The Descent of Man

fer much in constitution before the power of
reproduction is gained. On the other hand, after
this power has been gained and the sexes
have come to differ in constitution, the gemmules
(if I may again use the language of pangenesis)
which are cast off from each varying part in
the one sex would be much more likely to possess
the proper affinities for uniting with the
tissues of the same sex, and thus becoming developed,
than with those of the opposite sex.
I was first led to infer that a relation of this kind
exists, from the fact that whenever and in whatever
manner the adult male differs from the
adult female, he differs in the same manner
from the young of both sexes. The generality of
this fact is quite remarkable: it holds good with
almost all mammals, birds, amphibians, and
fishes; also with many crustaceans, spiders, and
some few insects, such as certain orthoptera
and libellulae. In all these cases the variations,
through the accumulation of which the male