The Theory of Sexual Selection. 395 



tiful a design of colours. Moreover, this design is only 

 unfolded when the tail is erected, and the tail is not 

 erected in battle (as Mr. Wallace's theory of the 

 erectile function in feathers would require), but in 

 courtship ; obviously, therefore, the purpose of the 

 pattern, so to speak, is correlated with the act of 

 courtship it being only then, in fact, that the general 

 purpose of the whole structure, as well as the more 

 special purpose of the pattern, becomes revealed. 

 Lastly, the fact of this whole structure being so large, 

 entailing not only a great amount of physiological 

 material in its production, but also of physiological 

 energy in carrying about such a weight, as well as of 

 increased danger from impeding locomotion and in- 

 viting capture all this is obviously incompatible with 

 the supposition of the peacock's tail having been pro- 

 duced by natural selection. And such a case does 

 not stand alone. There are multitudes of other in- 

 stances of ornamental structures imposing a drain 

 upon the vital energies of their possessors, without 

 conferring any compensating benefit from a utilitarian 

 point of view. Now, in all these cases, without any 

 exception, such structures are ornamental structures 

 which present a plain and obvious reference to the 

 relationsh ip of the sexes. Therefore it becomes almost 

 impossible to doubt first, that they exist for the sake 

 of ornament ; and next, that the ornament exists on 

 account of that relationship. If such structures were 

 due merely to a superabundance of energy, as Mr. 

 Wallace supposes, not only ought they to have been 

 kept down by the economizing influence of natural 

 selection ; but we can see no reason, either why they 

 should be so highly ornamental on the one hand, or 



