Chap. VIII. SEXUAL SELECTION. 271 



With respect to reptiles and fishes, too little is known 

 of their habits to enable ns to sj)eak of their marriage 

 arrangements. The stickle-back G-asterosteus), however, 

 is said to be a polygamist ; 10 and the male during the 

 breeding-season differs conspicuously from the female. 



To sum up on the means through which, as far as 

 we can judge, sexual selection has led to the develop- 

 ment of secondary sexual characters. It has been shewn 

 that the largest number of vigorous offspring will be 

 reared from the pairing of the strongest and best-armed 

 males, which have conquered other males, with the 

 most vigorous and best-nourished females, which are 

 the first to breed in the spring. Such females, if 

 they select the more attractive, and at the same time 

 vigorous, males, will rear a larger number of offspring 

 than the retarded females, which must pair w r ith the 

 less vigorous and less attractive males. So it will be 

 if the more vigorous males select the more attractive 

 and at the same time healthy and vigorous females ; 

 and this will especially hold good if the male defends 

 the female, and aids in providing food for the young. 

 The advantage thus gained by the more vigorous pairs 

 in rearing a larger number of offspring has apparently 

 sufficed to render sexual selection efficient. But a lame 

 preponderance in number of the males over the females 

 would be still more efficient ; whether the preponder- 

 ance was only occasional and local, or permanent; 

 whether it occurred at birth, or subsequently from the 

 greater destruction of the females ; or whether it in- 

 directly followed from the practice of polygamy. 



TJie Male generally more modified than the Female. — 

 Throughout the animal kingdom, when the sexes differ 



10 



Noel Humphreys, 'River Gardens,' 1857, 



