THE SEXES AND SEXUAL SELECTION. 15 



SUMMARY. 



I, 2. The existence of male and female animals is a commonplace of 

 observation. They differ in primary and in secondary sexual characters, 

 of which illustrations are given, chiefly from Darwin. 



3. Darwin's hypothesis of sexual selection assumes the preservation and 

 perfection of variations, advantageous in courtship or in battles with rivals. 



4. Wallace maintains that the females have been protectively retarded 

 by natural selection ; Brooks, that the males predominate in power of 

 transmitting variations, and are therefore more divergent; while Mivart 

 demands a deeper analysis than is afforded by either sexual or natural selec- 

 tion, — such a physiological rationale being hinted at. 



LITERATURE. 



Brooks (W. K.)— The Law of Heredity : A Study of the Cause of Varia- 

 tion and the Origin of Living Organisms. Baltimore, 1883. 



Darwin (C.) — On the Origin of Species by Means of Natural Selection; 

 or, The Preservation of Favoured Races in the Struggle for Life. 

 London, 1859. 



The Descent of Man, and Selection in Relation to Sex. London, 



1871. 



MiVART (St George) — Lessons from Nature. London, 1876. 



Wallace (A. R.) — Contributions to the Theory of Natural Selection. 

 London, 1871. 



• Darwinism : An Exposition of the Theory of Natural Selection, 



with Some of its Applications, London, 1889. 



