Chap. VI 11. 



Proportion of the Sexes. 



245 



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 55 

 has advanced what he considers sufficient evidence, with respect 

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

 tant 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, 56 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. 

 Campbell 57 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 sexes of various animals ; and will then briefly 

 discuss how far selection has come into play in determining the 

 result. 



Horses. — Mr. Tegetmeier has been so kind as to tabulate for me from 

 the ' Kacing Calendar ' the births of race-horses during a period of 

 twenty-one years, viz., from 1846 to 1867; 1849 being omitted, as no 

 returns were that year published. The total births were 25,560, 58 con- 

 sisting of 12,763 males and 12,797 females, or in the proportion of 99*7 

 males to 100 females. As these numbers are tolerably large, and as 

 they are drawn from all parts of England, during several years, we may 

 with much confidence conclude that with the domestic horse, or at 

 least with the race-horse, the two sexes are produced in almost equal 

 numbers. The fluctuations in the proportions during successive years 



55 Leuckart (in Wagner ' Hand 

 worterbuch der Phys.' B. iv. 1853 

 8. 774. 



10 Social Science Assoc, of Phila 

 chlphia, 1874. 



57 ' Anthropological 

 April, 1870, p. cviii. 



58 During eleven years a record 

 was kept of the number of mares 

 which proved barren or prematurely 

 slipped their foals ; and it deserves 



Review,' 



notice, as shewing: how infertile 

 these highly-nurtured and rather 

 closely-interbred animals have be- 

 come, that not far from one-third of 

 the mares failed to produce living 

 foals. Thus during 1866, 809 male 

 colts and 816 female colts were born, 

 and 743 mares failed to produce 

 offspring. During 1867, 836 malet 

 and 902 females were born, and 794 

 mares failed. 



