CHAPTER IX. 



The evidence from secoxdart sexual charac- 

 ters CONTINUED. — THE CAUSE OF THE EXCESSIVE 

 MODIFICATION OF MALE CHARACTERS. 



The Explanation of Daines Barrington and Wallace — Reasons for 

 considering it inadequate — Darwin's explanation — History 

 of domesticated races shows that this does not go to the root 

 of the matter — The view that the male is more exposed than 

 the female to the action of selection — A more fundamental ex- 

 planation is needed — This is furnished by our theory of 

 heredity — Special difficulties — Summary . 



The sexual characteristics of animals have been made 

 the subject of considerable discussion by various nat- 

 uralists, and among birds especially there have been 

 many attempts to explain why the female has not 

 acquired the same ornaments as the male. 



The Explanations of Dai7ies Barringto7i and Wallace. 



Wallace points out that conspicuous ornaments and 

 brilliant plumage would render the female bird promi- 

 nent while incubating, and would thus enable enemies 

 to detect the presence of the nest. He believes that 

 since incubating females are exposed to this danger, natu- 

 ral selection has acted, by the destruction of the most 

 conspicuous females, to gradually produce races in which 

 the females have nothing to render them conspicuous. 



In 1773 the Hon. Daines Barrington called attention 

 {Phil. Trans. 1773, p. 164) to the fact that singing 

 birds are all small, and he believes that this arises from 



