Re: China facing major gender imbalance

Joe Felsenstein wrote:

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!


What you say is true if the births take place without interference. But
they do not, so the probabilities of a boy or girl are skewed toward
boys. The original policy was to allow only one child, no exceptions.
So couples would would get an ultrasound scan of their fetus at 5
months, and if it was a girl, they'd be more likely to abort it. This
is what led to the gender imbalance in the first place.

With the new policy, the gender imbalance is likely to worsen. Here is
my reasoning. For the first child, the number of girls aborted is
probably going to decrease somewhat because couples would know they have
a "second chance" at a boy.

If the first child is a boy, the couple stops there because they're not
allowed to have a second child. If the first child is a girl, the
likelihood of aborting the second child if the ultrasound shows a girl
will rise dramatically because couples will not want to be "stuck with"
two girl children.

How much the gender imbalance will worsen is a complicated exercise in
conditional probabilities, plus the frequencies of aborting the first
and second girl babies are not known under the conditions of the new
policy. But I think a strong argument can be made that at best, the new
policy will *not* improve the gender balance as long as biased gender
birth probabilities exist.


--dkomo@xxxxxxxx




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Relevant Pages

  • Re: China facing major gender imbalance
    ... couples are permitted to have a second child to ... if they follow a policy of trying again when the first child is a girl, ... that this itself will result in a gender imbalance. ...
    (sci.bio.evolution)
  • Re: China facing major gender imbalance
    ... couples are permitted to have a second child to ... if they follow a policy of trying again when the first child is a girl, ... that this itself will result in a gender imbalance. ...
    (sci.bio.evolution)