Chapter V 

 SEXUAL SELECTION 



No one can dispute that there is such a thing as sexual selection 

 by battle. The bucks fight for the lordship of the herd, the 

 bull seals to defend their harems from intruders, barndoor cocks 

 for the supremacy of the farmyard. This form of sexual 

 selection is matter of every day observation. But Darwin 

 contended for a great deal more than this. He maintained 

 that in very many species the females chose their mates, and to 

 this source he traced many of the most extraordinary structures 

 found in the higher animals, such as the plumes of the peacock 

 and the bird of paradise. These are among the chefs-d'oeuvre of 

 sexual selection. If, however, we are true Darwinians, we must 

 not begin by studying such superb elaborations, but see first 

 whether in lower classes of animals also there are secondary 

 sexual characters less developed and less conspicuous. Better 

 still will it be if we go to the very base and see whether the 

 differences between the spermatozoon and the ovum correspond 

 in any way to the differences between the sexes. 



Sperma- There is reason to believe that the germ-plasm itself is non- 

 >0 <w!m sex ual, for male characteristics are often transmitted through 

 the female. But the reproductive cells, as distinguished from 

 the germ-plasm which they contain, differ in the most marked 

 way. The male cell is active, the female inactive. In the hydra 

 it is the spermatozoon that breaks loose from its place and goes 

 to seek the ovum. 



The sexes maintain the distinctive characters of the repro- 

 ductive cells. In all species the exceptions are too insignificant 

 to be worth mentioning the male seeks the female, the male 

 is active, the female comparatively sedentary. 



With the greater activity of the male is associated a greater 

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