SELECTION 463 



too, the hen selects that mate which by his song or otherwise 

 excites in greatest degree the mating impulse. Stripped 

 of all its unnecessary aesthetic surplusage, the hypothesis 

 of sexual selection suggests that the accepted mate is the 

 one that most strongly evokes the pairing instinct " (Habit 

 and Instinct, 1896, p. 217). 



It may be insisted, however, that if individual excellence 

 in attractive characters (such as plumes, singing power, 

 dancing agility) does not appeal to the female, it cannot 

 be determinative in preferential mating, and therefore its 

 establishment cannot be effected by any process of sexual 

 selection. Unless the female is somehow aware of the indi- 

 vidual variation in question, the theory breaks down, and 

 yet it is difficult to believe that the female is so meticulous 

 in fastidiousness, so detailed in her preferential excitability. 



The answer, probably sound, is that the details count, not 

 as such, but as contributory to a general impression. Each 

 has its effect, but synthetically, not analytically. " Even 

 when the female seems to choose some slight improvement 

 in colour or song or dance, the probability is that she is 

 simply surrendering herself to the male whose tout ensemble 

 has most successfully excited her sexual interest " (Geddes 

 and Thomson, Evolution, 1911, p. 172). 



(h) If one provisionally accepts the theory that a sec- 

 ondary sex-character may have been established and aug- 

 mented because it contributed to a decision in preferential 

 mating, one has to face the further question of the signifi- 

 cance or racial justification of the courtship-habits often so 

 prolonged, elaborate, and exhausting. The sifting probably 

 works well in keeping up a standard of racial fitness, for 

 the most persuasive male is likely to be, among animals, 

 the fittest all round. But there is surely more than this, 



