The Descent of Man

continued intercrossing. Such variations come
under the provisional class, alluded to in our
second chapter, which for want of a better term
are often called spontaneous. Nor do I pretend
that the effects of sexual selection can be indicated
with scientific precision; but it can be
shewn that it would be an inexplicable fact if
man had not been modified by this agency,
which appears to have acted powerfully on
innumerable animals. It can further be shewn
that the differences between the races of man,
as in colour, hairiness, form of features, etc., are
of a kind which might have been expected to
come under the influence of sexual selection.
But in order to treat this subject properly, I
have found it necessary to pass the whole animal
kingdom in review. I have therefore devoted
to it the Second Part of this work. At the
close I shall return to man, and, after attempting
to shew how far he has been modified
through sexual selection, will give a brief
summary of the chapters in this First Part.