Consequently, each new variety or species, during the progress
of its formation, will generally press hardest on its nearest kindred, and
tend to exterminate them. We see the same process of extermination amongst
our domesticated productions, through the selection of improved forms by
man. Many curious {111} instances could be given showing how quickly new
breeds of cattle, sheep, and other animals, and varieties of flowers, take
the place of older and inferior kinds. In Yorkshire, it is historically
known that the ancient black cattle were displaced by the long-horns, and
that these "were swept away by the short-horns" (I quote the words of an
agricultural writer) "as if by some murderous pestilence."

_Divergence of Character._--The principle, which I have designated by this
term, is of high importance on my theory, and explains, as I believe,
several important facts. In the first place, varieties, even
strongly-marked ones, though having somewhat of the character of
species--as is shown by the hopeless doubts in many cases how to rank
them--yet certainly differ from each other far less than do good and
distinct species. Nevertheless, according to my view, varieties are species
in the process of formation, or are, as I have called them, incipient
species. How, then, does the lesser difference between varieties become
augmented into the greater difference between species? That this does
habitually happen, we must infer from most of the innumerable species
throughout nature presenting well-marked differences; whereas varieties,
the supposed prototypes and parents of future well-marked species, present
slight and ill-defined differences. Mere chance, as we may call it, might
cause one variety to differ in some character from its parents, and the
offspring of this variety again to differ from its parent in the very same
character and in a greater degree; but this alone would never account for
so habitual and large an amount of difference as that between varieties of
the same species and species of the same genus.

As has always been my practice, let us seek light on {112} this head from
our domestic productions. We shall here find something analogous. A fancier
is struck by a pigeon having a slightly shorter beak; another fancier is
struck by a pigeon having a rather longer beak; and on the acknowledged
principle that "fanciers do not and will not admire a medium standard, but
like extremes," they both go on (as has a