The Variation of Animals and Plants under Domestication, vol 1 | Page 8

cultivated races of plants often exhibit an
abnormal character, as compared with natural species; for they have
been modified not for their own benefit, but for that of man.
In another work I shall discuss, if time and health permit, the variability
of organic beings in a state of nature; namely, the individual differences
presented by animals and plants, and those slightly greater and
generally inherited differences which are ranked by naturalists as
varieties or geographical races. We shall see how difficult, or rather
how impossible it often is, to distinguish between races and sub-species,
as the less well- marked forms have sometimes been denominated; and
again between sub-species and true species. I shall further attempt to
show that it is the common and widely ranging, or, as they may be
called, the dominant species, which most frequently vary; and that it is
the large and flourishing genera which include the greatest number of
varying species. Varieties, as we shall see, may justly be called
incipient species.
But it may be urged, granting that organic beings in a state of nature
present some varieties,--that their organisation is in some slight degree
plastic; granting that many animals and plants have varied greatly
under domestication, and that man by his power of selection has gone
on accumulating such variations until he has made strongly marked and
firmly inherited races; granting all this, how, it may be asked, have
species arisen in a state of nature? The differences between natural
varieties are slight; whereas the differences are considerable between
the species of the same genus, and great between the species of distinct
genera. How do these lesser differences become augmented into the
greater difference? How do varieties, or as I have called them incipient
species, become converted into true and well-defined species? How has
each new species been adapted to the surrounding physical conditions,
and to the other forms of life on which it in any way depends? We see
on every side of us innumerable adaptations and contrivances, which
have justly excited the highest admiration of every observer. There is,
for instance, a fly (Cecidomyia (Introduction/3. Leon Dufour in
'Annales des Science. Nat.' (3rd series, Zoolog.) tome 5 page 6.)) which
deposits its eggs within the stamens of a Scrophularia, and secretes a
poison which produces a gall, on which the larva feeds; but there is

another insect (Misocampus) which deposits its eggs within the body of
the larva within the gall, and is thus nourished by its living prey; so that
here a hymenopterous insect depends on a dipterous insect, and this
depends on its power of producing a monstrous growth in a particular
organ of a particular plant. So it is, in a more or less plainly marked
manner, in thousands and tens of thousands of cases, with the lowest as
well as with the highest productions of nature.
This problem of the conversion of varieties into species,--that is, the
augmentation of the slight differences characteristic of varieties into the
greater differences characteristic of species and genera, including the
admirable adaptations of each being to its complex organic and
inorganic conditions of life,--has been briefly treated in my 'Origin of
Species.' It was there shown that all organic beings, without exception,
tend to increase at so high a ratio, that no district, no station, not even
the whole surface of the land or the whole ocean, would hold the
progeny of a single pair after a certain number of generations. The
inevitable result is an ever-recurrent Struggle for Existence. It has truly
been said that all nature is at war; the strongest ultimately prevail, the
weakest fail; and we well know that myriads of forms have disappeared
from the face of the earth. If then organic beings in a state of nature
vary even in a slight degree, owing to changes in the surrounding
conditions, of which we have abundant geological evidence, or from
any other cause; if, in the long course of ages, inheritable variations
ever arise in any way advantageous to any being under its excessively
complex and changing relations of life; and it would be a strange fact if
beneficial variations did never arise, seeing how many have arisen
which man has taken advantage of for his own profit or pleasure; if
then these contingencies ever occur, and I do not see how the
probability of their occurrence can be doubted, then the severe and
often-recurrent struggle for existence will determine that those
variations, however slight, which are favourable shall be preserved or
selected, and those which are unfavourable shall be destroyed.
This preservation, during the battle for life, of varieties which possess
any advantage in structure, constitution, or instinct, I have called
Natural Selection; and Mr. Herbert Spencer has well expressed the
same idea by the Survival