THE SEXUAL SELECTION THEORY 155 



stimulating secretions of the ancillary sexual glands, the 

 hormones of the pituitary and thyroid, or the primary 

 glands — testis and ovary— decreases fertility, or induces 

 sterility. Where these stimulants are lacking there will 

 be no desire, no display, and no pairing, and consequently an 

 end to this defective strain. Here then is Sexual Selection. 



Instances of such impotency on the part of either sex 

 are wanting, and we can only speculate as to how such 

 cases would be met. Would a female who had chanced 

 to settle in the territory of a male whose sexual impulses 

 carried him no further than seizing territory remain 

 with him throughout the mating season, held by an 

 imperfectly roused, ill-defined, sexual instinct ? Or, 

 eventually becoming mate-hungry, and failing to stimulate 

 him to perform his part, would she desert him and seek 

 another mate ? On the other hand, would a male, failing 

 to arouse response in the female he had secured, drive her 

 away and supplant her ? 



In other words, are we then justified in postulating 

 differential effects in regard to display : a minimum of 

 intensity to ensure mating ? A display of some sort is 

 essential. It may be feeble as compared with that of 

 another species — that of the Sparrow, for instance, com- 

 pared with that of the Peacock — but it must be sufficiently 

 good of its kind to effect its purpose, which is to " hustle " 

 up the production of offspring. A phlegmatic but virile 

 male, or a too feeble performer, is almost as certainly 

 doomed to extinction as an impotent male; for his 

 offspring will probably be eliminated by the adverse 

 conditions of existence to which their late appearance 

 exposed them. Where a female settles down with a 

 male which does not attain to the standard of display 

 characteristic of his race, it is conceivable she may sooner 



