But on the view that groups of
species have descended from other species, and have been modified
through natural selection, I think we can obtain some light. In our
domestic animals, if any part, or the whole animal, be neglected and
no selection be applied, that part (for instance, the comb in the
Dorking fowl) or the whole breed will cease to have a nearly uniform
character. The breed will then be said to have degenerated. In
rudimentary organs, and in those which have been but little
specialised for any particular purpose, and perhaps in polymorphic
groups, we see a nearly parallel natural case; for in such cases
natural selection either has not or cannot come into full play, and
thus the organisation is left in a fluctuating condition. But what
here more especially concerns us is, that in our domestic animals
those points, which at the present time are undergoing rapid change by
continued selection, are also eminently liable to variation. Look at
the breeds of the pigeon; see what a prodigious amount of difference
there is in the beak of the different tumblers, in the beak and wattle
of the different carriers, in the carriage and tail of our fantails,
etc., these being the points now mainly attended to by English
fanciers. Even in the sub-breeds, as in the short-faced tumbler, it is
notoriously difficult to breed them nearly to perfection, and
frequently individuals are born which depart widely from the standard.
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