most, and by destroying the worthless individuals, slowly, though surely,
induces great changes. As the will of man thus comes into play, we can
understand how it is that domesticated breeds show adaptation to his wants
and pleasures. We can further understand how it is that domestic races of
animals and 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