[Richard Dawkins]: Sex selection and the shortage of women: is science to blame?

[Lots of interesting food for thought. -egg]

Sent to you via Google Reader

[Richard Dawkins]: Sex selection and the shortage of women: is science to blame?

A couple watch their baby inside a waiting hall at the Nanjing railway station, capital of Jiangsu province. [Reuters/2006]

In nature, the balance of males and females is maintained by natural selection acting on parents. As Sir Ronald Fisher brilliantly pointed out in 1930, a surplus of one sex will be redressed by selection in favour of rearing the other sex, up to the point where it is no longer the minority. It isn't quite as simple as that. You have to take into account the relative economic costs of rearing one sex rather than the other. If, say, it costs twice as much to rear a son to maturity as a daughter (e.g. because males are bigger than females), the true choice facing a parent is not "Shall I rear a son or a daughter?" but "Shall I rear a son or two daughters?"

So, Fisher concluded, what is equlibrated by natural selection is not the total numbers of sons and daughters born in the population, but the total parental expenditure on sons versus daughters. In practice, this usually amounts to an approximately equal ratio of males to females in the population at the end of the period of parental expenditure.

Note that the word 'decision' doesn't mean conscious decision: we employ the usual 'selfish gene' metaphorical reasoning, in which natural selection favours genes that produce behaviour 'as if' decisions are being made.

Interestingly, Fisher's reasoning remains intact, even in harem-based societies such as those of elephant seals, where a minority of males monopolise the females and the majority of males hang about as disconsolate bachelors. From a parent's point of view, a daughter is a 'safe' choice, likely to yield an average number of grandchildren. A son is a high risk choice. He is most likely to give you no grandchildren at all. But if he does give you grandchildren he'll give you lots. The figures balance out and Fisher's equilibrium still holds.

That's what happens in nature. But what if we are dealing with a human society in which cultural traditions over-ride the genetic imperatives (yet another example, this time not necessarily a benign one, of 'rebelling against the selfish genes'). What if the religion of a country fosters a deep-rooted undervaluing of women? What if there is an ancient culture of despising women, whether for religious or otherwise traditional or economic reasons?

In past centuries such cultures might have fostered selective infanticide of newborn girls. But now, what if scientific culture makes it possible to know the sex of a fetus, say by amniocentesis or ultrasound scanning? There is then an obvious temptation selectively to abort female embryos, which could have far-reaching and probably pernicious social c...