Both hybrids and mongrels can be reduced to either pure parent form, by
repeated crosses in successive generations with either parent.
These several remarks are apparently applicable to animals; but the subject
is here much complicated, partly owing to the existence of secondary sexual
characters; but more especially owing to prepotency in transmitting
likeness running more strongly in one sex than in the other, both when one
species is crossed with another and when one variety is crossed with
another variety. For instance, I think those authors are right who
maintain that the ass has a prepotent power over the horse, so that both
the mule and the hinny resemble more closely the ass than the horse; but
that the prepotency runs more strongly in the male than in the female ass,
so that the mule, which is an offspring of the male ass and mare, is more
like an ass than is the hinny, which is the offspring of the female-ass and
stallion.
Much stress has been laid by some authors on the supposed fact, that it is
only with mongrels that the offspring are not intermediate in character,
but closely resemble one of their parents; but this does sometimes occur
with hybrids, yet I grant much less frequently than with mongrels. Looking
to the cases which I have collected of cross-bred animals closely
resembling one parent, the resemblances seem chiefly confined to characters
almost monstrous in their nature, and which have suddenly appeared--such as
albinism, melanism, deficiency of tail or horns, or additional fingers and
toes; and do not relate to characters which have been slowly acquired
through selection.
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