readiness with which such varieties originate that a certain amount of
disturbance would carry them beyond the influence of the primordial
attraction, where they may become new centres of variation.

Some suppose that races cannot be perpetuated indefinitely even by keeping
up the conditions under which they were fixed; but the high antiquity of
several, and the actual fixity of many of them, negative this assumption.
"To assert that we could not breed our cart and race horses, long and short
horned cattle, and poultry of various breeds, for almost an infinite number
of generations, would be opposed to all experience."

Why varieties develop so readily and deviate so widely under domestication,
while they are apparently so rare or so transient in free Nature, may
easily be shown. In Nature, even with hermaphrodite plants, there is a vast
amount of cross-fertilization among various individuals of the same
species. The inevitable result of this (as was long ago explained in this
Journal [I-7]) is to repress variation, to keep the mass of a species
comparatively homogeneous over any area in which it abounds in individuals.
Starting from a suggestion of the late Mr. Knight, now so familiar, that
close interbreeding diminishes vigor and fertility; [I-8] and perceiving
that bisexuality is ever aimed at in Nature--being attained physiologically
in numerous cases where it is not structurally--Mr. Darwin has worked out
the subject in detail, and shown how general is the concurrence, either
habitual or occasional, of two hermaphrodite individuals in the
reproduction of their kind; and has drawn the philosophical inference that
probably no organic being self-fertilizes indefinitely; but that a cross
with another individual is occasionally--perhaps at very long
intervals--indispensable. We refer the reader to the section on the
intercrossing of individuals (pp. 96--101), and also to an article in the
Gardeners' Chronicle a year and a half ago, for the details of a very