The Origin of Species
Chapter 1: Variation Under Domestication
by Charles Darwin
Causes of Variability - Effects of Habit - Correlation of Growth -
Inheritance - Character of Domestic Varieties - Difficulty of distinguishing between
Varieties and Species - Origin of Domestic Varieties from one or more Species - Domestic
pigeons, their Differences and Origin - Principle of Selection anciently followed, its
Effects - Methodical and Unconscious Selection - Unknown Origin of our Domestic
Productions - Circumstances favourable to Man's power of Selection |
When we look to the individuals of the same variety or sub-variety of
our older cultivated plants and animals, one of the first points which strikes us, is,
that they generally differ much more from each other, than do the individuals of any one
species or variety in a state of nature. When we reflect on the vast diversity of the
plants and animals which have been cultivated, and which have varied during all ages under
the most different climates and treatment, I think we are driven to conclude that this
greater variability is simply due to our domestic productions having been raised under
conditions of life not so uniform as, and somewhat different from, those to which the
parent-species have been exposed under nature. There is, also, I think, some probability
in the view propounded by Andrew Knight, that this variability may be partly connected
with excess of food. It seems pretty clear that organic beings must be exposed during
several generations to the new conditions of life to cause any appreciable amount of
variation; and that when the organisation has once begun to vary, it generally continues
to vary for many generations. No case is on record of a variable being ceasing to be
variable under cultivation. Our oldest cultivated plants, such as wheat, still often yield
new varieties: our oldest domesticated animals are still capable of rapid improvement or
modification.
It has been disputed at what period of time the causes of variability, whatever they
may be, generally act; whether during the early or late period of development of the
embryo, or at the instant of conception. Geoffroy St Hilaire's experiments show that
unnatural treatment of the embryo causes monstrosities; and monstrosities cannot be
separated by any clear line of distinction from mere variations. But I am strongly
inclined to suspect that the most frequent cause of variability may be attributed to the
male and female reproductive elements having been affected prior to the act of conception.
Several reasons make me believe in this; but the chief one is the remarkable effect which
confinement or cultivation has on the functions of the reproductive system; this system
appearing to be far more susceptible than any other part of the organization, to the
action of any change in the conditions of life. Nothing is more easy than to tame an
animal, and few things more difficult than to get it to breed freely under confinement,
even in the many cases when the male and female unite. How many animals there are which
will not breed, though living long under not very close confinement in their native
country! This is generally attributed to vitiated instincts; but how many cultivated
plants display the utmost vigour, and yet rarely or never seed! In some few such cases it
has been found out that very trifling changes, such as a little more or less water at some
particular period of growth, will determine whether or not the plant sets a seed. I cannot
here enter on the copious details which I have collected on this curious subject; but to
show how singular the laws are which determine the reproduction of animals under
confinement, I may just mention that carnivorous animals, even from the tropics, breed in
this country pretty freely under confinement, with the exception of the plantigrades or
bear family; whereas, carnivorous birds, with the rarest exceptions, hardly ever lay
fertile eggs. Many exotic plants have pollen utterly worthless, in the same exact
condition as in the most sterile hybrids. When, on the one hand, we see domesticated
animals and plants, though often weak and sickly, yet breeding quite freely under
confinement; and when, on the other hand, we see individuals, though taken young from a
state of nature, perfectly tamed, long-lived, and healthy (of which I could give numerous
instances), yet having their reproductive system so seriously affected by unperceived
causes as to fail in acting, we need not be surprised at this system, when it does act
under confinement, acting not quite regularly, and producing offspring not perfectly like
their parents or variable.
Sterility has been said to be the bane of horticulture; but on this view we owe
variability to the same cause which produces sterility; and variability is the source of
all the choicest productions of the garden. I may add, that as some organisms will breed
most freely under the most unnatural conditions (for instance, the rabbit and ferret kept
in hutches), showing that their reproductive system has not been thus affected; so will
some animals and plants withstand domestication or cultivation, and vary very slightly
perhaps hardly more than in a state of nature.
A long list could easily be given of 'sporting plants;' by this term gardeners mean a
single bud or offset, which suddenly assumes a new and sometimes very different character
from that of the rest of the plant. Such buds can be propagated by grafting, &c., and
sometimes by seed. These 'sports' are extremely rare under nature, but far from rare under
cultivation; and in this case we see that the treatment of the parent has affected a bud
or offset, and not the ovules or pollen. But it is the opinion of most physiologists that
there is no essential difference between a bud and an ovule in their earliest stages of
formation; so that, in fact,'sports' support my view, that variability may be largely
attributed to the ovules or pollen, or to both, having been affected by the treatment of
the parent prior to the act of conception. These cases anyhow show that variation is not
necessarily connected, as some authors have supposed, with the act of generation.
Seedlings from the same fruit, and the young of the same litter, sometimes differ
considerably from each other, though both the young and the parents, as Muller has
remarked, have apparently been exposed to exactly the same conditions of life; and this
shows how unimportant the direct effects of the conditions of life are in comparison with
the laws of reproduction, and of growth, and of inheritance; for had the action of the
conditions been direct, if any of the young had varied, all would probably have varied in
the same manner. To judge how much, in the case of any variation, we should attribute to
the direct action of heat, moisture, light, food, &c., is most difficult: my
impression is, that with animals such agencies have produced very little direct effect,
though apparently more in the case of plants. Under this point of view, Mr Buckman's
recent experiments on plants seem extremely valuable. When all or nearly all the
individuals exposed to certain conditions are affected in the same way, the change at
first appears to be directly due to such conditions; but in some cases it can be shown
that quite opposite conditions produce similar changes of structure. Nevertheless some
slight amount of change may, I think, be attributed to the direct action of the conditions
of life as, in some cases, increased size from amount of food, colour from particular
kinds of food and from light, and perhaps the thickness of fur from climate.
Habit also has a deciding influence, as in the period of flowering with plants when
transported from one climate to another. In animals it has a more marked effect; for
instance, I find in the domestic duck that the bones of the wing weigh less and the bones
of the leg more, in proportion to the whole skeleton, than do the same bones in the
wild-duck; and I presume that this change may be safely attributed to the domestic duck
flying much less, and walking more, than its wild parent. The great and inherited
development of the udders in cows and goats in countries where they are habitually milked,
in comparison with the state of these organs in other countries, is another instance of
the effect of use. Not a single domestic animal can be named which has not in some country
drooping ears; and the view suggested by some authors, that the drooping is due to the
disuse of the muscles of the ear, from the animals not being much alarmed by danger, seems
probable.
There are many laws regulating variation, some few of which can be dimly seen, and will
be hereafter briefly mentioned. I will here only allude to what may be called correlation
of growth. Any change in the embryo or larva will almost certainly entail changes in the
mature animal. In monstrosities, the correlations between quite distinct parts are very
curious; and many instances are given in Isidore Geoffroy St Hilaire's great work on this
subject. Breeders believe that long limbs are almost always accompanied by an elongated
head. Some instances of correlation are quite whimsical; thus cats with blue eyes are
invariably deaf; colour and constitutional peculiarities go together, of which many
remarkable cases could be given amongst animals and plants. From the facts collected by
Heusinger, it appears that white sheep and pigs are differently affected from coloured
individuals by certain vegetable poisons. Hairless dogs have imperfect teeth; long-haired
and coarse-haired animals are apt to have, as is asserted, long or many horns; pigeons
with feathered feet have skin between their outer toes; pigeons with short beaks have
small feet, and those with long beaks large feet. Hence, if man goes on selecting, and
thus augmenting, any peculiarity, he will almost certainly unconsciously modify other
parts of the structure, owing to the mysterious laws of the correlation of growth.
The result of the various, quite unknown, or dimly seen laws of variation is infinitely
complex and diversified. It is well worth while carefully to study the several treatises
published on some of our old cultivated plants, as on the hyacinth, potato, even the
dahlia, &c.; and it is really surprising to note the endless points in structure and
constitution in which the varieties and sub varieties differ slightly from each other. The
whole organization seems to have become plastic, and tends to depart in some small degree
from that of the parental type.
Any variation which is not inherited is unimportant for us. But the number and
diversity of inheritable deviations of structure, both those of slight and those of
considerable physiological importance, is endless. Dr Prosper Lucas's treatise, in two
large volumes, is the fullest and the best on this subject. No breeder doubts how strong
is the tendency to inheritance: like produces like is his fundamental belief: doubts have
been thrown on this principle by theoretical writers alone. When a deviation appears not
unfrequently, and we see it in the father and child, we cannot tell whether it may not be
due to the same original cause acting on both; but when amongst individuals, apparently
exposed to the same conditions, any very rare deviation, due to some extraordinary
combination of circumstances, appears in the parent say, once amongst several million
individuals and it reappears in the child, the mere doctrine of chances almost compels us
to attribute its reappearance to inheritance. Every one must have heard of cases of
albinism, prickly skin, hairy bodies, &c. appearing in several members of the same
family. If strange and rare deviations of structure are truly inherited, less strange and
commoner deviations may be freely admitted to be inheritable. Perhaps the correct way of
viewing the whole subject, would be, to look at the inheritance of every character
whatever as the rule, and non-inheritance as the anomaly.
The laws governing inheritance are quite unknown; no one can say why the same
peculiarity in different individuals of the same species, and in individuals of different
species, is sometimes inherited and sometimes not so; why the child often reverts in
certain characters to its grandfather or grandmother or other much more remote ancestor;
why a peculiarity is often transmitted from one sex to both sexes or to one sex alone,
more commonly but not exclusively to the like sex. It is a fact of some little importance
to us, that peculiarities appearing in the males of our domestic breeds are often
transmitted either exclusively, or in a much greater degree, to males alone. A much more
important rule, which I think may be trusted, is that, at whatever period of life a
peculiarity first appears, it tends to appear in the offspring at a corresponding age,
though sometimes earlier. In many cases this could not be otherwise: thus the inherited
peculiarities in the horns of cattle could appear only in the offspring when nearly
mature; peculiarities in the silkworm are known to appear at the corresponding caterpillar
or cocoon stage. But hereditary diseases and some other facts make me believe that the
rule has a wider extension, and that when there is no apparent reason why a peculiarity
should appear at any particular age, yet that it does tend to appear in the offspring at
the same period at which it first appeared in the parent. I believe this rule to be of the
highest importance in explaining the laws of embryology. These remarks are of course
confined to the first appearance of the peculiarity, and not to its primary cause,
which may have acted on the ovules or male element; in nearly the same manner as in the
crossed offspring from a short-horned cow by a long-horned bull, the greater length of
horn, though appearing late in life, is clearly due to the male element.
Having alluded to the subject of reversion, I may here refer to a statement often made
by naturalists namely, that our domestic varieties, when run wild, gradually but certainly
revert in character to their aboriginal stocks. Hence it has been argued that no
deductions can be drawn from domestic races to species in a state of nature. I have in
vain endeavoured to discover on what decisive facts the above statement has so often and
so boldly been made. There would be great difficulty in proving its truth: we may safely
conclude that very many of the most strongly-marked domestic varieties could not possibly
live in a wild state. In many cases we do not know what the aboriginal stock was, and so
could not tell whether or not nearly perfect reversion had ensued. It would be quite
necessary, in order to prevent the effects of intercrossing, that only a single variety
should be turned loose in its new home. Nevertheless, as our varieties certainly do
occasionally revert in some of their characters to ancestral forms, it seems to me not
improbable, that if we could succeed in naturalising, or were to cultivate, during many
generations, the several races, for instance, of the cabbage, in very poor soil (in which
case, however, some effect would have to be attributed to the direct action of the poor
soil), that they would to a large extent, or even wholly, revert to the wild aboriginal
stock. Whether or not the experiment would succeed, is not of great importance for our
line of argument; for by the experiment itself the conditions of life are changed. If it
could be shown that our domestic varieties manifested a strong tendency to reversion, that
is, to lose their acquired characters, whilst kept under unchanged conditions, and whilst
kept in a considerable body, so that free intercrossing might check, by blending together,
any slight deviations of structure, in such case, I grant that we could deduce nothing
from domestic varieties in regard to species. But there is not a shadow of evidence in
favour of this view: to assert that we could not breed our cart and race-horses, long and
short-horned cattle and poultry of various breeds, and esculent vegetables, for an almost
infinite number of generations, would be opposed to all experience. I may add, that when
under nature the conditions of life do change, variations and reversions of character
probably do occur; but natural selection, as will hereafter be explained, will determine
how far the new characters thus arising shall be preserved.
When we look to the hereditary varieties or races of our domestic animals and plants,
and compare them with species closely allied together, we generally perceive in each
domestic race, as already remarked, less uniformity of character than in true species.
Domestic races of the same species, also, often have a somewhat monstrous character; by
which I mean, that, although differing from each other, and from the other species of the
same genus, in several trifling respects, they often differ in an extreme degree in some
one part, both when compared one with another, and more especially when compared with all
the species in nature to which they are nearest allied. With these exceptions (and with
that of the perfect fertility of varieties when crossed, a subject hereafter to be
discussed), domestic races of the same species differ from each other in the same manner
as, only in most cases in a lesser degree than, do closely-allied species of the same
genus in a state of nature. I think this must be admitted, when we find that there are
hardly any domestic races, either amongst animals or plants, which have not been ranked by
some competent judges as mere varieties, and by other competent judges as the descendants
of aboriginally distinct species. If any marked distinction existed between domestic races
and species, this source of doubt could not so perpetually recur. It has often been stated
that domestic races do not differ from each other in characters of generic value. I think
it could be shown that this statement is hardly correct; but naturalists differ most
widely in determining what characters are of generic value; all such valuations being at
present empirical. Moreover, on the view of the origin of genera which I shall presently
give, we have no right to expect often to meet with generic differences in our
domesticated productions.
When we attempt to estimate the amount of structural difference between the domestic
races of the same species, we are soon involved in doubt, from not knowing whether they
have descended from one or several parent-species. This point, if could be cleared up,
would be interesting; if, for instance, it could be shown that the greyhound, bloodhound,
terrier, spaniel, and bull-dog, which we all know propagate their kind so truly, were the
offspring of any single species, then such facts would have great weight in making us
doubt about the immutability of the many very closely allied and natural species for
instance, of the many foxes inhabiting different quarters of the world. I do not believe,
as we shall presently see, that all our dogs have descended from any one wild species;
but, in the case of some other domestic races, there is presumptive, or even strong,
evidence in favour of this view.
It has often been assumed that man has chosen for domestication animals and plants
having an extraordinary inherent tendency to vary, and likewise to withstand diverse
climates. I do not dispute that these capacities have added largely to the value of most
of our domesticated productions; but how could a savage possibly know, when he first tamed
an animal, whether it would vary in succeeding generations, and whether it would endure
other climates? Has the little variability of the ass or guinea-fowl, or the small power
of endurance of warmth by the reindeer, or of cold by the common camel, prevented their
domestication? I cannot doubt that if other animals and plants, equal in number to our
domesticated productions, and belonging to equally diverse classes and countries, were
taken from a state of nature, and could be made to breed for an equal number of
generations under domestication, they would vary on an average as largely as the parent
species of our existing domesticated productions have varied.
In the case of most of our anciently domesticated animals and plants, I do not think it
is possible to come to any definite conclusion, whether they have descended from one or
several species. The argument mainly relied on by those who believe in the multiple origin
of our domestic animals is, that we find in the most ancient records, more especially on
the monuments of Egypt, much diversity in the breeds; and that some of the breeds closely
resemble, perhaps are identical with, those still existing. Even if this latter fact were
found more strictly and generally true than seems to me to be the case, what does it show,
but that some of our breeds originated there, four or five thousand years ago? But Mr
Horner's researches have rendered it in some degree probable that man sufficiently
civilized to have manufactured pottery existed in the valley of the Nile thirteen or
fourteen thousand years ago; and who will pretend to say how long before these ancient
periods, savages, like those of Tierra del Fuego or Australia, who possess a semi-domestic
dog, may not have existed in Egypt?
The whole subject must, I think, remain vague; nevertheless, I may, without here
entering on any details, state that, from geographical and other considerations, I think
it highly probable that our domestic dogs have descended from several wild species. In
regard to sheep and goats I can form no opinion. I should think, from facts communicated
to me by Mr Blyth, on the habits, voice, and constitution, &c., of the humped Indian
cattle, that these had descended from a different aboriginal stock from our European
cattle; and several competent judges believe that these latter have had more than one wild
parent. With respect to horses, from reasons which I cannot give here, I am doubtfully
inclined to believe, in opposition to several authors, that all the races have descended
from one wild stock. Mr Blyth, whose opinion, from his large and varied stores of
knowledge, I should value more than that of almost any one, thinks that all the breeds of
poultry have proceeded from the common wild Indian fowl (Gallus bankiva). In regard to
ducks and rabbits, the breeds of which differ considerably from each other in structure, I
do not doubt that they all have descended from the common wild duck and rabbit.
The doctrine of the origin of our several domestic races from several aboriginal
stocks, has been carried to an absurd extreme by some authors. They believe that every
race which breeds true, let the distinctive characters be ever so slight, has had its wild
prototype. At this rate there must have existed at least a score of species of wild
cattle, as many sheep, and several goats in Europe alone, and several even within Great
Britain. One author believes that there formerly existed in Great Britain eleven wild
species of sheep peculiar to it! When we bear in mind that Britain has now hardly one
peculiar mammal, and France but few distinct from those of Germany and conversely, and so
with Hungary, Spain, &c., but that each of these kingdoms possesses several peculiar
breeds of cattle, sheep, &c., we must admit that many domestic breeds have originated
in Europe; for whence could they have been derived, as these several countries do not
possess a number of peculiar species as distinct parent-stocks? So it is in India. Even in
the case of the domestic dogs of the whole world, which I fully admit have probably
descended from several wild species, I cannot doubt that there has been an immense amount
of inherited variation. Who can believe that animals closely resembling the Italian
greyhound, the bloodhound, the bull-dog, or Blenheim spaniel, &c. so unlike all wild
Canidae ever existed freely in a state of nature? It has often been loosely said that all
our races of dogs have been produced by the crossing of a few aboriginal species; but by
crossing we can get only forms in some degree intermediate between their parents; and if
we account for our several domestic races by this process, we must admit the former
existence of the most extreme forms, as the Italian greyhound, bloodhound, bull-dog,
&c., in the wild state. Moreover, the possibility of making distinct races by crossing
has been greatly exaggerated. There can be no doubt that a race may be modified by
occasional crosses, if aided by the careful selection of those individual mongrels, which
present any desired character; but that a race could be obtained nearly intermediate
between two extremely different races or species, I can hardly believe. Sir J. Sebright
expressly experimentised for this object, and failed. The offspring from the first cross
between two pure breeds is tolerably and sometimes (as I have found with pigeons)
extremely uniform, and everything seems simple enough; but when these mongrels are crossed
one with another for several generations, hardly two of them will be alike, and then the
extreme difficulty, or rather utter hopelessness, of the task becomes apparent. Certainly,
a breed intermediate between two very distinct breeds could not be got without
extreme care and long-continued selection; nor can I find a single case on record of a
permanent race having been thus formed.
On the Breeds of the Domestic pigeon.
Believing that it is always best to study some special group, I have, after
deliberation, taken up domestic pigeons. I have kept every breed which I could purchase or
obtain, and have been most kindly favoured with skins from several quarters of the world,
more especially by the Hon. W. Elliot from India, and by the Hon. C. Murray from Persia.
Many treatises in different languages have been published on pigeons, and some of them are
very important, as being of considerably antiquity. I have associated with several eminent
fanciers, and have been permitted to join two of the London Pigeon Clubs. The diversity of
the breeds is something astonishing. Compare the English carrier and the short-faced
tumbler, and see the wonderful difference in their beaks, entailing corresponding
differences in their skulls. The carrier, more especially the male bird, is also
remarkable from the wonderful development of the carunculated skin about the head, and
this is accompanied by greatly elongated eyelids, very large external orifices to the
nostrils, and a wide gape of mouth. The short-faced tumbler has a beak in outline almost
like that of a finch; and the common tumbler has the singular and strictly inherited habit
of flying at a great height in a compact flock, and tumbling in the air head over heels.
The runt is a bird of great size, with long, massive beak and large feet; some of the
sub-breeds of runts have very long necks, others very long wings and tails, others
singularly short tails. The barb is allied to the carrier, but, instead of a very long
beak, has a very short and very broad one. The pouter has a much elongated body, wings,
and legs; and its enormously developed crop, which it glories in inflating, may well
excite astonishment and even laughter. The turbit has a very short and conical beak, with
a line of reversed feathers down the breast; and it has the habit of continually expanding
slightly the upper part of the oesophagus. The Jacobin has the feathers so much reversed
along the back of the neck that they form a hood, and it has, proportionally to its size,
much elongated wing and tail feathers. The trumpeter and laugher, as their names express,
utter a very different coo from the other breeds. The fantail has thirty or even forty
tail-feathers, instead of twelve or fourteen, the normal number in all members of the
great pigeon family; and these feathers are kept expanded, and are carried so erect that
in good birds the head and tail touch; the oil-gland is quite aborted. Several other less
distinct breeds might have been specified.
In the skeletons of the several breeds, the development of the bones of the face in
length and breadth and curvature differs enormously. The shape, as well as the breadth and
length of the ramus of the lower jaw, varies in a highly remarkable manner. The number of
the caudal and sacral vertebrae vary; as does the number of the ribs, together with their
relative breadth and the presence of processes. The size and shape of the apertures in the
sternum are highly variable; so is the degree of divergence and relative size of the two
arms of the furcula. The proportional width of the gape of mouth, the proportional length
of the eyelids, of the orifice of the nostrils, of the tongue (not always in strict
correlation with the length of beak), the size of the crop and of the upper part of the
oesophagus; the development and abortion of the oil-gland; the number of the primary wing
and caudal feathers; the relative length of wing and tail to each other and to the body;
the relative length of leg and of the feet; the number of scutellae on the toes, the
development of skin between the toes, are all points of structure which are variable. The
period at which the perfect plumage is acquired varies, as does the state of the down with
which the nestling birds are clothed when hatched. The shape and size of the eggs vary.
The manner of flight differs remarkably; as does in some breeds the voice and disposition.
Lastly, in certain breeds, the males and females have come to differ to a slight degree
from each other.
Altogether at least a score of pigeons might be chosen, which if shown to an
ornithologist, and he were told that they were wild birds, would certainly, I think, be
ranked by him as well-defined species. Moreover, I do not believe that any ornithologist
would place the English carrier, the short-faced tumbler, the runt, the barb, pouter, and
fantail in the same genus; more especially as in each of these breeds several
truly-inherited sub-breeds, or species as he might have called them, could be shown him.
Great as the differences are between the breeds of pigeons, I am fully convinced that
the common opinion of naturalists is correct, namely, that all have descended from the
rock-pigeon (Columba livia), including under this term several geographical races or
sub-species, which differ from each other in the most trifling respects. As several of the
reasons which have led me to this belief are in some degree applicable in other cases, I
will here briefly give them. If the several breeds are not varieties, and have not
proceeded from the rock-pigeon, they must have descended from at least seven or eight
aboriginal stocks; for it is impossible to make the present domestic breeds by the
crossing of any lesser number: how, for instance, could a pouter be produced by crossing
two breeds unless one of the parent-stocks possessed the characteristic enormous crop? The
supposed aboriginal stocks must all have been rock-pigeons, that is, not breeding or
willingly perching on trees. But besides C. livia, with its geographical sub-species, only
two or three other species of rock-pigeons are known; and these have not any of the
characters of the domestic breeds. Hence the supposed aboriginal stocks must either still
exist in the countries where they were originally domesticated, and yet be unknown to
ornithologists; and this, considering their size, habits, and remarkable characters, seems
very improbable; or they must have become extinct in the wild state. But birds breeding on
precipices, and good fliers, are unlikely to be exterminated; and the common rock-pigeon,
which has the same habits with the domestic breeds, has not been exterminated even on
several of the smaller British islets, or on the shores of the Mediterranean. Hence the
supposed extermination of so many species having similar habits with the rock-pigeon seems
to me a very rash assumption. Moreover, the several above-named domesticated breeds have
been transported to all parts of the world, and, therefore, some of them must have been
carried back again into their native country; but not one has ever become wild or feral,
though the dovecot-pigeon, which is the rock-pigeon in a very slightly altered state, has
become feral in several places. Again, all recent experience shows that it is most
difficult to get any wild animal to breed freely under domestication; yet on the
hypothesis of the multiple origin of our pigeons, it must be assumed that at least seven
or eight species were so thoroughly domesticated in ancient times by half-civilized man,
as to be quite prolific under confinement.
An argument, as it seems to me, of great weight, and applicable in several other cases,
is, that the above-specified breeds, though agreeing generally in constitution, habits,
voice, colouring, and in most parts of their structure, with the wild rock-pigeon, yet are
certainly highly abnormal in other parts of their structure: we may look in vain
throughout the whole great family of Columbidae for a beak like that of the English
carrier, or that of the short-faced tumbler, or barb; for reversed feathers like those of
the jacobin; for a crop like that of the pouter; for tail-feathers like those of the
fantail. Hence it must be assumed not only that half-civilized man succeeded in thoroughly
domesticating several species, but that he intentionally or by chance picked out
extraordinarily abnormal species; and further, that these very species have since all
become extinct or unknown. So many strange contingencies seem to me improbable in the
highest degree.
Some facts in regard to the colouring of pigeons well deserve consideration. The
rock-pigeon is of a slaty-blue, and has a white rump (the Indian sub-species, C.
intermedia of Strickland, having it bluish); the tail has a terminal dark bar, with the
bases of the outer feathers externally edged with white; the wings have two black bars:
some semi-domestic breeds and some apparently truly wild breeds have, besides the two
black bars, the wings chequered with black. These several marks do not occur together in
any other species of the whole family. Now, in every one of the domestic breeds, taking
thoroughly well-bred birds, all the above marks, even to the white edging of the outer
tail-feathers, sometimes concur perfectly developed. Moreover, when two birds belonging to
two distinct breeds are crossed, neither of which is blue or has any of the
above-specified marks, the mongrel offspring are very apt suddenly to acquire these
characters; for instance, I crossed some uniformly white fantails with some uniformly
black barbs, and they produced mottled brown and black birds; these I again crossed
together, and one grandchild of the pure white fantail and pure black barb was of as
beautiful a blue colour, with the white rump, double black wing-bar, and barred and
white-edged tail-feathers, as any wild rock-pigeon! We can understand these facts, on the
well-known principle of reversion to ancestral characters, if all the domestic breeds have
descended from the rock-pigeon. But if we deny this, we must make one of the two following
highly improbable suppositions. Either, firstly, that all the several imagined aboriginal
stocks were coloured and marked like the rock-pigeon, although no other existing species
is thus coloured and marked, so that in each separate breed there might be a tendency to
revert to the very same colours and markings. Or, secondly, that each breed, even the
purest, has within a dozen or, at most, within a score of generations, been crossed by the
rock-pigeon: I say within a dozen or twenty generations, for we know of no fact
countenancing the belief that the child ever reverts to some one ancestor, removed by a
greater number of generations. In a breed which has been crossed only once with some
distinct breed, the tendency to reversion to any character derived from such cross will
naturally become less and less, as in each succeeding generation there will be less of the
foreign blood; but when there has been no cross with a distinct breed, and there is a
tendency in both parents to revert to a character, which has been lost during some former
generation, this tendency, for all that we can see to the contrary, may be transmitted
undiminished for an indefinite number of generations. These two distinct cases are often
confounded in treatises on inheritance.
Lastly, the hybrids or mongrels from between all the domestic breeds of pigeons are
perfectly fertile. I can state this from my own observations, purposely made on the most
distinct breeds. Now, it is difficult, perhaps impossible, to bring forward one case of
the hybrid offspring of two animals clearly distinct being themselves perfectly
fertile. Some authors believe that long-continued domestication eliminates this strong
tendency to sterility: from the history of the dog I think there is some probability in
this hypothesis, if applied to species closely related together, though it is unsupported
by a single experiment. But to extend the hypothesis so far as to suppose that species,
aboriginally as distinct as carriers, tumblers, pouters, and fantails now are, should
yield offspring perfectly fertile, inter se, seems to me rash in the extreme.
From these several reasons, namely, the improbability of man having formerly got seven
or eight supposed species of pigeons to breed freely under domestication; these supposed
species being quite unknown in a wild state, and their becoming nowhere feral; these
species having very abnormal characters in certain respects, as compared with all other
Columbidae, though so like in most other respects to the rock-pigeon; the blue colour and
various marks occasionally appearing in all the breeds, both when kept pure and when
crossed; the mongrel offspring being perfectly fertile; from these several reasons, taken
together, I can feel no doubt that all our domestic breeds have descended from the Columba
livia with its geographical sub-species.
In favour of this view, I may add, firstly, that C. livia, or the rock-pigeon, has been
found capable of domestication in Europe and in India; and that it agrees in habits and in
a great number of points of structure with all the domestic breeds. Secondly, although an
English carrier or short-faced tumbler differs immensely in certain characters from the
rock-pigeon, yet by comparing the several sub-breeds of these breeds, more especially
those brought from distant countries, we can make an almost perfect series between the
extremes of structure. Thirdly, those characters which are mainly distinctive of each
breed, for instance the wattle and length of beak of the carrier, the shortness of that of
the tumbler, and the number of tail-feathers in the fantail, are in each breed eminently
variable; and the explanation of this fact will be obvious when we come to treat of
selection. Fourthly, pigeons have been watched, and tended with the utmost care, and loved
by many people. They have been domesticated for thousands of years in several quarters of
the world; the earliest known record of pigeons is in the fifth Aegyptian dynasty, about
3000 B.C., as was pointed out to me by Professor Lepsius; but Mr Birch informs me that
pigeons are given in a bill of fare in the previous dynasty. In the time of the Romans, as
we hear from Pliny, immense prices were given for pigeons; 'nay, they are come to this
pass, that they can reckon up their pedigree and race.' Pigeons were much valued by Akber
Khan in India, about the year 1600; never less than 20,000 pigeons were taken with the
court. 'The monarchs of Iran and Turan sent him some very rare birds;' and, continues the
courtly historian, 'His Majesty by crossing the breeds, which method was never practised
before, has improved them astonishingly.' About this same period the Dutch were as eager
about pigeons as were the old Romans. The paramount importance of these considerations in
explaining the immense amount of variation which pigeons have undergone, will be obvious
when we treat of Selection. We shall then, also, see how it is that the breeds so often
have a somewhat monstrous character. It is also a most favourable circumstance for the
production of distinct breeds, that male and female pigeons can be easily mated for life;
and thus different breeds can be kept together in the same aviary.
I have discussed the probable origin of domestic pigeons at some, yet quite
insufficient, length; because when I first kept pigeons and watched the several kinds,
knowing well how true they bred, I felt fully as much difficulty in believing that they
could ever have descended from a common parent, as any naturalist could in coming to a
similar conclusion in regard to the many species of finches, or other large groups of
birds, in nature. One circumstance has struck me much; namely, that all the breeders of
the various domestic animals and the cultivators of plants, with whom I have ever
conversed, or whose treatises I have read, are firmly convinced that the several breeds to
which each has attended, are descended from so many aboriginally distinct species. Ask, as
I have asked, a celebrated raiser of Hereford cattle, whether his cattle might not have
descended from long horns, and he will laugh you to scorn. I have never met a pigeon, or
poultry, or duck, or rabbit fancier, who was not fully convinced that each main breed was
descended from a distinct species. Van Mons, in his treatise on pears and apples, shows
how utterly he disbelieves that the several sorts, for instance a Ribston-pippin or
Codlin-apple, could ever have proceeded from the seeds of the same tree. Innumerable other
examples could be given. The explanation, I think, is simple: from long-continued study
they are strongly impressed with the differences between the several races; and though
they well know that each race varies slightly, for they win their prizes by selecting such
slight differences, yet they ignore all general arguments, and refuse to sum up in their
minds slight differences accumulated during many successive generations. May not those
naturalists who, knowing far less of the laws of inheritance than does the breeder, and
knowing no more than he does of the intermediate links in the long lines of descent, yet
admit that many of our domestic races have descended from the same parents may they not
learn a lesson of caution, when they deride the idea of species in a state of nature being
lineal descendants of other species?
Selection
Let us now briefly consider the steps by which domestic races have been produced,
either from one or from several allied species. Some little effect may, perhaps, be
attributed to the direct action of the external conditions of life, and some little to
habit; but he would be a bold man who would account by such agencies for the differences
of a dray and race horse, a greyhound and bloodhound, a carrier and tumbler pigeon. One of
the most remarkable features in our domesticated races is that we see in them adaptation,
not indeed to the animal's or plant's own good, but to man's use or fancy. Some variations
useful to him have probably arisen suddenly, or by one step; many botanists, for instance,
believe that the fuller's teazle, with its hooks, which cannot be rivalled by any
mechanical contrivance, is only a variety of the wild Dipsacus; and this amount of change
may have suddenly arisen in a seedling. So it has probably been with the turnspit dog; and
this is known to have been the case with the ancon sheep. But when we compare the
dray-horse and race-horse, the dromedary and camel, the various breeds of sheep fitted
either for cultivated land or mountain pasture, with the wool of one breed good for one
purpose, and that of another breed for another purpose; when we compare the many breeds of
dogs, each good for man in very different ways; when we compare the gamecock, so
pertinacious in battle, with other breeds so little quarrelsome, with 'everlasting layers'
which never desire to sit, and with the bantam so small and elegant; when we compare the
host of agricultural, culinary, orchard, and flower-garden races of plants, most useful to
man at different seasons and for different purposes, or so beautiful in his eyes, we must,
I think, look further than to mere variability. We cannot suppose that all the breeds were
suddenly produced as perfect and as useful as we now see them; indeed, in several cases,
we know that this has not been their history. The key is man's power of accumulative
selection: nature gives successive variations; man adds them up in certain directions
useful to him. In this sense he may be said to make for himself useful breeds.
The great power of this principle of selection is not hypothetical. It is certain that
several of our eminent breeders have, even within a single lifetime, modified to a large
extent some breeds of cattle and sheep. In order fully to realise what they have done, it
is almost necessary to read several of the many treatises devoted to this subject, and to
inspect the animals. Breeders habitually speak of an animal's organisation as something
quite plastic, which they can model almost as they please. If I had space I could quote
numerous passages to this effect from highly competent authorities. Youatt, who was
probably better acquainted with the works of agriculturalists than almost any other
individual, and who was himself a very good judge of an animal, speaks of the principle of
selection as 'that which enables the agriculturist, not only to modify the character of
his flock, but to change it altogether. It is the magician's wand, by means of which he
may summon into life whatever form and mould he pleases.' Lord Somerville, speaking of
what breeders have done for sheep, says: 'It would seem as if they had chalked out upon a
wall a form perfect in itself, and then had given it existence.' That most skilful
breeder, Sir John Sebright, used to say, with respect to pigeons, that 'he would produce
any given feather in three years, but it would take him six years to obtain head and
beak.' In Saxony the importance of the principle of selection in regard to merino sheep is
so fully recognised, that men follow it as a trade: the sheep are placed on a table and
are studied, like a picture by a connoisseur; this is done three times at intervals of
months, and the sheep are each time marked and classed, so that the very best may
ultimately be selected for breeding.
What English breeders have actually effected is proved by the enormous prices given for
animals with a good pedigree; and these have now been exported to almost every quarter of
the world. The improvement is by no means generally due to crossing different breeds; all
the best breeders are strongly opposed to this practice, except sometimes amongst closely
allied sub-breeds. And when a cross has been made, the closest selection is far more
indispensable even than in ordinary cases. If selection consisted merely in separating
some very distinct variety, and breeding from it, the principle would be so obvious as
hardly to be worth notice; but its importance consists in the great effect produced by the
accumulation in one direction, during successive generations, of differences absolutely
inappreciable by an uneducated eye differences which I for one have vainly attempted to
appreciate. Not one man in a thousand has accuracy of eye and judgement sufficient to
become an eminent breeder. If gifted with these qualities, and he studies his subject for
years, and devotes his lifetime to it with indomitable perseverance, he will succeed, and
may make great improvements; if he wants any of these qualities, he will assuredly fail.
Few would readily believe in the natural capacity and years of practice requisite to
become even a skilful pigeon-fancier.
The same principles are followed by horticulturists; but the variations are here often
more abrupt. No one supposes that our choicest productions have been produced by a single
variation from the aboriginal stock. We have proofs that this is not so in some cases, in
which exact records have been kept; thus, to give a very trifling instance, the
steadily-increasing size of the common gooseberry may be quoted. We see an astonishing
improvement in many florists' flowers, when the flowers of the present day are compared
with drawings made only twenty or thirty years ago. When a race of plants is once pretty
well established, the seed-raisers do not pick out the best plants, but merely go over
their seed-beds, and pull up the 'rogues,' as they call the plants that deviate from the
proper standard. With animals this kind of selection is, in fact, also followed; for
hardly any one is so careless as to allow his worst animals to breed.
In regard to plants, there is another means of observing the accumulated effects of
selection namely, by comparing the diversity of flowers in the different varieties of the
same species in the flower-garden; the diversity of leaves, pods, or tubers, or whatever
part is valued, in the kitchen-garden, in comparison with the flowers of the same
varieties; and the diversity of fruit of the same species in the orchard, in comparison
with the leaves and flowers of the same set of varieties. See how different the leaves of
the cabbage are, and how extremely alike the flowers; how unlike the flowers of the
heartsease are, and how alike the leaves; how much the fruit of the different kinds of
gooseberries differ in size, colour, shape, and hairiness, and yet the flowers present
very slight differences. It is not that the varieties which differ largely in some one
point do not differ at all in other points; this is hardly ever, perhaps never, the case.
The laws of correlation of growth, the importance of which should never be overlooked,
will ensure some differences; but, as a general rule, I cannot doubt that the continued
selection of slight variations, either in the leaves, the flowers, or the fruit, will
produce races differing from each other chiefly in these characters.
It may be objected that the principle of selection has been reduced to methodical
practice for scarcely more than three-quarters of a century; it has certainly been more
attended to of late years, and many treatises have been published on the subject; and the
result, I may add, has been, in a corresponding degree, rapid and important. But it is
very far from true that the principle is a modern discovery. I could give several
references to the full acknowledgement of the importance of the principle in works of high
antiquity. In rude and barbarous periods of English history choice animals were often
imported, and laws were passed to prevent their exportation: the destruction of horses
under a certain size was ordered, and this may be compared to the 'roguing' of plants by
nurserymen. The principle of selection I find distinctly given in an ancient Chinese
encyclopaedia. Explicit rules are laid down by some of the Roman classical writers. From
passages in Genesis, it is clear that the colour of domestic animals was at that early
period attended to. Savages now sometimes cross their dogs with wild canine animals, to
improve the breed, and they formerly did so, as is attested by passages in Pliny. The
savages in South Africa match their draught cattle by colour, as do some of the Esquimaux
their teams of dogs. Livingstone shows how much good domestic breeds are valued by the
negroes of the interior of Africa who have not associated with Europeans. Some of these
facts do not show actual selection, but they show that the breeding of domestic animals
was carefully attended to in ancient times, and is now attended to by the lowest savages.
It would, indeed, have been a strange fact, had attention not been paid to breeding, for
the inheritance of good and bad qualities is so obvious.
At the present time, eminent breeders try by methodical selection, with a distinct
object in view, to make a new strain or sub-breed, superior to anything existing in the
country. But, for our purpose, a kind of Selection, which may be called Unconscious, and
which results from every one trying to possess and breed from the best individual animals,
is more important. Thus, a man who intends keeping pointers naturally tries to get as good
dogs as he can, and afterwards breeds from his own best dogs, but he has no wish or
expectation of permanently altering the breed. Nevertheless I cannot doubt that this
process, continued during centuries, would improve and modify any breed, in the same way
as Bakewell, Collins, &c., by this very same process, only carried on more
methodically, did greatly modify, even during their own lifetimes, the forms and qualities
of their cattle. Slow and insensible changes of this kind could never be recognised unless
actual measurements or careful drawings of the breeds in question had been made long ago,
which might serve for comparison. In some cases, however, unchanged or but little changed
individuals of the same breed may be found in less civilised districts, where the breed
has been less improved. There is reason to believe that King Charles's spaniel has been
unconsciously modified to a large extent since the time of that monarch. Some highly
competent authorities are convinced that the setter is directly derived from the spaniel,
and has probably been slowly altered from it. It is known that the English pointer has
been greatly changed within the last century, and in this case the change has, it is
believed, been chiefly effected by crosses with the fox-hound; but what concerns us is,
that the change has been effected unconsciously and gradually, and yet so effectually,
that, though the old Spanish pointer certainly came from Spain, Mr Barrow has not seen, as
I am informed by him, any native dog in Spain like our pointer.
By a similar process of selection, and by careful training, the whole body of English
racehorses have come to surpass in fleetness and size the parent Arab stock, so that the
latter, by the regulations for the Goodwood Races, are favoured in the weights they carry.
Lord Spencer and others have shown how the cattle of England have increased in weight and
in early maturity, compared with the stock formerly kept in this country. By comparing the
accounts given in old pigeon treatises of carriers and tumblers with these breeds as now
existing in Britain, India, and Persia, we can, I think, clearly trace the stages through
which they have insensibly passed, and come to differ so greatly from the rock-pigeon.
Youatt gives an excellent illustration of the effects of a course of selection, which
may be considered as unconsciously followed, in so far that the breeders could never have
expected or even have wished to have produced the result which ensued namely, the
production of two distinct strains. The two flocks of Leicester sheep kept by Mr Buckley
and Mr Burgess, as Mr Youatt remarks, 'have been purely bred from the original stock of Mr
Bakewell for upwards of fifty years. There is not a suspicion existing in the mind of any
one at all acquainted with the subject that the owner of either of them has deviated in
any one instance from the pure blood of Mr Bakewell's flock, and yet the difference
between the sheep possessed by these two gentlemen is so great that they have the
appearance of being quite different varieties.'
If there exist savages so barbarous as never to think of the inherited character of the
offspring of their domestic animals, yet any one animal particularly useful to them, for
any special purpose, would be carefully preserved during famines and other accidents, to
which savages are so liable, and such choice animals would thus generally leave more
offspring than the inferior ones; so that in this case there would be a kind of
unconscious selection going on. We see the value set on animals even by the barbarians of
Tierra del Fuego, by their killing and devouring their old women, in times of dearth, as
of less value than their dogs.
In plants the same gradual process of improvement, through the occasional preservation
of the best individuals, whether or not sufficiently distinct to be ranked at their first
appearance as distinct varieties, and whether or not two or more species or races have
become blended together by crossing, may plainly be recognised in the increased size and
beauty which we now see in the varieties of the heartsease, rose, pelargonium, dahlia, and
other plants, when compared with the older varieties or with their parent-stocks. No one
would ever expect to get a first-rate heartsease or dahlia from the seed of a wild plant.
No one would expect to raise a first-rate melting pear from the seed of a wild pear,
though he might succeed from a poor seedling growing wild, if it had come from a
garden-stock. The pear, though cultivated in classical times, appears, from Pliny's
description, to have been a fruit of very inferior quality. I have seen great surprise
expressed in horticultural works at the wonderful skill of gardeners, in having produced
such splendid results from such poor materials; but the art, I cannot doubt, has been
simple, and, as far as the final result is concerned, has been followed almost
unconsciously. It has consisted in always cultivating the best known variety, sowing its
seeds, and, when a slightly better variety has chanced to appear, selecting it, and so
onwards. But the gardeners of the classical period, who cultivated the best pear they
could procure, never thought what splendid fruit we should eat; though we owe our
excellent fruit, in some small degree, to their having naturally chosen and preserved the
best varieties they could anywhere find.
A large amount of change in our cultivated plants, thus slowly and unconsciously
accumulated, explains, as I believe, the well-known fact, that in a vast number of cases
we cannot recognise, and therefore do not know, the wild parent-stocks of the plants which
have been longest cultivated in our flower and kitchen gardens. If it has taken centuries
or thousands of years to improve or modify most of our plants up to their present standard
of usefulness to man, we can understand how it is that neither Australia, the Cape of Good
Hope, nor any other region inhabited by quite uncivilised man, has afforded us a single
plant worth culture. It is not that these countries, so rich in species, do not by a
strange chance possess the aboriginal stocks of any useful plants, but that the native
plants have not been improved by continued selection up to a standard of perfection
comparable with that given to the plants in countries anciently civilised.
In regard to the domestic animals kept by uncivilised man, it should not be overlooked
that they almost always have to struggle for their own food, at least during certain
seasons. And in two countries very differently circumstanced, individuals of the same
species, having slightly different constitutions or structure, would often succeed better
in the one country than in the other, and thus by a process of 'natural selection,' as
will hereafter be more fully explained, two sub-breeds might be formed. This, perhaps,
partly explains what has been remarked by some authors, namely, that the varieties kept by
savages have more of the character of species than the varieties kept in civilised
countries.
On the view here given of the all-important part which selection by man has played, it
becomes at once obvious, how it is that our domestic races show adaptation in their
structure or in their habits to man's wants or fancies. We can, I think, further
understand the frequently abnormal character of our domestic races, and likewise their
differences being so great in external characters and relatively so slight in internal
parts or organs. Man can hardly select, or only with much difficulty, any deviation of
structure excepting such as is externally visible; and indeed he rarely cares for what is
internal. He can never act by selection, excepting on variations which are first given to
him in some slight degree by nature. No man would ever try to make a fantail, till he saw
a pigeon with a tail developed in some slight degree in an unusual manner, or a pouter
till he saw a pigeon with a crop of somewhat unusual size; and the more abnormal or
unusual any character was when it first appeared, the more likely it would be to catch his
attention. But to use such an expression as trying to make a fantail, is, I have no doubt,
in most cases, utterly incorrect. The man who first selected a pigeon with a slightly
larger tail, never dreamed what the descendants of that pigeon would become through
long-continued, partly unconscious and partly methodical selection. Perhaps the parent
bird of all fantails had only fourteen tail-feathers somewhat expanded, like the present
Java fantail, or like individuals of other and distinct breeds, in which as many as
seventeen tail-feathers have been counted. Perhaps the first pouter-pigeon did not inflate
its crop much more than the turbit now does the upper part of its oesophagus, a habit
which is disregarded by all fanciers, as it is not one of the points of the breed.
Nor let it be thought that some great deviation of structure would be necessary to
catch the fancier's eye: he perceives extremely small differences, and it is in human
nature to value any novelty, however slight, in one's own possession. Nor must the value
which would formerly be set on any slight differences in the individuals of the same
species, be judged of by the value which would now be set on them, after several breeds
have once fairly been established. Many slight differences might, and indeed do now, arise
amongst pigeons, which are rejected as faults or deviations from the standard of
perfection of each breed. The common goose has not given rise to any marked varieties;
hence the Thoulouse and the common breed, which differ only in colour, that most fleeting
of characters, have lately been exhibited as distinct at our poultry-shows.
I think these views further explain what has sometimes been noticed namely that we know
nothing about the origin or history of any of our domestic breeds. But, in fact, a breed,
like a dialect of a language, can hardly be said to have had a definite origin. A man
preserves and breeds from an individual with some slight deviation of structure, or takes
more care than usual in matching his best animals and thus improves them, and the improved
individuals slowly spread in the immediate neighbourhood. But as yet they will hardly have
a distinct name, and from being only slightly valued, their history will be disregarded.
When further improved by the same slow and gradual process, they will spread more widely,
and will get recognised as something distinct and valuable, and will then probably first
receive a provincial name. In semi-civilised countries, with little free communication,
the spreading and knowledge of any new sub-breed will be a slow process. As soon as the
points of value of the new sub-breed are once fully acknowledged, the principle, as I have
called it, of unconscious selection will always tend, perhaps more at one period than at
another, as the breed rises or falls in fashion, perhaps more in one district than in
another, according to the state of civilisation of the inhabitants slowly to add to the
characteristic features of the breed, whatever they may be. But the chance will be
infinitely small of any record having been preserved of such slow, varying, and insensible
changes.
I must now say a few words on the circumstances, favourable, or the reverse, to man's
power of selection. A high degree of variability is obviously favourable, as freely giving
the materials for selection to work on; not that mere individual differences are not amply
sufficient, with extreme care, to allow of the accumulation of a large amount of
modification in almost any desired direction. But as variations manifestly useful or
pleasing to man appear only occasionally, the chance of their appearance will be much
increased by a large number of individuals being kept; and hence this comes to be of the
highest importance to success. On this principle Marshall has remarked, with respect to
the sheep of parts of Yorkshire, that 'as they generally belong to poor people, and are
mostly in small lots, they never can be improved.' On the other hand, nurserymen,
from raising large stocks of the same plants, are generally far more successful than
amateurs in getting new and valuable varieties. The keeping of a large number of
individuals of a species in any country requires that the species should be placed under
favourable conditions of life, so as to breed freely in that country. When the individuals
of any species are scanty, all the individuals, whatever their quality may be, will
generally be allowed to breed, and this will effectually prevent selection. But probably
the most important point of all, is, that the animal or plant should be so highly useful
to man, or so much valued by him, that the closest attention should be paid to even the
slightest deviation in the qualities or structure of each individual. Unless such
attention be paid nothing can be effected. I have seen it gravely remarked, that it was
most fortunate that the strawberry began to vary just when gardeners began to attend
closely to this plant. No doubt the strawberry had always varied since it was cultivated,
but the slight varieties had been neglected. As soon, however, as gardeners picked out
individual plants with slightly larger, earlier, or better fruit, and raised seedlings
from them, and again picked out the best seedlings and bred from them, then, there
appeared (aided by some crossing with distinct species) those many admirable varieties of
the strawberry which have been raised during the last thirty or forty years.
In the case of animals with separate sexes, facility in preventing crosses is an
important element of success in the formation of new races, at least, in a country which
is already stocked with other races. In this respect enclosure of the land plays a part.
Wandering savages or the inhabitants of open plains rarely possess more than one breed of
the same species. Pigeons can be mated for life, and this is a great convenience to the
fancier, for thus many races may be kept true, though mingled in the same aviary; and this
circumstance must have largely favoured the improvement and formation of new breeds.
Pigeons, I may add, can be propagated in great numbers and at a very quick rate, and
inferior birds may be freely rejected, as when killed they serve for food. On the other
hand, cats, from their nocturnal rambling habits, cannot be matched, and, although so much
valued by women and children, we hardly ever see a distinct breed kept up; such breeds as
we do sometimes see are almost always imported from some other country, often from
islands. Although I do not doubt that some domestic animals vary less than others, yet the
rarity or absence of distinct breeds of the cat, the donkey, peacock, goose, &c., may
be attributed in main part to selection not having been brought into play: in cats, from
the difficulty in pairing them; in donkeys, from only a few being kept by poor people, and
little attention paid to their breeding; in peacocks, from not being very easily reared
and a large stock not kept; in geese, from being valuable only for two purposes, food and
feathers, and more especially from no pleasure having been felt in the display of distinct
breeds.
To sum up on the origin of our Domestic Races of animals and plants. I
believe that the conditions of life, from their action on the reproductive system, are so
far of the highest importance as causing variability. I do not believe that variability is
an inherent and necessary contingency, under all circumstances, with all organic beings,
as some authors have thought. The effects of variability are modified by various degrees
of inheritance and of reversion. Variability is governed by many unknown laws, more
especially by that of correlation of growth. Something may be attributed to the direct
action of the conditions of life. Something must be attributed to use and disuse. The
final result is thus rendered infinitely complex. In some cases, I do not doubt that the
intercrossing of species, aboriginally distinct, has played an important part in the
origin of our domestic productions. When in any country several domestic breeds have once
been established, their occasional intercrossing, with the aid of selection, has, no
doubt, largely aided in the formation of new sub-breeds; but the importance of the
crossing of varieties has, I believe, been greatly exaggerated, both in regard to animals
and to those plants which are propagated by seed. In plants which are temporarily
propagated by cuttings, buds, &c., the importance of the crossing both of distinct
species and of varieties is immense; for the cultivator here quite disregards the extreme
variability both of hybrids and mongrels, and the frequent sterility of hybrids; but the
cases of plants not propagated by seed are of little importance to us, for their endurance
is only temporary. Over all these causes of Change I am convinced that the accumulative
action of Selection, whether applied methodically and more quickly, or unconsciously and
more slowly, but more efficiently, is by far the predominant power.