Wallace's Theory 



such weapons on account of their being useless, 

 superfluous, or in some way injurious. On the 

 contrary, as they are often used by the males for 

 various purposes, more especially as a defence 

 against their enemies, it is a surprising fact that 

 they are so poorly developed, or quite absent, 

 in the females of so many animals." 



We have, we believe, demonstrated that 

 Darwin's theory of sexual selection is unable to 

 account satisfactorily for all the phenomena of 

 sexual dimorphism. But, as we have seen, it is 

 quite possible that sexual selection is a real 

 factor of evolution. 



We trust that what we have said will stimu- 

 late some leisured naturalist to study the question 

 of male and female preference. 



We now pass on to consider briefly some of 

 the other attempts that have been made to ex- 

 plain the phenomena of sexual dimorphism. 



WALLACE'S EXPLANATION OF SEXUAL 

 DISSIMILARITY 



Wallace does not accept the theory of sexual 

 selection. He admits that the form of male 

 rivalry, which Darwin calls " the law of battle," 

 is "a real power in nature," and believes that 

 " to it we must impute the development of the 

 exceptional strength, size, and activity of the 

 male, together with the possession of special 

 offensive and defensive weapons, and of all 

 x 321 



