 Chapter
1 - Variation Under Domestication
*
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.
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