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Wallace, Alfred Russel, 1823-1913

"Darwinism (1889)"

"
With these numerous facts recorded by competent observers we can hardly
doubt that races of hybrids between these very distinct species have
been produced, and that such hybrids are fairly fertile _inter se_; and
the analogous facts already given lead us to believe that whatever
amount of infertility may at first exist could be eliminated by careful
selection, if the crossed races were bred in large numbers and over a
considerable area of country. This case is especially valuable, as
showing how careful we should be in assuming the infertility of hybrids
when experiments have been made with the progeny of a single pair, and
have been continued only for one or two generations.
Among insects one case only appears to have been recorded. The hybrids
of two moths (Bombyx cynthia and B. arrindia) were proved in Paris,
according to M. Quatrefages, to be fertile _inter se_ for eight
generations.

_Fertility of Hybrids among Plants._
Among plants the cases of fertile hybrids are more numerous, owing, in
part, to the large scale on which they are grown by gardeners and
nurserymen, and to the greater facility with which experiments can be
made.


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