Chapter I Variation under
Domestication
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.
2 It has been disputed at what period of life 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 organisation, 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.
3 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.
4 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.
5 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.
6 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.
7 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.
8 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 organisation seems to have become plastic, and tends to
depart in some small degree from that of the parental type.
9 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.
10 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.
11 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.
12 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.
13 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 it 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.
14 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 rein-deer, 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.
15 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?
16 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.
17 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.
18 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.
19 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.
20 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.
21 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.
22 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.
23 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.
24 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.
25 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.
26 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.
27 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?
28 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 game-cock, 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.
29 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.
30 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
judgment 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.
31 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.
32 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.
33 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 acknowledgment 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.
34 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. Borrow has not seen, as I am informed by him, any native dog
in Spain like our pointer.
35 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.
36 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.'
37 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.
38 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.
39 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.
40 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.
41 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.
42 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.
43 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.
44 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.
45 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.
46 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.