Origin of Different Kinds of Adaptations 373 
organs in one sex appear in the light of adaptations to certain 
instincts in the other sex. It would, perhaps, appear to 
simplify the problem to deny outright that any such relation 
exists ; but I think, in the light of the evidence that we have, 
this procedure would be like that of the proverbial ostrich, 
which is supposed to stick its head in the sand in order to 
escape an anticipated danger. If we assumed this agnostic 
position, we might attempt to account for the appearance of 
secondary sexual organs as mutations that had appeared in 
one sex, and had no immediate connection with the other 
sex; and, so long as these organs were not directly and 
seriously injurious, we might assume that the animals in 
which such structures had appeared might be able to exist. 
But, on the other hand, I think that an examination of the 
evidence will show that this way out of the difficulty is not- 
very satisfactory, for the organs in question appear, in some 
cases at least, to be closely connected with certain definite 
responses in the other sex. Moreover, as Darwin has so 
insistently pointed out, the action of the males is of such a 
sort that it is evidently associated with the presence of the 
secondary sexual organs which they often display before the 
other sex. Furthermore, the greater and often exclusive 
development of these organs during the sexual period dis- 
tinctly points to them as in some way connected with the 
relation of the sexes to each other. And finally, there is a 
small, although not entirely convincing, body of evidence, 
indicating that the female is influenced by the action of 
the male; but I do not think that this evidence shows 
that she selects one individual at the expense of all 
other rivals. We meet here with a problem that is as pro- 
foundly interesting as it is obscure. In fact, if we admit 
that this relation exists we have a double set of conditions to 
deal with: first, the development in the males of certain 
secondary sexual organs; and secondly, the instinct to dis- 
play these organs. The supposed influence of the display on 
