198 Animal Life and Intelligence. 



backs, the metallic hues of male butterflies, and the large 

 horns or antennae of other insects, these and many other 

 examples which will at once occur to the reader are 

 illustrations of the fact. 



As a contribution towards the explanation of this order 

 of phenomena, Darwin brought forward his hypothesis of 

 sexual selection, of which there are two modes. In the 

 first place, the males struggle together for their mates ; in 

 this struggle the weakest are eliminated ; those possessed 

 of the most efficient weapons of offence and defence escape 

 elimination. In the second place, the females are repre- 

 sented as exercising individual choice, and selecting (in 

 the true sense of the word) those mates whose bright 

 colours, clear voices, or general strength and vigour render 

 them most pleasing and attractive. For this mode I shall 

 employ the term "preferential mating." Combining these 

 two in his summary, Darwin says, " It has been shown 

 that the largest number of vigorous offspring will be reared 

 from the pairing of the strongest and best-formed males, 

 victorious in contests over other males, with the most 

 vigorous and best-nourished females, which are the first 

 to breed in the spring. If such females select the more 

 attractive and, at the same time, vigorous males, they will 

 rear a larger number of offspring than the retarded females, 

 which must pair with the less vigorous and less attractive 

 males. So it will be if the more vigorous males select 

 the more attractive and, at the same time, healthy and 

 vigorous females ; and this will especially hold good if the 

 male defends the female, and aids in providing food for 

 the young. The advantage thus gained by the more 

 vigorous pairs in rearing a larger number of offspring has 

 apparently sufficed to render sexual selection efficient."* 



With regard to the first of the two modes, little need 

 be said. There can be no question that there are both 

 elimination by battle and elimination by competition in 

 the struggle for mates. It is well known that the emperor 

 moth discovers his mate by his keen sense of smell residing 



* Darwin, " Descent of Man," pt. ii. cliap. viii. 



