PROPORTION OF THE SEXES. 277 



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 liahle 

 than other women to undergo bad labors, from various 

 causes, such as attempts at concealment by tight lacing, 

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

 proportionately 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 possession 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 attribute 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 

 two parents determines the sex of the offspring; and Prof. 

 Leuckart * has advanced what he considers sufficient evi- 

 dence, with respect to man and certain domesticated 

 animals, that this is one important though not the sole 

 factor in the result. So again the period of impregnation 

 relatively to the state of the female has been thought by 

 some to be the efficient cause; but recent observations dis- 

 countenance this belief. According to Dr. Stockton 

 Hough, f the season of the year, the poverty or wealth of 

 the parents, residence in the country or in cities, the cross- 

 ing of foreign immigrants, etc., all influence the proportion 

 of the sexes. With mankind, polygamy has also been sup- 

 posed to lead to the birth of a greater proportion of female 

 infants; but Dr. J. Campbell J carefully attended to this 

 subject in the harems of Siam, and concludes that the pro- 

 portion of male to female births is the same as from 

 monogamous unions. Hardly any animal has been rendered 

 so highly polygamous as the English race-horse, and we 

 shall immediately see that his male and female offspring 



* Leuckart, in Wagner, " Handworterbuch der Pliys,," B.iv, 1853, 

 s. 774. 



f Social Science Assoc. of Philadelphia, 1874. 

 j " Anthropological Review," April, 1870, p. 108, 



