SEL UAL SEL EUTION. 249 



marked sexual differences. I asked Mr, Bartlett, of the 

 Zoological Gardens, who has had r-?ry large experience 

 with birds, whether the male -cragopan {one of the Gallin- 

 acea?) was polygamous, and I was struck by his answering, 

 "I do not know, but should think so from his splendid 

 colors." 



It deserves notice that the instinct of pairing with a single 

 female is easily lost under domestication. The wild-duck 

 is strictly monogamous, the domestic duck highly polyga- 

 mous. The Rev. W. I). Fox informs me that out of some 

 half- tamed wild ducks, on a large pond in his neighbor- 

 hood, so many mallards were shot by the gamekeeper that 

 only one was left for every seven or eight females; yet 

 unusually large broods were reared. The guinea-fowl is 

 strictly monogamous; but Mr. Fox finds that his birds suc- 

 ceed best when he keeps one cock to two or three hens. 

 Canary-birds pair in a state of nature, but the breeders in 

 England successfully put one male to four or five females. 

 I have noticed these cases as rendering it probable that 

 wild monogamous species might readily become either tem- 

 porarily or permanently polygamous. 



Too 'little is known of the habits of reptiles and fishes 

 to enable us to speak of their marriage arrangements. The 

 stickle-back (Gasterosteus), however, is said to be a polyg- 

 arnist;* 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 development of second- 

 ary sexual characters. It has been shown that the largest 

 number of vigorous offspring will be reared from the pair- 

 ing of the strongest and best-armed males, victorious in 

 contests over other males, with the most vigorous and best- 

 nourished females, which are the first to breed in the spring. 

 If such females select the more attractive, and at the same 

 time vigorous males, they will rear a larger number of off- 

 spring than the retarded females, which must pair with 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 espe- 

 cially hold good if the male defends the female and aids 

 in providing food for the young. The advantage thus 



*tf oei Humphreys, " Eiver Gardens," 1857. 



