Darwin's Theory of Sexual Selection 221 



ences amongst animals. Other attempts to explain these 

 differences have been equally unsuccessful. Thus Wallace 

 accounts for them as due to the excessive vigor of the male, 

 but Darwin's reply to Wallace appears to show that this is 

 not the cause of the* difference. He points out that, while 

 the hypothesis might appear plausible in the case of color, 

 it is not so evident in the case of other secondary sexual 

 characters, such, for instance, as the musical apparatus of the 

 males of certain insects, and the difference in the size of the 

 larynx of certain birds and mammals. 



Darwin's theory served to draw attention to a large num- 

 ber of most interesting differences between the sexes, and, 

 even if it prove to be a fiction, it has done much good in 

 bringing before us an array of important facts in regard to 

 differences in secondary sexual characters. More than this I 

 do not believe it has done. The theory meets with fatal ob- 

 jections at every turn. 



In a later chapter the question will be more fully discussed 

 as to the sense in which these secondary sexual differences 

 may be looked upon as adaptations. 



