ing in each successive generation the individuals which he prizes
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 a second work I shall discuss 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 organization 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 {5} considerable between the species of
the same genus, and great between the species of distinct genera. How do
these lesser differences become augmented into the greater difference? How
do varieties, or as I have called them incipient species, become converted
into true and well-defined species? How has each new species been adapted
to the surrounding physical conditions, and to the other forms of life on
which it in any way depends? We see on every side of us innumerable
adaptations and contrivances, which have justly excited in the mi