in favour of this view: to assert that we could not breed our cart and
race-horses, long and short-horned cattle, and poultry of various
breeds, and esculent vegetables, for an almost infinite number of
generations, would be opposed to all experience. I may add, that when
under nature the conditions of life do change, variations and
reversions of character probably do occur; but natural selection, as
will hereafter be explained, will determine how far the new characters
thus arising shall be preserved.

When we look to the hereditary varieties or races of our domestic
animals and plants, and compare them with species closely allied
together, we generally perceive in each domestic race, as already
remarked, less uniformity of character than in true species. Domestic
races of the same species, also, often have a somewhat monstrous
character; by which I mean, that, although differing from each other,
and from the other species of the same genus, in several trifling
respects, they often differ in an extreme degree in some one part,
both when compared one with another, and more especially when compared
with all the species in nature to which they are nearest allied. With
these exceptions (and with that of the perfect fertility of varieties
when crossed,--a subject hereafter to be discussed), domestic races of
the same species differ from each other in the same manner as, only in
most cases in a lesser degree than, do closely-allied species of the
same genus in a state of nature. I think this must be admitted, when
we find that there are hardly any domestic races, either amongst
animals or plants, which have not been ranked by some competent judges
as mere varieties, and by other competent judges as the descendants of
aboriginally distinct species. If any marked distinction existed
between domestic races and species, this source of doubt could not so
perpetually recur. It has often been stated that domestic races do not