‘Chap. XVIII. 
SUMMARY. 
313 
called sexual selection. This does not depend on any 
superiority in the general struggle for life, but on 
certain individuals of one sex, generally the male sex, 
having been successful in conquering other males, and 
on their having left a larger number of offspring to 
inherit their superiority, than the less successful males. 
There is another and more peaceful kind of contest, 
in which the males endeavour to excite or allure the 
females by various charms. This may be effected by 
the powerful odours emitted by the males during the 
breeding-season; the odoriferous glands having been 
acquired through sexual selection. Whether the same 
view can be extended to the voice is doubtful, for the 
vocal organs of the males may have been strengthened 
by use during maturity, under the powerful excitements 
of love, jealousy, or rage, and transmitted to the same 
sex. Various crests*, tufts, and mantles of hair, which 
are either confined to the male, or are more developed 
in this sex than in the females, seem in most cases to 
be merely ornamental, though they sometimes serve as 
a defence against rival males. There is even reason to 
suspect that the branching horns of stags, and the 
elegant horns of certain antelopes, though properly 
serving as weapons of offence or of defence, have been 
partly modified for the sake of ornament. 
When the male differs in colour from the female he 
generally exhibits darker and more strongly-contrasted 
tints. We do not in this class meet with the splendid 
red, blue, yellow, and green colours, so common with 
male birds and many other animals. The naked parts, 
however, of certain Quadrumana must be excepted ; for 
such parts, often oddly situated, are coloured in some^ 
species in the most brilliant manner. The colours of 
ihe male in other cases may be due to simple variation. 
