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. Asa 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 
