PROPORTION OF THE SEXES. 239 



excess of male over female births is less when they are illegitimate 

 than when legitimate."* This has been explained by different 

 writers in many different ways, as from the mothers being gener- 

 ally young, from the large proportion of first pregnancies, &c. 

 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 various causes, 

 such as attempts at concealment by tight lacing, hard work, dis- 

 tress of mind, &c., their male infants would proportionally suffer. 

 And this probably is the most efficient of all the causes of the 

 proportion of males to females born alive being less amongst 

 illegitimate children than amongst 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 ani- 

 mals 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 amongst 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 evidence, with respect 

 to man and certain domesticated animals, that this is one im- 

 portant 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 observa- 

 tions discountenance this belief. According to Dr. Stockton- 

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

 parents, residence in the country or in cities, the crossing of 

 foreign immigrants, &c., all influence the proportion of the sexes. 

 With mankind, polygamy has also been supposed to lead to the 

 birth of a greater proportion of female infants ; but Dr. J. Camp- 

 bell"' carefully attended to this subject in the harems of Siam, 

 and concludes that the proportion 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 are 

 almost exactly equal in number. I will now give the facts which 

 I have collected with respect to the proportional numbers of the 



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

 p. 90, on still-born children. On illegitimate children in England, see 

 'Report of Registrar-General for 1866,' p. xv. 



=6 Leuokart in Wagner 'Handworterbuch der Phys.' B. Iv. 1853, s. 774. 



»» Social Science Assoc, of Philadelphia, 1874. 



" 'Anthropological Review,' April, 1870, p. cviii. 



