A. S. PARKES 
males in the lower age groups would pair off with the surplus 
females in the higher age groups, many of whom, of course, must 
be widows. ‘This again is not likely to happen on any large scale. 
What is going to happen, according to the demographers, is 
that the excess males will find their females not by going after 
widows, but by robbing younger age groups of females. This, 
of course, would set up a chain reaction so that males would 
necessarily seek younger and younger females. The existing 
situation is only a foretaste of what may come if and when a 
large excess of males appears at marriageable age, and the 
logical conclusion of the expert view is that oldish men will be 
bespeaking newly born females. 
We must now consider the biological aspects and implications 
of the probability that there is a large excess of males at con- 
ception. First, how is this explicable in the light of the chromo- 
some mechanism of sex determination, which implies the con- 
ception of equal numbers of males and females? There are two 
obvious possibilities. One is that in spite of the chromosome 
mechanism, the actual production of normal functional sperma- 
tozoa is not in the ratio of 1:1, and the other is that the Y male- 
producing spermatozoa have some advantage over the X female- 
producing spermatozoa in the female tract, so that a larger 
number reach the site of fertilization. One or other of these 
possible factors operates to produce the male excess at concep- 
tion unless there is some less obvious cause. 
The second point of biological interest is the evolutionary 
significance of the high ratio at conception. It might be said, 
perhaps, to have the purpose of allowing for subsequent male 
loss and so maintaining the ratio among adults at 1:1. But 
what, in fact, is the evolutionary value to mammals of such a 
ratio? Surely numerical equality between the sexes is a hang- 
over from those lower vertebrates in which the reproductive 
potential of the two sexes was nearly equal and in which there- 
fore equal numbers of the sexes were required for maximum re- 
productivity. On this view, the 1:1 ratio in mammals is some- 
thing of a biological anachronism. With thevery largedifference 
in the reproductive potential of the two sexes, a sex-ratio of 
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