Along with these larger variations others of smaller amount
occasionally appear, sometimes in external, sometimes in internal
characters, the very bones of the skeleton often changing slightly in
form, size, or number; but as these secondary characters have been of no
use to man, and have not been specially selected by him, they have,
usually, not been developed to any great amount except when they have
been closely dependent on those external characters which he has largely
modified.
As man has considered only utility to himself, or the satisfaction of
his love of beauty, of novelty, or merely of something strange or
amusing, the variations he has thus produced have something of the
character of monstrosities. Not only are they often of no use to the
animals or plants themselves, but they are not unfrequently injurious to
them. In the Tumbler pigeons, for instance, the habit of tumbling is
sometimes so excessive as to injure or kill the bird; and many of our
highly-bred animals have such delicate constitutions that they are very
liable to disease, while their extreme peculiarities of form or
structure would often render them quite unfit to live in a wild state.
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