Darwin s Theory of Sexual Selection 2 1 9 



This is explained as possibly merely the result of "continued 

 growth." The improbability of selection is manifest in these 

 cases, but if "continued growth " can accomplish this much, 

 why may not the whole process be also the outcome of such 

 growth ? At any rate, whatever the explanation is, it is im- 

 portant to find a case of a secondary sexual character that the 

 hypothesis obviously is insufficient to explain. 



15. It is admitted in a number of cases, as in the stag for 

 instance, that, although the larynx of the male is enlarged, 

 this is not, in all probability, the outcome of sexual selection, 

 but in other forms this same enlargement is ascribed to the 

 selection process. 



16. It is admitted that in none of the highly colored 

 British moths is there much difference according to sex, 

 although when a difference of color is found in butterflies 

 this is put down to the action of sexual selection. If such 

 wonderful colors as those of moths can arise without the 

 action of selection, why make a special explanation for those 

 cases in which this difference is associated with sex ? 



17. It is well known that birds sing at other times of the 

 year than at the breeding season, and an attempt is made to 

 account for this in that birds take pleasure in practising those 

 instincts that they make use of at other times, as the cat 

 plays with the captive mouse. Does not this suggest that, 

 if they had certain instincts, they would- be more likely to 

 employ them at the times when their vitality or excitement 

 is at its highest without regard to the way in which they have 

 come by them ? 



18. The color of the iris of the eyes of many species of 

 hornbills is said to be an intense crimson in the males, and 

 white in the females. In the male condor the eye is yellowish 

 brown, and in the female a bright red. Darwin admits that 

 it is doubtful if this difference is the result of sexual selec- 

 tion, since in the latter case the lining of the mouth is black 

 in the males, and flesh-colored in the females, which does not 



