264 
THE PRINCIPLES OF 
Part II. 
inequality is greater than with any other animal, for 
during twelve years, out of 6878 births, the male births 
have been as 110*1 to 100 female births. It is, however, 
in some degree doubtful whether it is safe to infer that 
the same proportional numbers would hold good under 
natural conditions as under domestication; for slight 
and unknown differences in the conditions affect to a 
certain extent the proportion of the sexes. Thus with 
mankind, the male births in England are as 104*5, 
in Russia as 108*9, and with the Jews of Livornia as 
120 to 100 females. The proportion is also mysteriously 
affected by the circumstance of the births being legiti- 
mate or illegitimate. 
For our present purpose we are concerned with the 
proportion of the sexes, not at birth, but at maturity, 
and this adds another element of doubt ; for it is a w r ell 
ascertained fact that with man a considerably larger 
proportion of males than of females die before or during 
birth, and during the first few years of infancy. So it 
almost certainly is with male lambs, and so it may be 
with the males of other animals. The males of some 
animals kill each other by fighting; or they drive 
each other about until they become greatly emaciated. 
They must, also, whilst wandering about in eager search 
for the females, be often exposed to various dangers. 
With many kinds of fish the males are much smaller 
than the females, and they are believed often to be 
devoured by the latter or by other fishes. With some 
birds the females appear to die in larger proportion 
than the males : they are also liable to be destroyed on 
their nests, or whilst in charge of their young. With 
insects the female larvrn are often larger than those of 
the males, and would consequently be more likely fo be 
devoured: in some cases the mature females are less 
active and less rapid in their movements than the males, 
