SEXUAL SELECTION 289 



and they are eminently polygamous. Thus, according to 

 P^ron, the male sea-elephant of the Southern Ocean always 

 possesses several females, and the sea- lion of Forster is said 

 to be surrounded by from twenty to thirty females. In the 

 North, the male sea-bear of Steller is accompanied by even 

 a greater number of females. It is an interesting fact, as Dr. 

 Gill remarks," that in the monogamous species, "or those 

 living in small communities, there is little difference in size 

 between the males and females; in the social species, or 

 rather those of which the males have harems, the males are 

 vastly larger than the females. ' ' 



Among birds, many species, the sexes of which differ 

 greatly from each other, are certainly monogamous. In 

 Great Britain we see well-marked sexual differences, for 

 instance, in the- wild-duck which pairs with a single female, 

 the common blackbird, and the bull-finch, which is said to 

 pair for life. I am informed by Mr. Wallace that the like 

 is true of the Chatterers or Cotingidre of South America, 

 and of many other birds. In several groups I have not been 

 able to discover whether the species are polygamous or mo- 

 nogamous. Lesson says that birds-of-paradise, so remark- 

 able for their sexual differences, are polygamous, but Mr. 

 Wallace doubts whether he had suf&oient evidence. Mr. Sal- 

 vin tells me he has been led to believe that humming-birds 

 are polygamous. The male widow-bird, remarkable for his 

 caudal plumes, certainly seems to be a polygamist. " I have 

 been assured by Mr. Jenner Weir, and by others, that it is 

 somewhat common for three starlings to frequent the same 

 nest; but whether this is a case of polygamy or polyandry 

 has not been ascertained. 



The Gallinacese exhibit almost as strongly marked sexual 

 differences as birds-of-paradise or humming-birds, and many 



'* The Eared Seals, "American Naturalist," vol. iv., Jan. ISH. 



16 "Tije Ms," vol. iii., 1861, p. 133, on the Progne Widow-bird. See also 

 on the VidvM axillaris, ibid., vol. ii., 1860, p. 211. On the polygamy of the 

 Capercailzie and Great Bustard, see L. Lloyd, "Game Birds of Sweden," 186'?, 

 pp. 19 and 182. Montagu and Selby speak of the Black Grouse as polygamous, 

 and of the Bed Grouse as monogamous. 

 Descent— Vol. I. — 13 



