[53] In India, according to
Mr. Blyth and Captain Hutton, whole flocks of these hybrid geese are
kept in various parts of the country where neither of the pure parent
species exists, and as they are kept for profit they must certainly be
fully fertile.
Another equally striking case is that of the Indian humped and the
common cattle, species which differ osteologically, and also in habits,
form, voice, and constitution, so that they are by no means closely
allied; yet Mr. Darwin assures us that he has received decisive
evidence that the hybrids between these are perfectly fertile _inter
se_.
Dogs have been frequently crossed with wolves and with jackals, and
their hybrid offspring have been found to be fertile _inter se_ to the
third or fourth generation, and then usually to show some signs of
sterility or of deterioration. The wolf and dog may be originally the
same species, but the jackal is certainly distinct; and the appearance
of infertility or of weakness is probably due to the fact that, in
almost all these experiments, the offspring of a single pair--themselves
usually from the same litter--- were bred in-and-in, and this alone
sometimes produces the most deleterious effects.
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