explains, as I believe, the well-known fact, that in a number of cases we
cannot recognise, and therefore do not know, the wild parent-stocks of the
plants which have been longest cultivated in our flower and kitchen
gardens. If it has taken centuries or thousands of years to improve or
modify most of our plants up to their present standard of usefulness to
man, we can understand how it is that neither Australia, the Cape of Good
Hope, nor any other region inhabited by quite uncivilised man, has afforded
us a single plant worth culture. It is not that these countries, so rich
in species, do not by a strange chance possess the aboriginal stocks of any
useful plants, but that the native plants have not been improved by
continued selection up to a standard of perfection comparable with that
acquired by the plants in countries anciently civilised.

In regard to the domestic animals kept by uncivilised man, it should not be
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 why the varieties kept by savages, as has been
remarked by some authors, have more of the character of true species than
the varieties kept in civilised countries.

On the view here given of the 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.