58 ORGANIC EVOLUTION 



greater effectiveness in the act of pairing, and that this 

 difference in mental character in the two sexes has been 

 brought about by natural selection because of its usefulness, 

 and has not been developed through the females choosing 

 the more ardent males. (Compare page 54.) 



Sometimes it is the female and not the male which 

 shows the greater development of secondary sexual charac- 

 ters (Fig. 8, B and C). In these forms we have no evidence 

 of the exercise of choice by the male or of ardent courtship 

 by the female. These cases, however, are rare, and we do 

 not know what may be the use of the special appendages. 



Wallace urges that for sexual selection to produce the 

 results claimed the less ornamented males must fail to find 

 mates, and, he says, we have no evidence that the less 

 adorned males do fail to obtain mates, but that, on the con- 

 trary, the less adorned as well as the highly ornamented 

 have offspring. 



This statement of Wallace's is not surely true. If there 

 is a correlation between vigor and high development of the 

 ornamental sexual characters, as there is between vigor and 

 high development of other structures, then, though the less 

 ornamented males may obtain mates, they are less vigorous 

 and will have less vigorous offspring. If it be also true that 

 the more vigorous females are more sought after by the 

 males than are their less vigorous sisters, then they w r ill have 

 first choice of the males, choosing the most highly orna- 

 mented, which are at the same time the more vigorous. 



o 



Thus the vigorous, highly ornamented males will mate with 

 the vigorous females, having vigorous offspring, while the 

 less ornamented and less vigorous males will mate with the 

 less vigorous females and have less vigorous offspring. Nat- 



