322 THE DESCENT OF MAN 



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 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 immi- 

 grants, etc. , 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" 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 En- 

 glish race-horse, and we shall immediately see that his male 

 and female offspring are almost exactly equal in number. 

 I will now give the f acts_ 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 "Racing 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," consisting of 

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



** Leuckart (in Wagner, "Hand wbrterbiich der Phys. , " B. iv., 1853, s. 174). 



'5 Social Science Assoc, of Phila., 1874. 



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

 ' '* During eleven years a record was kept of the number of mares which 

 proved barren or prematurely slipped their foals; and it deserves notice, as 

 showing how infertile these highly nurtured and rather closely interbred ani- 

 mals have become, that not far from one-third of the mares failed to produce liv- 

 ing foals. Thus during 1866, 809 male colts and 816 female colts were born, 

 and 743 mares failed to produce offspring. During 1867, 836 males aad 902 

 females were- born, and 794 mares failed. 



