nd finally extinct. The forms which
stand in closest competition with those undergoing modification and
improvement, will naturally suffer most. And we have seen in the
chapter on the Struggle for Existence that it is the most closely-allied
forms,--varieties of the same species, and species of the same genus
or of related genera,--which, from having nearly the same structure,
constitution, and habits, generally come into the severest competition
with each other. 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 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