The Descent of Man

to vary, both with animals in a state of nature
and under domestication. (43. On these points
see also 'Variation of Animals and Plants under
Domestication,' vol. i. p. 253; vol ii. pp. 73, 75.)
There is also reason to believe, as we have seen
in our eighth chapter, that variations are more
apt to occur in the male than in the female sex.
All these contingencies are highly favourable
for sexual selection. Whether characters thus
acquired are transmitted to one sex or to both
sexes, depends, as we shall see in the following
chapter, on the form of inheritance which prevails.
It is sometimes difficult to form an opinion
whether certain slight differences between the
sexes of birds are simply the result of variability
with sexually-limited inheritance, without
the aid of sexual selection, or whether they
have been augmented through this latter process.
I do not here refer to the many instances
where the male displays splendid colours or