Rau — Sexual Selection Experiments in Cecropia Moth. 307 



tion which decides the choice of the insects. We do not 

 know what senses or attractions may exist which we have 

 not perceived. 



The experiments bring to light the strength of one 

 factor which has not yet received the consideration due 

 its importance, viz., age. We have matched youth against 

 middle and old age in both sexes, and many times under 

 handicap too, and yet in the majority of cases we see the 

 younger individual, even though seriously defective, win- 

 ning over the older rival. To just how fine a point this 

 advantage will hold, we cannot safely say, while other 

 factors which determine choice are undiscovered, but in 

 our experiments we find the younger individual still the 

 winner when the difference in ages is only fifteen or even 

 ten minutes. 



Theories have been based upon the hypothesis of choice 

 of the beautiful and well qualified on one side and victory 

 by strength on the other. The experiments show in most 

 cases where behavior was noted (and the same was true 

 in a general way in the experiments which could not be 

 recorded in detail) that the female exercised no choice. 

 In the few cases where her choice was evident, it was sur- 

 prisingly varied ; she showed her preference for the plain 

 or even pitifully defective or mutilated mate as readily 

 as for a fine, perfect one. 



The males, perhaps, show a little more choice in the 

 matter, yet here too youth is the element which decides 

 more ^* matches^' than any other, so far as we can see. 



But we must not lose sight of the fact that, while selec- 

 tion clearly works toward youth, this does not necessarily 

 mean working toward the more fit in individual varia- 

 tions, because it is only a matter of chance whether the 

 beautiful one is the younger when the competition occurs. 

 But here we are again left in doubt about the extent to 

 which the male selects by victory of strength when we see 

 the young, wingless males winning almost every time 

 over the normal ones. 



