THE SEXUAL SELECTION THEORY 141 



the first place, the duller-witted birds fail to secure suitable 

 territory, and in the second, the territory, having been 

 taken, must be held by force, so that only the strongest 

 males remain to mate when the females eventually arrive. 

 So far as one can see, selection is less exacting in the case 

 of the females, which apparently need do little more 

 than respond to the advances of the males. 



With the advent of the females the amorous instincts 

 of the male speedily gather force ; but for their satis- 

 faction it is imperative that the female should be possessed 

 by a like desire. To provoke this, for it is essential to 

 the well-being of the race that offspring should be pro- 

 duced as early as possible, some form of aphrodisiac 

 seems to be necessary. This fact has never been properly 

 realized, though it is implied in Darwin's theory of 

 " Sexual Selection." Here, however, it was used to 

 account for the evolution of resplendent coloration, 

 eccentric postures, and dances which, it was assumed, 

 enabled or induced the female to choose the most 

 mettlesome males. What obtained among sombre- 

 clad species, appears to have excited no curiosity 

 among the students of the evolution theory. Hence 

 it comes somewhat as a surprise to find that the 

 soberly-clad Warblers behave exactly as though they too 

 wore coats of many colours. After what has been said in 

 the last chapter on this head it will be unnecessary to 

 describe these displays among the Warblers in detail, 

 more especially as my friend Mr. Howard has kindly 

 allowed me to use some of the illustrations from his book. 

 These show convincingly enough that the wings and tail 

 are made to play the same part as though they bore all 

 the hues of the rainbow. To bring this fact home com- 

 pare the figures of some of these small birds clad in sober 



