animals one variety certainly often has this prepotent power over
another variety. Hybrid plants produced from a reciprocal cross,
generally resemble each other closely; and so it is with mongrels from
a reciprocal cross. 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 excessively 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 more resemble the ass
than the horse; but that the prepotency runs more strongly in the
male-ass than in
the female, so that the mule, which is the 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
mongrel animals alone are born closely like one of their parents; but
it can be shown that this does sometimes occur with hybrids; yet I
grant much less frequently with hybrids 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 by selection. Consequently, sudden reversions to
the perfect character of either parent would be more likely to occur
with mongrels, which are descended from varieties often suddenly
produced and semi-monstrous in character, than with hybrids, which are
descended from species slowly and naturally produced. On the whole I
entirely agree with Dr. Prosper Lucas, who, after arranging an enormous
body of facts with respect to animals, comes to the conclusion, that
the laws of resemblance of the child to its parents are the same,
whether the two parents differ much or little from each other, namely
in the union of individuals of the same variety, or of different
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