ng 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, etc., 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.

2. 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