Chap. XVIII. SUMMARY. 31.'^ 



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 conquerinn^ 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 merelv ornamental, thouo:h thev 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, thougli properly 

 serving as weapons of offence or of defence, have been 

 partly modified for the sake of ornament. 



AVhen 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 

 the male in other cases may be due to simple variation, 



