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 w
hich 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.
Chapter II
Variation Under Nature
Variability -- Individual differences -- Doubtful species -- Wide ranging,
much diffused, and common species vary most -- Species of the larger genera
in any country vary more than the species of the smaller genera -- Many of
the species of the larger genera resemble varieties in being very closely,
but unequally, 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 at all properly, a
long catalogue of dry facts should be given; but these I shall reserve for
my future work. Nor shall I here discuss the various definitions which
have been given of the term species. No one definition has as yet
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 monstrosity I
presume is meant some considerable deviation of structure in one part,
either injurious to or not useful to the species, and not generally
propagated. Some authors use the term 'variation' 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 northwards, would not in some cases be inherited for at
least some few generations? and in this case I presume that the form would
be called a variety.
Again, we have many slight differences which may be called individual
differences, such as are known frequently to appear in the offspring from
the same parents, or which may be presumed to have thus arisen, from being
frequently observed in the individuals of the same species inhabiting the
same confined locality. No one supposes that all the individuals of the
same species are cast in the very same mould. These individual differences
are highly important for us, as they afford materials for natural selection
to accumulate, in the same manner as man can accumulate in any given
direction individual differences in his domesticated productions. These
individual differences generally affect what naturalists consider
unimportant parts; but I could show by a long catalogue of facts, that
parts which must be called important, whether viewed under a physiological
or classificatory point of view, sometimes vary in the individuals of the
same species. I am convinced that the most experienced naturalist would be
surprised at the number of the cases of variability, even in important
parts of structure, which he could collect on good authority, as I have
collected, during a course of years. It should be remembered that
systematists are far from pleased at finding variability in important
characters, and that there are not many men who will laboriously examine
internal and important organs, and compare them in many specimens of the
same specie
s. I should never have expected that the branching of the main
nerves close to the great central ganglion of an insect would have been
variable in the same species; I should have expected that changes of this
nature could have been effected only by slow degrees: yet quite recently
Mr. Lubbock has shown a degree of variability in these main nerves in
Coccus, which may almost be compared to the irregular branching of the stem
of a tree. This philosophical naturalist, I may add, has also quite
recently shown that the muscles in the larvae of certain insects are very
far from uniform. Authors sometimes argue in a circle when they state that
important organs never vary; for these same authors practically rank that
character as important (as some few naturalists have honestly confessed)
which does not vary; and, under this point of view, no instance of any
important part varying will ever be found: but under any other point of
view many instances assuredly can be given.
There is one point connected with individual differences, which seems to me
extremely perplexing: I refer to those genera which have sometimes been
called 'protean' or 'polymorphic,' in which the species present an
inordinate amount of variation; and hardly two naturalists can agree which
forms to rank as species and which as varieties. We may instance Rubus,
Rosa, and Hieracium amongst plants, several genera of insects, and several
genera of Brachiopod shells. In most polymorphic genera some of the
species have fixed and definite characters. Genera which are polymorphic
in one country seem to be, with some few exceptions, polymorphic in other
countries, and likewise, judging from Brachiopod shells, at former periods
of time. These facts seem to be very perplexing, for they seem to show
that this kind of variability is independent of the conditions of life. I
am inclined to suspect that we see in these polymorphic genera variations
in points of structure which are of no service or disservice to the
species, and which consequently have not been seized on and rendered
definite by natural selection, as hereafter will be explained.
Those forms which possess in some considerable degree the character of
species, but which are so closely similar to some other forms, or are so
closely linked to them by intermediate gradations, that naturalists do not
like to rank them as distinct species, are in several respects the most
important for us. We have every reason to believe that many of these
doubtful and closely-allied forms have permanently retained their
characters in their own country for a long time; for as long, as far as we
know, as have good and true species. Practically, when a naturalist can
unite two forms together by others having intermediate characters, he
treats the one as a variety of the other, ranking the most common, but
sometimes the one first described, as the species, and the other as the
variety. But cases of great difficulty, which I will not here enumerate,
sometimes occur in deciding whether or not to rank one form as a variety of
another, even when they are closely connected by intermediate links; nor
will the commonly-assumed hybrid nature of the intermediate links always
remove the difficulty. In very many cases, however, one form is ranked as
a variety of another, not because the intermediate links have actually been
found, but because analogy leads the observer to suppose either that they
do now somewhere exist, or may formerly have existed; and here a wide door
for the entry of doubt and conjecture is opened.
Hence, in determining whether a form should be ranked as a species or a
variety, the opinion of naturalists having sound judgment and wide
experience seems the only guide to follow. We must, however, in many
cases, decide by a majority of naturalists, for few well-marked and
well-known varieties can be named which have not been ranked as species by