In article <[EMAIL PROTECTED]>,
Wolfgang Rolke <[EMAIL PROTECTED]> wrote:
>2) As for the reason for the observed inequality in birthrates, there
>seem to be several:
> b) Evolution. The argument here seems to be that there is an
>evolutionary advantage to having more boys born than girls, maybe
>because of the higher mortality rate of men. I don't find this argument
>very convincing , mostly because one man can impregnate any number of
>women, and so if anything I would expect this effect to work in the
>opposite direction. Also, it would be amazing to see an evolutionary
>effect to have as subtle an influence as is observed here.
If there is an evolutionary reason, it should be that raising boys is
less costly on average than raising girls. If the costs were the same
and the ratio were unequal, a gene that caused more children of the
less common sex to be born would be selected for, since every child
has one male parent and one female parent.
Higher mortality for males would be relevant only if they die early,
before the parents have invested much in them, making males cheaper to
raise on average. The fact that one man can impregnate many women is
irrelevant. Few men and many women might be advantageous for the
species, but selection for such things takes place at the level of
genes, not species.
These arguments assumes that any advantage is big enough to overcome
any practical difficulties. It could instead be that evolution is
"aiming" at (say) an equal ratio, but for some reason achieving this
exactly is difficult.
I believe that this has been debated extensively in the biological
literature, but I don't have any handy references.
Radford Neal
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