Overall sex ratios were high across all age groups and residency types, but they were highest in the 1-4 years age group, peaking at 126 (95% confidence interval 125 to 126) in rural areas. Six provinces had sex ratios of over 130 in the 1-4 age group. The sex ratio at birth was close to normal for first order births but rose steeply for second order births, especially in rural areas, where it reached 146 (143 to 149). Nine provinces had ratios of over 160 for second order births. The highest sex ratios were seen in provinces that allow rural inhabitants a second child if the first is a girl. Sex selective abortion accounts for almost all the excess males. One particular variant of the one child policy, which allows a second child if the first is a girl, leads to the highest sex ratios.

Conclusions: In 2005 males under the age of 20 exceeded females by more than 32 million in China, and more than 1.1 million excess births of boys occurred. China will see very high and steadily worsening sex ratios in the reproductive age group over the next two decades. Enforcing the existing ban on sex selective abortion could lead to normalisation of the ratios.

Why is this suicidal? Not because China will run out of people. The population will continue to grow. The problem is a social one.

What do you do with all the excesss males?

Presently, the disparity in the cities is not so bad. But with the gradual migration from rural provinces to urban areas that has been taking place the last two decades, that situation will change and social tensions will rise dramatically as males compete for women and jobs. Unrest is virtually guaranteed unless those numbers turn around.

In the past, nations with an excess male population found that putting them in the army and initiating wars of conquest did wonders in eliminating such a disparity. This is unlikely to happen in China but is indicative of the kind of problems such a disparity can cause.

More likely, China will continue enforcing its ban on having more than one child while making it more difficult to have a second child if the first is a girl. This will not please people where the problem is the most pronounced; the rural provinces where there are not only cultural but also supposed practical reasons to have male children helping with the community farm. The prejudice against female babies was so pronounced a few years back that infanticide was a real problem and had to be dealt with severely by the authorities.

Now the problem appears to be selective abortion - a practice that many would argue is no different than infanticide. China, not surprisingly, has very liberal abortion policies and with the state paying for it, has seen a rash of aborting female fetuses in order to try for a male to carry on the family name as well as help out on the farm.

This is a long term problem that bears watching in the west.