SEXUAL SELECTION 321 



at birth and for some time subsequently, and owing to the 

 exposure of grown men to various dangers, and to their 

 tendency to emigrate, the females in all old-settled coun- 

 tries, where statistical records have been kept," are found 

 to preponderate considerably over the males. 



It seems at first sight a mysterious fact that in different 

 nations, under difEerent conditions and climates, in Naples, 

 Prussia, Westphalia, Holland, France, England, and the 

 United States, the excess of male over female births is 

 less when they are illegitimate than when legitimate." 

 This has been explained by different writers in many dif- 

 ferent ways, as from the mothers being generally young, 

 from the large proportion of first pregnancies, etc. But 

 we have seen that male infants, from the large size of their 

 heads, suffer more than female infants during parturition, 

 and as the mothers of illegitimate children must be more 

 liable than other women to undergo bad labors, from vari- 

 ous causes, such as attempts at concealment by tight lacing, 

 hard work, distress of mind, etc., their male infants would 

 proportionably suffer. And this probably is the most effi- 

 cient of all the causes of the proportion of males to females 

 born alive being less among illegitimate children than among 

 the legitimate. With most animals the greater size of the 

 adult male than of the female is due to the stronger males 

 having conquered the weaker in their struggles for the pos- 

 session of the females, and no doubt it is owing to this fact 

 that the two sexes of at least some animals differ in size at 

 birth. Thus we have the curious fact that we may attrib- 

 ute the more frequent deaths of male than female infants, 

 especially among the illegitimate, at least in part to sexual 

 selection. 



It has often been supposed that the relative age of the 



*' With the savage Quaranys of Paraguay, according to the accurate Azara 

 ("Voyages dans I'Amerique m&id.," torn, ii., 1809, pp. 60, 119), the women 

 are to the men in the proportion of 14 to 13. 



" Babbage, "Edinburgh Journal of Science," 1829, vol. i. p. 88; also p. 90, 

 on still-born children. On illegitimate children in England, sea "Eeport of 

 Eegistrar General for 1866 ' p. xv. 



