C »AP. VIII. 
SEXUAL SELECTION. 
303 
sufficient evidence, with respect to man and certain 
domesticated animals, to shew that this is one impor- 
tant factor in the result. So again the period of 
impregnation has been thought to be the efficient cause ; 
but recent observations discountenance this belief. 
Again, with mankind polygamy has been supposed to 
lead to the birth of a greater proportion of female 
infants; but Dr. J. Campbell 39 carefully attended to 
ibis subject in the harems of Siam, and lie concludes 
that the proportion of male to female births is the 
Sj tine as from monogamous unions. Hardly any animal 
has been rendered so highly polygamous as oui imglish 
hice-horses, and we shall immediately see that their 
male and female offspring are almost exactly equal in 
dumber. 
Horses. — Mr. Tegetmcicr has been so kind as to tabulate for me 
fr °m 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 have 
been 25, 660,' *“ consisting of 12,763 males and 12,797 females, or in 
the proportion of 99‘7 males to 100 females. As these numbers are 
telerably large, and as they are drawn from all parts of England, 
during several years, we may with much confidence conclude that 
Mtli the domestic horse, or at least with the race-horse, the two 
Se xes are produced in almost equal numbers. The fluctuations in 
the proportions during successive years are closely like those which 
° c cur with mankind, when a small and thinly-populated area is con- 
Adored : thus in 1850 the male horses were as 107T, and m 1807 
only 92'6 to 100 females. Jn the tabulated returns the propor- 
tio ns vary in cycles, for the males exceeded the females during six 
Su ccessive years ; and the females exceeded the males during two 
^ Anthropological Review, April, 18i0, p- cuii. 
40 During the last eleven years a record has been kept of the number of 
*»es which have proved barren or prematurely slipped their foals; and it 
deserves notice, as shewing how infertile these highly-nurtured and rather 
'hsely-interbred animals have become, that not far from one-third of the 
“‘Wes failed to produce living foals. Thus during 1866, 809 male colts 
816 female colts were born, and 743 mares Exiled to produce offspring. 
C^i'iug 1867, 836 males and 902 females were born, and 794 mares failed. 
