s,
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, 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 far less from each
other 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 a degree of difference as that between the species of the same
genus.

As has always been my practice, I have sought light on this head from
our domestic productions. We shall here find something analogous. It
will be admitted that the production of races so different as short-horn
and Hereford cattle, race and cart horses, the several breeds of
pigeons, etc., could never have been effected by the mere chance
accumulation of similar variations during many successive generations.
In practice, a fancier is, for instance, 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 actually occurred with the sub-breeds of the
tumbler-pigeon) choosing and breeding from birds with longer and longer
beaks, or with shorter and sho