446 Experimental Zoology 



the physiological conditions under which they were originally 

 produced," etc. Thus the secondary sexual characters ac- 

 quired by the adult male became inherited .only by the males 

 and at the same time of life at which they first appeared in the 

 male. As a purely formal assumption no objection can be made 

 to this kind of hypotheses. Our opinion as to whether it is 

 probable or not must be guided by the experimental evidence 

 that can be brought forward in its support. At present this evi- 

 dence is lacking. 



It seems to me that Wallace's view, that the secondary sexual 

 differences may be due to the greater "vitality" of the male 

 (which has resulted from the natural selection of the stronger 

 males), may be given a much simpler interpretation without neces- 

 sitating the assumption of any process of selection. When we 

 see the wonderful development in all groups of the animal king- 

 dom of pigmentation, and when we realize that there are inherent 

 differences between the males and females of each species, it is 

 not surprising that differences in color might also appear asso- 

 ciated with the male and female condition. So long as these 

 differences do not seriously interfere with the existence of the 

 species, they will perpetuate themselves. Only if carried too 

 far might the species exterminate itself. There is no need of 

 selection to account for their origin. At most " selection " might 

 account for their destruction if they develop beyond a certain 

 point. 



This mode of explanation will not, I am aware, appeal to 

 those naturalists of the Darwinian school who attempt to explain 

 all organic conditions as the result of usefulness. They seek 

 to find a purpose in every existing condition, and therefore try to 

 find some purpose for the secondary sexual differences between 

 the male and the female. That a great number of the charac- 

 teristics of organisms have a purpose there can be little question. 

 This purpose is the maintenance of the species ; but it is not logi- 

 cal to assume that because a great number of adaptations exist, 

 all characters must therefore be adaptations to something or 

 other, at least in the sense that they have a survival value. The 



