The Theory of Sexual Selection. 399 
difficulty of supposing so much similarity and con- 
stancy of taste on the part of female animals as Mr. 
Darwin's theory undoubtedly requires. Although we 
know very little about the psychology of the lower 
animals, we do observe in many cases that small 
details of mental organization are often wonderfully 
constant and uniform throughout all members of a 
species, even where it is impossible to suggest any 
utility as a cause. 
Again, as regards the objection that each bird finds 
a mate under any circumstances, we have here an 
obvious begging of the whole question. That every 
feathered Jack should find a feathered Jill is perhaps 
what we might have antecedently expected ; but when 
we meet with innumerable instances of ornamental 
plumes, melodious songs, and the rest, as so many 
witnesses to a process of sexual selection having 
always been in operation, it becomes irrational to ex- 
clude such evidence on account of our antecedent 
prepossessions. 
There remains the objection that the principles of 
natural selection must necessarily swallow up those of 
sexual selection. And this consideration, I doubt 
not, lies at the root of all Mr. Wallace’s opposition to 
the supplementary theory of sexual selection. He is 
self-consistent in refusing to entertain the evidence of 
sexual selection, on the ground of his antecedent per- 
suasion that in the great drama of evolution there is 
no possible standing-ground for any other actor than 
that which appears in the person of natural selection. 
But here, again, we must refuse to allow any merely 
antecedent presumption to blind our eyes to the 
actual evidence of other agencies having co-operated 
