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 
relationship of thesexes. 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 
