148 THE COURTSHIP OF ANIMALS 



and the same is true, though perhaps in less extent, with 

 the females ; hence, then, it is clear display is a product of 

 sexual selection. 



That sexual desire is less intense in the case of the 

 females is to be regarded as another result of this form 

 of selection. If they displayed the same intensity of 

 passion the males would speedily become exhausted, 

 for it is well known that the gratification of the sexual 

 emotions is far more enervating in the case of the male. 

 It may well be that polyandry has arisen from this 

 transference to the females, or development by the females, 

 of increased sexual hunger. 



The fact that birds will repeat, albeit imperfectly, the 

 phases of the sexual display under the stimulus of fear, 

 or anger, and when no females are present, must be 

 regarded as an indication, for we can scarcely call it a 

 proof, that exaggerated movements have become the 

 normal concomitants of great excitement, at any rate 

 during the season of reproductive activity. They are 

 purely nervous responses to external conditions. It must 

 not be forgotten that, at this time, fear begets other 

 movements, equally striking, such as feigning lame- 

 ness, and death, which have no part in the sexual 

 display. 



Interpreted in this light one can understand that to 

 the female not as yet sexually " ripe " or sexually 

 " hungry," these movements, when not interpreted as 

 signs of fear or anger, fail to produce any response. So 

 soon, however, as this period of " ripeness " arrives, the 

 stimulus through the nervous system produces the desired 

 response, begetting a complementary stimulus through 

 the secretions of the sexual glands, by what we may call 

 the flow of the hormones ; just as the sight of food 



