long-beaked birds, he would,
when he had to reduce the number, generally kill the latter; and there can be
no doubt that he would thus in the course of time sensibly modify his stock.
It is improbable, if two men were to keep pigeons and act in this manner, that
they would prefer exactly the same characters; they would, as we know, often
prefer directly opposite characters, and the two lots would ultimately come to
differ. This has actually occurred with strains or families of cattle, sheep,
and pigeons, which have been long kept and carefully attended to by different
breeders, without any wish on their part to form new and distinct sub-breeds.
This unconscious kind of selection will more especially come into action with
animals which are highly serviceable to man; for every one tries to get the
best dogs, horses, cows, or sheep, without thinking about their future
progeny, yet these animals would transmit more or less surely their good
qualities to their offspring. Nor is any one so careless as to breed from his
worst animals. Even savages, when compelled from extreme want to kill some of
their animals, would destroy the worst and preserve the best. With animals
kept for use and not for mere amusement, different fashions prevail in
different districts, leading to the preservation, and consequently to the
transmission, of all sorts of trifling peculiarities of character. The same
process will have been pursued with our fruit-trees and vegetables, for the
best will always have been the most largely cultivated, and will occasionally
have yielded seedlings better than their parents.

The different strains, just alluded to, which have been actually produced by
breeders without any wish on their part to obtain such a result, afford
excellent evidence of the power of unconscious selection. This form of
selection has probably led to far more important results than methodical
selection, and is likewise more important under a theoretical point of view
from closely resembling natural selection. For during this process the best or
most valued individuals are not separated and prevented from crossing with
others of the same breed, but are simply preferred and preserved; yet this
inevitably leads to their gradual modification and improvement; so that
finally they prevail, to the exclusion of the old parent-form.

With our domesticated animals natural selection checks the production of races
with any injurious deviation of structure. In the case of animals which, from
being kept by savages or semi-civilised people, have to provide largely for
their own wants under different circumstances, natural selection will have
played a more important part. Hence it probably is that they often closely
resemble natural species.

As there is no limit to man's desire to possess animals and plants more and
more useful in any respect, and as the fancier always wishes, owing to
fashions running into extremes, to produce each character more and more
strongly pronounced, there is, through the prolonged action of methodical and
unconscious selection, a constant tendency in every breed to become more and
more different from its parent-stock; and when several breeds have been
produced and are valued for different qualities, to differ more and more from
each other. This leads to Divergence of Character. As improved sub-varieties
and races are slowly formed, the older and less improved breeds are neglected
and decrease in number. When few individuals of any breed exist within the
same locality, close interbreeding, by lessening their vigour and fertility,
aids in their final extinction. Thus the intermediate links are lost, and the
remaining breeds gain in Distinctness of Character.

In the chapters on the Pigeon, it was proved by historical evidence and by the
existence of connecting sub-varieties in distant lands that several breeds
have steadily diverged in character, and that many old and intermediate sub-
breeds have been lost. Other cases could be adduced of the extinction of
domestic breeds, as of the Irish wolf-dog, the old English hound, and of two
breeds in France, one of which was formerly highly valued. (28/4. M. Rufz de
Lavison in 'Bull. Soc. Imp. d'Acclimat.' December 1862 page 1009.) Mr.
Pickering remarks (28/5. 'Races of Man' 1850 page 315.) that "the sheep
figured on the most ancient Egyptian monuments is unknown at the present day;
and at least one variety of the bullock, formerly known in Egypt, has in like
manner become extinct." So it has been with some animals and with several
plants cultivated by the ancient inhabitants of Europe during the neolithic
period. In Peru, Von Tschudi (28/6. 'Travels in Peru' English translation page
177.) found in certain tombs, apparently prior to the dynasty of the Incas,
two kinds of maize not now known in the country. With our flowers and culinary
vegetables, the production of new varieties and their extinction has
incessantly recurred. At the present time improved breeds sometimes displace
older breeds at an extraordinarily rapid rate; as has recently occurred
throughout England with pigs. The Longhorn cattle in their native home were
"suddenly swept away as if by some murderous pestilence," by the introduction
of Shorthorns. (28/7. Youatt on 'Cattle' 1834 page 200. On Pigs see
'Gardener's Chronicle' 1854 page 410.)

What grand results have followed from the long-continued action of methodical
and unconscious selection, regulated to a certain extent by natural selection,
we see on every side of us. Compare the many animals and plants which are
displayed at our exhibitions with their parent-forms when these are known, or
consult old historical records with respect to their former state. Most of our
domesticated animals have given rise to numerous and distinct races, but those
which cannot be easily subjected to selection must be excepted--such as cats,
the cochineal insect, and the hive-bee. In accordance with what we know of the
process of selection, the formation of our many races has been slow and
gradual. The man who first observed and preserved a pigeon with its oesophagus
a little enlarged, its beak a little longer, or its tail a little more
expanded than usual, never dreamed that he had made the first step in the
creation of a pouter, carrier, and fantail-pigeon. Man can create not only
anomalous breeds, but others having their whole structure admirably co-
ordinated for certain purposes, such as the racehorse and dray-horse, or the
greyhound and bulldog. It is by no means necessary that each small change of
structure throughout the body, leading towards excellence, should
simultaneously arise and be selected. Although man seldom attends to
differences in organs which are important under a physiological point of view,
yet he has so profoundly modified some breeds, that assuredly, if found wild,
they would be ranked as distinct genera.

The best proof of what selection has effected is perhaps afforded by the fact
that whatever part or quality in any animal, and more especially in any plant,
is most valued by man, that part or quality differs most in the several races.
This result is well seen by comparing the amount of difference between the
fruits produced by the several varieties of fruit-trees, between the flowers
of our flower-garden plants, between the seeds, roots, or leaves of our
culinary and agricultural plants, in comparison with the other and not valued
parts of the same varieties. Striking evidence of a different kind is afforded
by the fact ascertained by Oswald Heer (28/8. 'Die Pflanzen der Pfahlbauten'
1865.) namely, that the seeds of a large number of plants,--wheat, barley,
oats, peas, beans, lentils, poppies,--cultivated for their seed by the ancient
Lake-inhabitants of Switzerland, were all smaller than the seeds of our
existing varieties. Rutimeyer has shown that the sheep and cattle which were
kept by the earlier Lake-inhabitants were likewise smaller than our present
breeds. In the middens of Denmark, the earliest dog of which the remains have
been found was the weakest; this was succeeded during the Bronze age by a
stronger kind, and this again during the Iron age by one still stronger. The
sheep of Denmark during the Bronze period had extraordinarily slender limbs,
and the horse was smaller than our present animal. (28/9. Morlot 'Soc. Vaud.
des Scien. Nat.' Mars 1860 page 298.) No doubt in most of these cases the new
and larger breeds were introduced from foreign lands by the immigration of new
hordes of men. But it is not probable that each larger breed, which in the
course of time has supplanted a previous and smaller breed, was the descendant
of a distinct and larger species; it is far more probable that the domestic
races of our various animals were gradually improved in different parts of the
great Europaeo-Asiatic continent, and thence spread to other countries. This
fact of the gradual increase in size of our domestic animals is all the more
striking as certain wild or half-wild animals, such as red-deer, aurochs,
park-cattle, and boars (28/10. Rutimeyer 'Die Fauna der Pfahlbauten' 1861 s.
30.) have within nearly the same period decreased in size.

The conditions favourable to selection by man are,--the closest attention to
every character,--long-continued perseverance,--facility in matching or
separating animals,--and especially a large number being kept, so that the
inferior individuals may be freely rejected or destroyed, and the better ones
preserved. When many are kept there will also be a greater chance of the
occurrence of well-marked deviations of structure. Length of time is all-
important; for as each character, in order to become strongly pronounced, has
to be augmented by the selection of successive variations of the same kind,
this can be effected only during a long series of generations. Length of time
will, also, allow any new feature to become fixed by the continued rejection
of those individuals which revert or vary, and by the preservation of those
which still inherit the new character. Hence, although some few animals have
varied rapidly in certain respects under new conditions of life, as dogs in
India and sheep in the West Indies, yet all the animals and plants which have
produced strongly marked races were domesticated at an extremely remote epoch,
often before the dawn of history. As a consequence of this, no record has been
preserved of the origin of our chief domestic breeds. Even at the present day
new strains or sub-breeds are formed so slowly that their first appearance
passes unnoticed. A man attends to some particular character, or merely
matches his animals with unusual care, and after a time a slight difference is
perceived by his neighbours;--the difference goes on being augmented by
unconscious and methodical selection, until at last a new sub-breed is formed,
receives a local name, and spreads; but by this time its history is almost
forgotten. When the new breed has spread widely, it gives rise to new strains
and sub-breeds, and the best of these succeed and spread, supplanting other
and older breeds; and so always onwards in the march of improvement.

When a well-marked breed has once been established, if not supplanted by still
further improved sub-breeds, and if not exposed to greatly changed conditions
of life inducing further variability or reversion to long-lost characters, it
may apparently last for an enormous period. We may infer that this is the case
from the high antiquity of certain races; but some caution is necessary on
this head, for the same variation may appear independently after long
intervals of time, or in distant places. We may safely assume that this has
occurred with the turnspit-dog, of which one is figured on the ancient
Egyptian monuments--with the solid-hoofed swine (28/11. Godron 'De l'Espece'
tome 1 1859 page 368.) mentioned by Aristotle--with five-toed fowls described
by Columella--and certainly with the nectarine. The dogs represented on the
Egyptian monuments, about 2000 B.C., show us that some of the chief breeds
then existed, but it is extremely doubtful whether any are identically the
same with our present breeds. A great mastiff sculptured on an Assyrian tomb,
640 B.C., is said to be the same with the dog still imported from Thibet into
the same region. The true greyhound existed during the Roman classical period.
Coming down to a later period, we have seen that, though most of the chief
breeds of the pigeon existed between two and three centuries ago, they have
not all retained exactly the same character to the present day; but this has
occurred in certain cases in which no improvement was desired, for instance,
in the case of the Spot and Indian ground-tumbler.

De Candolle (28/12. 'Geographie Botan.' 1855 page 989.) has fully discussed
the antiquity of various races of plants; he states that the black seeded
poppy was known in the time of Homer, the white-seeded sesamum by the ancient
Egyptians, and almonds with sweet and bitter kernels by the Hebrews; but it
does not seem improbable that some of these varieties may have been lost and
reappeared. One variety of barley and apparently one of wheat, both of which
were cultivated at an immensely remote period by the Lake-inhabitants of
Switzerland, still exist. It is said (28/13. Pickering 'Races of Man' 1850
page 318.) that "specimens of a small variety of gourd which is still common
in the market of Lima were exhumed from an ancient cemetery in Peru." De
Candolle remarks that, in the books and drawings of the sixteenth century, the
principal races of the cabbage, turnip, and gourd can be recognised: this
might have been expected at so late a period, but whether any of these plants
are absolutely identical with our present sub-varieties is not certain. It is,
however, said that the Brussels sprout, a variety which in some places is
liable to degeneration, has remained genuine for more than four centuries in
the district where it is believed to have originated. (28/14. 'Journal of a
Horticultural Tour' by a Deputation of the Caledonian Hist. Soc. 1823 page

In accordance with the views maintained by me in this work and elsewhere, not
only the various domestic races, but the most distinct genera and orders
within the same great class--for instance, mammals, birds, reptiles, and
fishes--are all the descendants of one common progenitor, and we must admit
that the whole vast amount of difference between these forms has primarily
arisen from simple variability. To consider the subject under this point of
view is enough to strike one dumb with amazement. But our amazement ought to
be lessened when we reflect that beings almost infinite in number, during an
almost infinite lapse of time, have often had their whole organisation
rendered in some degree plastic, and that each slight modification of
structure which was in any way beneficial under excessively complex conditions
of life has been preserved, whilst each which was in any way injurious has
been rigorously destroyed. And the long-continued accumulation of beneficial
variations will infallibly have led to structures as diversified, as
beautifully adapted for various purposes and as excellently co-ordinated, as
we see in the animals and plants around us. Hence I have spoken of selection
as the paramount power, whether applied by man to the formation of domestic
breeds, or by nature to the production of species. I may recur to the metaphor
given in a former chapter: if an architect were to rear a noble and commodious
edifice, without the use of cut stone, by selecting from the fragments at the
base of a precipice wedge-formed stones for his arches, elongated stones for
his lintels, and flat stones for his roof, we should admire his skill and
regard him as the paramount power. Now, the fragments of stone, though
indispensable to the architect, bear to the edifice built by him the same
relation which the fluctuating variations of organic beings bear to the varied
and admirable structures ultimately acquired by their modified descendants.

Some authors have declared that natural selection explains nothing, unless the
precise cause of each slight individual difference be made clear. If it were
explained to a savage utterly ignorant of the art of building, how the edifice
had been raised stone upon stone, and why wedge-formed fragments were used for
the arches, flat stones for the roof, etc.; and if the use of each part and of
the whole building were pointed out, it would be unreasonable if he declared
that nothing had been made clear to him, because the precise cause of the
shape of each fragment could not be told. But this is a nearly parallel case
with the objection that selection explains nothing, because we know not the
cause of each individual difference in the structure of each being.

The shape of the fragments of stone at the base of our precipice may be called
accidental, but this is not strictly correct; for the shape of each depends on
a long sequence of events, all obeying natural laws; on the nature of the
rock, on the lines of deposition or cleavage, on the form of the mountain,
which depends on its upheaval and subsequent denudation, and lastly on the
storm or earthquake which throws down the fragments. But in regard to the use
to which the fragments may be put, their shape may be strictly said to be
accidental. And here we are led to face a great difficulty, in alluding to
which I am aware that I am travelling beyond my proper province. An omniscient
Creator must have foreseen every consequence which results from the laws
imposed by Him. But can it be reasonably maintained that the Creator
intentionally ordered, if we use the words in any ordinary sense, that certain
fragments of rock should assume certain shapes so that the builder might erect
his edifice? If the various laws which have determined the shape of each
fragment were not predetermined for the builder's sake, can it be maintained
with any greater probability that He specially ordained for the sake of the
breeder each of the innumerable variations in our domestic animals and
plants;--many of these variations being of no service to man, and not
beneficial, far more often injurious, to the creatures themselves? Did He
ordain that the crop and tail-feathers of the pigeon should vary in order that
the fancier might make his grotesque pouter and fantail breeds? Did He cause
the frame and mental qualities of the dog to vary in order that a breed might
be formed of indomitable ferocity, with jaws fitted to pin down the bull for
man's brutal sport? But if we give up the principle in one case,--if we do not
admit that the variations of the primeval dog were intentionally guided in
order that the greyhound, for instance, that perfect image of symmetry and
vigour, might be formed,--no shadow of reason can be assigned for the belief
that variations, alike in nature and the result of the same general laws,
which have been the groundwork through natural selection of the formation of
the most perfectly adapted animals in the world, man included, were
intentionally and specially guided. However much we may wish it, we can hardly
follow Professor Asa Gray in his belief "that variation has been led along
certain beneficial lines," like a stream "along definite and useful lines of
irrigation." If we assume that each particular variation was from the
beginning of all time preordained, then that plasticity of organisation, which
leads to many injurious deviations of structure, as well as the redundant
power of reproduction which inevitably leads to a struggle for existence, and,
as a consequence, to the natural selection or survival of the fittest, must
appear to us superfluous laws of nature. On the other hand, an omnipotent and
omniscient Creator ordains everything and foresees everything. Thus we are
brought face to face with a difficulty as insoluble as is that of free will
and predestination.


ABBAS PACHA, a fancier of fantailed pigeons.

ABBEY, Mr., on grafting.
-on mignonette.

ABBOTT, Mr. Keith, on the Persian tumbler pigeon.

ABBREVIATION of the facial bones.

ABORTION of organs.

ABSORPTION of minority in crossed races.

ABUTILON, graft hybridisation of.


ACERBI, on the fertility of domestic animals in Lapland.


Achillea millefolium, bud variation in.

Aconitum napellus, roots of, innocuous in cold climates.

Acorus calamus, sterility of.

ACOSTA, on fowls in South America at its discovery.

Acropera, number of seeds in.

ADAM, M., origin of Cytisus adami.

ADAM, W., on consanguineous marriages.

ADAMS, on hereditary diseases.

ADVANCEMENT in scale of organisation.

Aegilops triticoides, observations of Fabre and Godron on.
-increasing fertility of hybrids of, with wheat.

Aesculus pavia, tendency of, to become double.

Aethusa cynapium.

AFFINITY, sexual elective.

AFRICA, white bull from.
-feral cattle in.
-food-plants of savages of.
-South, diversity of breeds of cattle in.
-West, change in fleece of sheep in.

Agave vivipara, seeding of, in poor soil.

AGE, changes in trees, dependent on.
-as bearing on pangenesis.

AGOUTI, fertility of, in captivity.

AGRICULTURE, antiquity of.

Agrostis, seeds of, used as food.


AINSWORTH, Mr., on the change in the hair of animals at Angora.

AKBAR KHAN, his fondness for pigeons,

Alauda arvensis.

ALBIN, on "Golden Hamburgh" fowls.
-figure of the hook-billed duck.


ALBINO, negro, attacked by insects.

ALBINOES, heredity of.

ALBINUS, thickness of the epidermis on the palms of the hands in man.


ALDROVANDI, on rabbits.
-description of the nun pigeon.
-on the fondness of the Dutch for pigeons in the seventeenth century.
-notice of several varieties of pigeons.
-on the breeds of fowls.
-on the origin of the domestic duck.

ALEFIELD, Dr., on the varieties of peas and their specific unity.
-on the varieties of beans.

ALEXANDER the Great, his selection of Indian cattle.

ALGAE, retrogressive metamorphosis in.
-division of zoospores of,

ALLEN, J., birds in United States.

ALLEN, W., on feral fowls.

ALLMAN, Professor, on a monstrous Saxifraga geum.
-on the Hydroida.

ALMOND, antiquity of.
-bitter, not eaten by mice.

Alnus glutinosa, and incana, hybrids of.

ALPACA, selection of.

Althaea rosea.


Amaryllis vittata, effect of foreign pollen on.

AMAUROSIS, hereditary.

Amblystoma lurida.

AMERICA, limits within which no useful plants have been furnished by.
-colours of feral horses in.
-North, native cultivated plants of.
-skin of feral pig from.
-South, variations in cattle of.

AMMON, on the persistency of colour in horses.

Amygdalus persica.

Anagallis arvensis.

ANALOGOUS variation.
-in horses,
-in the horse and ass.
-in fowls.

Anas boschas.
-skull of, figured.

"ANCON" sheep of Massachusetts.



ANDERSON, J., on the origin of British sheep.
-on the selection of qualities in cattle.
-on a one-eared breed of rabbits.
-on the inheritance of characters from a one-eared rabbit, and three-legged
-on the persistency of varieties of peas.
-on the production of early peas by selection.
-on the varieties of the potato.
-on crossing varieties of the melon.
-on reversion in the barberry.

ANDERSON, Mr., on the reproduction of the weeping ash by seed.
-on the cultivation of the tree paeony in China.

ANDERSSON, Mr., on the Damara, Bechuana, and Namaqua cattle.
-on the cows of the Damaras.
-selection practised by the Damaras and Namaquas.
-on the use of grass-seeds and the roots of reeds as food in South Africa.

Anemone coronaria, doubled by selection.

ANGINA pectoris, hereditary, occurring at a certain age.

ANGLESEA, cattle of.

ANGOLA sheep.

ANGORA, change in hair of animals at.
-cats of.
-rabbits of,

ANIMALS, domestication of, facilitated by fearlessness of man.
-refusal of wild, to breed in captivity.
-compound, individual peculiarities of, reproduced by budding.
-variation by selection in useful qualities of.

ANNUAL plants, rarity of bud-variation in.

ANOMALIES in the osteology of the horse.

ANOMALOUS breeds of pigs.
-of cattle.

Anser albifrons, characters of, reproduced in domestic geese.

Anser aegyptiacus.

Anser canadensis.

Anser ferus, the original of the domestic goose.
-fertility of cross of, with domestic goose.

ANSON, on feral fowls in the Ladrones.

ANTAGONISM between growth and reproduction.

Anthemis nobilis, bud-variation in flowers of.
-becomes single in poor soil.

ANTHERS, contabescence of.

ANTIGUA, cats of.
-changed fleece of sheep in.

Antirrhinum majus, peloric.
-bud-variation in.

ANTS, individual recognition of.

APHIDES, attacking pear-trees.
-development of.

APOPLEXY, hereditary, occurring at a certain age.

-fruit of, in Swiss lake-dwellings.
-rendered fastigiate by heat in India.
-bud-variation in the.
-with dimidiate fruit.
-with two kinds of fruit on the same branch.
-artificial fecundation of.
-St. Valery.
-reversion in seedlings of.
-crossing of varieties of.
-growth of the, in Ceylon.
-winter majetin, not attacked by coccus.
-flower-buds of, attacked by bullfinches.
-American, change of, when grown in England.

-glands on the leaves of.
-analogous variation in the.

Aquila fusca, copulating in captivity.

Aquilegia vulgaris.

ARAB boarhound, described by Harcourt.

Arabis blepharophylla and A. soyeri, effects of crossing.

Aralia trifoliata, bud-variation in leaves of.

ARAUCARIAS, young, variable resistance of, to frost.


ARCTIC regions, variability of plants and shells of.

Aria vestita, grafted on thorns.

ARISTOPHANES, fowls mentioned by.

ARISTOTLE, on solid-hoofed pigs.
-domestic duck unknown to.
-on the assumption of male characters by old hens.

ARNI, domestication of the.

ARNOLD, Mr., experiments of pollen on the maize.

ARRESTS of development.

ARTERIES, increase of anastomosing branches of, when tied.

ARU Islands, wild pig of.

ARUM, Polynesian varieties of.

Ascaris, number of eggs of.

ASH, varieties of the.
-bud-variation in.
-effects of graft upon the stock in the.
-production of the blotched Breadalbane.
-weeping, capricious reproduction of, by seed.

Asinus burchellii.

Asinus hemionus.

Asinus indicus.

Asinus quagga.

Asinus taeniopus, the original of the domestic ass.

ASPARAGUS, increased fertility of cultivated.

ASS, early domestication of the.
-breeds of.
-small size of, in India.
-stripes of.
-dislike of, to cross water.
-reversion in.
-hybrid of the, with mare and zebra.
-prepotency of the, over the horse.
-crossed with wild ass.
-variation and selection of the.

ASSYRIAN sculpture of a mastiff.


ASTHMA, hereditary.

ATAVISM. See Reversion.

ATHELSTAN, his care of horses.

ATKINSON, Mr., on the sterility of the Tarroo silk-moth in confinement.


AUDUBON, on feral hybrid ducks.
-on the domestication of wild ducks on the Mississippi.
-on the wild cock turkey visiting domestic hens.
-fertility of Fringilla ciris in captivity.
-fertility of Columba migratoria and leucocephala in captivity.
-breeding of Anser canadensis in captivity.

AUDUBON and Bachman, on the change of coat in Ovis montana.
-sterility of Sciurus cinerea in confinement.

AURICULA, effect of seasonal conditions on the.
-blooming of.

AUSTRALIA, no generally useful plants derived from.
-useful plants of, enumerated by Hooker.

AUSTRIA, heredity of character in emperors of.

AUTENRIETH, on persistency of colour in horses.

AVA, horses of.

Avena fatua, cultivability of.

'AYEEN Akbery' pigeons mentioned in the.

AYRES, W.P., on bud-variation in pelargoniums.

Azalea indica, bud-variation in.

AZARA, on the feral dogs of La Plata.
-on the crossing of domestic with wild cats in Paraguay.
-on hornlike processes in horses.
-on curled hair in horses.
-on the colours of feral horses.
-on the cattle of Paraguay and La Plata.
-on a hornless bull.
-on the increase of cattle in South America.
-on the growth of horns in the hornless cattle of Corrientes.
-on the "Niata" cattle.
-on naked quadrupeds.
-on a race of black-skinned fowls in South America.
-on a variety of maize.

BABINGTON, C.C., on the origin of the plum.
-British species of the genus Rosa.
-distinctness of Viola lutea and tricolor.

BACHMANN, Mr., on the turkey.
See also Audubon.

BADGER, breeding in confinement.


BAILY, Mr., on the effect of selection on fowls.
-on Dorking fowls.

BAIRD, S., on the origin of the turkey.

BAKER, Mr., on heredity in the horse.
-on the degeneration of the horse by neglect.
-orders of Henrys VII. and VIII. for the destruction of undersized mares.

BAKEWELL, change in the sheep effected by.

-of growth,
-law of.

BALDHEAD (pigeon).

BALDNESS, in man, inherited.
-with deficiency in teeth.

BALLANCE, Mr., on the effects of interbreeding on fowls.
-on variation in the eggs of fowls.

Ballota nigra, transmission of variegated leaves in.

BAMBOO, varieties of the.

BANANA, variation of the.
-bud-variation in the.
-sterility of the.

BANTAM fowls, Sebright, origin of.
-sterility of.

BARB (pigeon).
-figure of.
-figure of lower jaw of.

BARBS, of wheat.

BARBERRY, dark or red-leaved variety.
-reversion in suckers of seedless variety.

BARBUT, J., on the dogs of Guinea.
-on the domestic pigeons in Guinea.
-fowls not native in Guinea.

BARKING, acquisition of the habit of, by various dogs.

BARLEY, wild.
-of the lake-dwellings.
-ancient variety of.

BARNES, Mr., production of early peas by selection.

BARNET, Mr., on the intercrossing of strawberries.
-dioeciousness of the hautbois strawberry.
-on the Scarlet American strawberry.

BARTH, Dr., use of grass-seeds as food in Central Africa.

BARTLETT, A.D., on the origin of "Himalayan" rabbits by intercrossing.
-on the feral rabbits of Porto Santo.
-on geese with reversed feathers on the head and neck.
-on the young of the black-shouldered peacock.
-on a variety of the turkey.
-size of hybrids.
-on the breeding of the Felidae in captivity.
-so-called hybrids.

BARTRAM, on the black wolf-dog of Florida.

BATES, H.W., refusal of wild animals to breed in captivity.
-sterility of American monkeys in captivity.
-sterility of tamed guans.

BATRACHIA, regeneration of lost parts in.

BEACH, raised, in Peru, containing heads of maize.

BEAK, variability of, in fowls.
-individual differences of, in pigeons,
-correlation of, with the feet in pigeons.

BEALE, Lionel, on the contents of cells,
-on the multiplication of infectious atoms.

BEANS, of Swiss lake-dwellings.
-varieties of, produced by selection.
-French and scarlet, variable resistance of, to frost.
-superiority of native seed of.
-a symmetrical variation of scarlet.
-experiments on kidney.
-with monstrous stipules and abortive leaflets.

BEARD pigeon.

BEARS, breeding in captivity.

BEASLEY, J., reversion in crossed cattle.

BEATON, D., effect of soil upon strawberries.
-on varieties of pelargonium.
-bud-variation in Gladiolus colvilii.
-cross between Scotch kail and cabbage.
-hybrid gladiolus.
-constant occurrence of new forms among seedlings.
-on the doubling of the Compositae.

BECHUANA cattle.

BECHSTEIN, on the burrowing of wolves.
-Spitz Dog.
-origin of the Newfoundland dog.
-crossing of domestic and wild swine.
-on the Jacobin pigeon.
-notice of swallow-pigeons.
-on a fork-tailed pigeon.
-variations in the colour of the croup in pigeons.
-on the German dovecote pigeon.
-fertility of mongrel-pigeons.
-on hybrid turtle-doves.
-on crossing the pigeon with Columba oenas, C. palumbus, Turtur risoria, and
T. vulgaris.
-development of spurs in the silk hen.
-on Polish fowls.
-on crested birds.
-on the canary-bird.
-German superstition about the turkey.
-occurrence of horns in hornless breeds of sheep.
-hybrids of the horse and ass.
-crosses of tailless fowls.
-difficulty of pairing dovecote and fancy pigeons.
-fertility of tame ferrets and rabbits.
-fertility of wild sow.
-difficulty of breeding caged birds.
-comparative fertility of Psittacus erithacus in captivity.
-on changes of plumage in captivity,
-liability of light-coloured cattle to the attacks of flies.
-want of exercise a cause of variability.
-effect of privation of light upon the plumage of birds.
-on a sub-variety of the monk-pigeon.

BECK, Mr., constitutional differences in pelargoniums.

BECKMANN, on changes in the odours of plants.

BEDDOE, Dr., correlation of complexion with consumption.

BEE, persistency of character of.
-conveyance of pollen of peas by.

BEE OPHRYS, self-fertilisation of.

BEECH, dark-leaved.
-fern-leaved, reversion of.
-weeping, non-production of, by seed.

BEECHEY, horses of Loochoo Islands.

BEET, increase of sugar in, by selection.

Begonia frigida, singular variety of.
-sterility of.

BELGIAN rabbit.

BELL, T., statement that white cattle have coloured ears.

BELL, W., bud-variation in Paritium tricuspis.

BELLINGERI, observations on gestation in the dog.
-on the fertility of dogs and cats.

BELON, on high-flying pigeons in Paphlagonia.
-varieties of the goose.

BENGUELA, cattle of.

BENNETT, Dr. G., pigs of the Pacific Islands.
-dogs of the Pacific Islands.
-varieties of cultivated plants in Tahiti.

BENNETT, Mr., on the fallow deer.

BENTHAM, G., number and origin of cultivated plants.
-on Phaseolus.
-cereals all cultivated varieties.
-species of the orange group.
-distinctions of almond and peach.
-British species of Rosa.
-identity of Viola lutea and tricolor.

Berberis vulgaris.

Berberis wallichii, indifference of, to climate.

BERJEAU, on the history of the dog.

BERKELEY, G.F., production of hen-cocks in a strain of game-fowls.

BERKELEY, M.J., crossing of varieties of the pea.
-effect of foreign pollen on grapes.
-on hybrid plants.
-analogy between pollen of highly-cultivated plants and hybrids.
-on Hungarian kidney-beans.
-failure of Indian wheat in England.

BERNARD, inheritance of disease in the horse.

BERNARD, C., independence of the organs of the body.
-special affinities of the tissues.

BERNHARDI, varieties of plants with laciniated leaves.

Bernicla antarctica.

BERTERO, on feral pigeons in Juan Fernandez.

Betula alba.

BEWICK, on the British wild cattle.

BIANCONI, Prof., on the skulls of dogs.

BIBLE, reference to breeding studs of horses in.
-references to domestic pigeons in the.
-indications of selection of sheep in the.
-notice of mules in the.

BIDWELL, Mr., on self-impotence in Amaryllis.

Bignonia, self-sterility of.

BIRCH, weeping.

BIRCH, Dr. S., on the ancient domestication of the pigeon in Egypt.
-notice of bantam fowls in a Japanese encyclopaedia.

BIRCH, WYRLEY, on silver-grey rabbits.

BIRDS, sterility caused in, by change of conditions.

BLADDER-NUT, tendency of the, to become double.

BLAINE, Mr., on wry-legged terriers.

BLAINVILLE, origin and history of the dog.
-variations in the number of teeth in dogs.
-variations in the number of toes in dogs.
-on mummies of cats.
-on the osteology of solid-hoofed pigs.
-on feral Patagonian and N. American pigs.


BLEEDING, hereditary.
-sexual limitation of excessive.

BLENDING of crossed races, time occupied by the.

BLINDNESS, hereditary.
-at a certain age.
-associated with colour of hair.

BLOODHOUNDS, degeneration of, caused by interbreeding.

BLUMENBACH, on the protuberance of the skull in Polish fowls.
-on the effect of circumcision.
-inheritance of a crooked finger.
-on badger-dogs and other varieties of the dog.
-on Hydra.
-on the "nisus formativus."

BLYTH, E., on the pariah dog.
-hybrids of dog and jackal.
-early domestication of cats in India.
-origin of domestic cat.
-crossing of domestic and wild cats.
-on Indian cats resembling Felis chaus.
-on striped Burmese ponies.
-on the stripes of the ass.
-on Indian wild pigs.
-on humped cattle.
-occurrence of Bos frontosus in Irish crannoges.
-fertile crossing of zebus and common cattle.
-on the species of sheep.
-on the fat-tailed Indian sheep.
-origin of the goat.
-on rabbits breeding in India.
-number of tail-feathers in fantails.
-Lotan tumbler pigeons.

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