Re: China facing major gender imbalance


"Joe Felsenstein" <joe@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message news:eoeg0p$q0l$1@xxxxxxxxxxxxxxxxxxxxxx
In article <eobakv$nbv$1@xxxxxxxxxxxxxxxxxxx>,
dkomo <dkomo871@xxxxxxxxxxx> wrote:
China facing major gender imbalance

http://www.msnbc.msn.com/id/16593301/?GT1=8921

A great example of how in humans cultural evolution can trump biological
evolution. In most sexually reproducing, diploid animal species normal
evolution keeps the gender ratio adjusted close to 1-to-1. The
explanation of this is a famous result in population genetics, first
worked out by Fisher.

I believe I heard in the recent PBS documentary "China from the Inside"
that the one-child policy in China has been modified so that if the
first child is a girl, couples are permitted to have a second child to
try for a son.

I believe that China is facing a gender imbalance (as is India) because of
selective abortion of female embryos. But this posting implies that
if they follow a policy of trying again when the first child is a girl,
but not otherwise, that this itself will result in a gender imbalance.

This is obvious to everyone, but in fact it is not correct. In fact this
is a famous paradox of probability theory. If you toss a coin, and if you
get tails toss again (but otherwise do not), and if lots of people do that,
the net result is that half of all the tosses are heads and half tails.
No imbalance!

I agree with your analysis of the probabilities. But I think you have
misinterpreted dkomo's point.

If some Chinese, confronted with the single-child national policy,
adopt the practice of selectively aborting female embryos, then an
imbalance will arise with the female birth deficit roughly equal
to the number of females aborted.

However, under the new national policy, some Chinese will allow
first-child females to be born. Even if they still practice selective
abortion on second children, the number of females aborted will be
cut (roughly in half) as will the size of the deficit. And since the
new policy leads to more total births, the deficit as a fraction of
all births is cut by more than half.


.

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