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lated variation, the importance of which should never be overlooked, will
insure some differences; but, as a general rule, it cannot be doubted 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

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 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 works of high
antiquity, in which the full importance of the principle is acknowledged. 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 dis-
tinctly 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 color 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 color, as
do some of the Esquimaux their team of dogs. Livingstone states that good
domestic breeds are highly valued by the negroes in 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 any-
thing of the kind in the country. But, for our purpose, a form 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 we may infer
that this process, continued during centuries, would improve and modify
any breed, in the same way as Bakewell, Collins, etc., by this very same
process, only carried on more methodically, did greatly modify, even during
their lifetimes, the forms and qualities of their cattle. Slow and insensible
changes of this kind can never be recognized unless actual measurements or
careful drawings of the breeds in question have been made long ago, which
may serve for comparison. In some cases, however, unchanged, or but little
changed, individuals of the same breed exist in less civilized districts, where
the breed has been less improved. There is reason to believe that King
Charles' 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 eff"ected by crosses with the foxhound; but what con-
cerns us is, that the change has been effected unconsciously and gradually,
and yet so eff"ectually 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.

By a similar process of selection, and by careful training, English race-
horses have come to surpass in fleetness and size the parent Arabs, so that
the latter, by the regulations for the Goodwood Races, are favored in the
weights which 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 various old treatises of the former and present state of carrier and
tumbler pigeons in Britain, India, and Persia, we can trace the stages
through which they have insensibly passed, and come to diff'er so greatly
from the rock-pigeon.

Youatt gives an excellent illustration of the effects of a course of selection
which may be considered as unconscious, in so far that the breeders could
never have expected or even wished, to produce the result which ensued —
namely, the production of the distinct strains. 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 upward 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 pre-
served during famines and other accidents, to which savages are so liable,
and such choice animals would thus generally leave more off"spring 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 recognized in the increased size and beauty which we now see
in the varieties of the heart's-ease, 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 heart's-ease or dahlia from the
seed of a wild plant. No one would expect to raise a first-rate melting pear
from the seed of the 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 horti-
cultural works at the wonderful skill of gardeners in having produced such
splendid results from such poor materials ; but the art 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 chanced to appear, selecting it,
and so onward. But the gardeners of the classical period, who cultivated the
best pears which 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 any-
where find.

A large amount of change, thus slowly and unconsciously accumulated,
explains, as I believe, the well-known fact, that in a number of cases we
cannot recognize, 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 under-
stand how it is that neither Australia, the Gape of Good Hope, nor any
other region inhabited by quite uncivilized 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 acquired by the plants in
countries anciently civilized.

In regard to the domestic animals kept by uncivilized 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 circum-
stanced, individuals of the same species, having slightly different constitu-
tions 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 why the varieties kept by savages, as has been remarked by some
authors, have more of the character of true species than the varieties kept
in civilized countries.

On the view here given of the 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 ex-
cepting 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 four-
teen 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 turbid 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 have been set on
any slight differences in the individuals of the same species, be judged of by
the value which is now set on them, after several breeds have fairly been
established. It is known that with pigeons many slight variations now occa-
sionally appear, but these are rejected as faults or deviations from the
standard of perfection in each breed. The common goose has not given rise
to any marked varieties; hence the Toulouse and the common breed, which
differ only in color, that most fleeting of characters, have lately been ex-
hibited as distinct at our poultry shows.

These views appear to explain what has sometimes been noticed, namely,
that w^e know hardly anything 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 a distinct 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 animals slowly spread in the immediate neighborhood. But they
will as yet hardly have a distinct name, and from being only slightly valued,
their history will have been disregarded. When further improved by the
same slow and gradual process, they will spread more widely, and will be
recognized as something distinct and valuable, and will then probably first
receive a provincial name. In semi-civilized countries, with little free com-
munication, the spreading of a new sub-breed would be a slow process. As
soon as the points of value are once 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 civilization of the
inhabitants — slowly to add to the characteristic features of the breed, what-
ever they may be. But the chance will be infinitely small of any record having
been preserved of such slow, varying, and insensible changes.



I will now say a few words on the circumstances, favorable or the reverse,
to man's power of selection. A high degree of variability is obviously
favorable, 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 in-
creased by a large number of individuals being kept. Hence, number is of
the highest importance for success. On this principle Marshall formerly re-
marked, with respect to the sheep of part of Yorkshire, "As they generally
belong to poor people, and are mostly iw small lots, they never can be im-
proved." On the other hand, nurserymen, from keeping large stocks of the
same plant, are generally far more successful than amateurs in raising new
and valuable varieties. A large number of individuals of an animal or plant
can be reared only where the conditions for its propagation are favorable.
When the individuals are scanty all will be allowed to breed, whatever their
quality may be, and this will effectually prevent selection. But probably the
most important element is that the animal or plant should be so highly
valued by man, that the closest attention is paid to even the slightest devia-
tions in its qualities or structure. 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 to this
plant. No doubt the strawberry had always varied since it was cultivated, but
the slight variations 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 (with some aid by crossing distinct species) those many
admirable varieties of the strawberry were raised which have appeared
during the last half-century.

With animals, facility in preventing crosses is an important element 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 con-
venience to the fancier, for thus many races may be improved and kept true,
though mingled in the same aviary; and this circumstance must have largely
fa\ ored the 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 easily matched, and, although
so much valued by women and children, we rarely see a distinct breed long
kept up; such breeds as we do sometimes see are almost always imported
from some other country. 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, etc., 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; for recently in certain parts of Spain
and of the United States this animal has been surprisingly modified and
improved by careful selection; in peacocks, from not being very easily reared
and a large stock not kept; in geese, from being valuable only for two pur-
poses, food and feathers, and more especially from no pleasure having been
felt in the display of distinct breeds; but the goose, under the conditions to
which it is exposed when domesticated, seems to have a singularly inflexible
organization, though it has varied to a slight extent, as I have elsewhere

Some authors have maintained that the amount of variation in our
domestic productions is soon reached, and can never afterward be exceeded.
It would be somewhat rash to assert that the limit has been attained in any
one case; for almost all our animals and plants have been greatly improved
in many ways within a recent period; and this implies variation. It would
be equally rash to assert that characters now increased to their utmost limit,
could not, after remaining fixed for many centuries, again vary under new
conditions of life. No doubt, as Mr. Wallace has remarked with much truth,
a limit will be at last reached. For instance, there must be a limit to the
fleetness of any terrestrial animal, as this will be determined by the friction
to be overcome, the weight of the body to be carried, and the power of con-
traction in the muscular fibres. But what concerns us is that the domestic
varieties of the same species differ from each other in almost every charac-
ter, which man has attended to and selected, more than do the distinct
species of the same genera. Isidore Geoffroy Saint-Hilaire has proved this in
regard to size, and so it is with color, and probably with the length of hair.
With respect to fleetness, which depends on many bodily characters. Eclipse
was far fleeter, and a dray-horse is comparably stronger, than any two natural
species belonging to the same genus. So with plants, the seeds of the different
varieties of the bean or maize probably differ more in size than do the seeds
of the distinct species in any one genus in the same two families. The same
remark holds good in regard to the fruit of the several varieties of the plum,
and still more strongly with the melon, as well as in many other analogous

To sum up on the origin of our domestic races of animals and plants.
Changed conditions of fife are of the highest importance in causing varia-
biHty, both by acting directly on the organization, and indirectly by affecting
the reproductive system. It is not probable that variability is an inherent and
necessary contingent, under all circumstances. The greater or less force of
inheritance and reversion determine whether variations shall endure. Varia-
bility is governed by many unknown laws, of which correlated growth is
probably the most important. Something, but how much we do not know,
may be attributed to the definite action of the conditions of life. Some, per-


haps a great, effect may be attributed to the increased use or disuse of parts.
The final result is thus rendered infinitely complex. In some cases the inter-
crossing of aboriginally distinct species appears to have played an important
part in the origin of our breeds. When several breeds have once been formed
in any country, their occasional intercrossing, with the aid of selection, has,
no doubt, largely aided in the formation of new sub-breeds; but the impor-
tance of crossing has been much exaggerated, both in regard to animals and
to those plants which are propagated by seed. With plants which are tem-
porarily propagated by cuttings, buds, etc., the importance of crossing is
immense ; for the cultivator may here disregard the extreme variability both
of hybrids and of mongrels, and the sterility of hybrids; but plants not
propagated by seed are of little importance to us, for their endurance is
only temporary. Over all these causes of change, the accumulative action of
selection, whether applied methodically and quickly, or unconsciously and
slowly, but more efficiently, seems to have been the predominant power.


Variation Under Nature

Variability — Individual Differences — ^Doubtful Species — Wide ranging, much diffused,
and common Species, vary most — Species of the Larger Genera in each Country
vary more frequently than the Species of the Smaller Genera — Many of the
Species of the Larger Genera resemble Varieties in being very closely, but un-
equally, related to each other, and in having Restricted Ranges.

Before applying the principles arrived at in the last chapter to organic
beings in a state of nature, we must briefly discuss whether these latter are
subject to any variation. To treat this subject properly, a long catalogue of
dry facts ought to be given; but these I shall reserve for a future work. Nor
shall I here discuss the various definitions which have been given of the term
species. No one definition has satisfied all naturalists; yet every naturalist
knows vaguely what he means when he speaks of a species. Generally the
term includes the unknown element of a distinct act of creation. The term
"variety" is almost equally difficult to define; but here community of descent
is almost universally implied, though it can rarely be proved. We have also
what are called monstrosities; but they graduate into varieties. By a mon-
strosity I presume is meant some considerable deviation of structure, gen-
erally injurious, or not useful to the species. Some authors use the term "vari-
ation" in a technical sense, as implying a modification directly due to the
physical conditions of life; and "variations" in this sense are supposed not to
be inherited; but who can say that the dwarfed condition of shells in the
brackish waters of the Baltic, or dwarfed plants on Alpine summits, or the
thicker fur of an animal from far northward, would not in some cases be in-
herited for at least a few generations? And in this case I presume that the
form would be called a variety.

It may be doubted whether sudden and considerable deviations of struc-
ture, such as we occasionally see in our domestic productions, more especially
with plants, are ever permanently propagated in a state of nature. Almost
every part of every organic being is so beautifully related to its complex con-
ditions of life that it seems as improbable that any part should have been sud-
denly produced perfect, as that a complex machine should have been invented
by man in a perfect state. Under domestication monstrosities sometimes occur
which resemble normal structures in widely different animals. Thus pigs have
occasionally been born with a sort of proboscis, and if any wild species of the
same genus had naturally possessed a proboscis, it might have been argued
that this had appeared as a monstrosity; but I have as yet failed to find, after
diligent search, cases of monstrosities resembling normal structures in nearly
allied forms, and these alone bear on the question. If monstrous forms of this

Online LibraryCharles DarwinThe origin of species → online text (page 4 of 50)