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 shorter beaks. Again, we
may suppose that at an early period of history, the men of one nation or
district required swifter horses, while those of another required stronger
and bulkier horses. The early differences would be very slight; but, in
the course of time, from the continued selection of swifter horses in the
one case, and of stronger ones in the other, the differences would become
greater, and would be noted as forming two sub-breeds. Ultimately after
the lapse of centuries, these sub-breeds would become converted into two
well-established and distinct breeds.
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