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 same species and species of the same genus.
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