Watch Out

Nevertheless, den Boer and Hudson do advance a somewhat trenchant feminist argument, buttressed by rather selective use of historical examples. Men are inherently aggressive by nature, they say. They have a far greater propensity towards criminal behaviour. Therefore, any society with a marked excess of males (such as the Wild West of 19th-century America) is likely to be violent and lawless.

“We are not suggesting that a country with a high male-to-female sex ratio will necessarily be a violent society,” den Boer says. “And having equal numbers of men and women certainly doesn’t guarantee peace. Rwanda has a normal sex ratio. But it is a biological fact that males have testosterone in a quantity that isn’t present in females. And I think that if you have large numbers of surplus males who are of low socioeconomic status, who have little stake in their country and who are given few opportunities to improve their status, then they will exhibit aggressive behaviour patterns.”

How might governments deal with the problem? Den Boer and Hudson outline several fairly benign ways in which the potential destructive force of bare branches might be defused. Surplus males could be exported to countries that need more workers. Or poor women from other countries might be attracted to China in search of better-off husbands (though a more likely scenario would surely be a vast increase in prostitution and the trade in sex slaves).

Or the Chinese Government could inaugurate big infrastructure projects, particularly in the underdeveloped west — pipelines, dams — that would provide employment (though not female mates) for large numbers of young men, well away from cities, where they might cause trouble. Better still, governments could step up efforts to improve women’s social and economic status, so that bringing a daughter into the world ceased to be seen as a financial calamity.

But the authors also discuss far more sinister options for “soaking up” excess males. One — which seems to have rattled Western strategists to such an extent that both authors have been interviewed by the CIA — is that China could greatly increase the size of its army and then provoke a confrontation (with Taiwan, for example) that would result in heavy casualties . “In addition to stimulating a steadier allegiance from bare branches, who are especially motivated by issues involving national pride and martial prowess,” the authors write, “conflict is often an effective mechanism by which governments can send bare branches away from population centres, possibly never to return.”

Having outlined this apocalyptic scenario, however, the authors now seem keen to downplay it. “The idea of China raising an enormous army and then sending it off to fight some battle is one of the least likely options,” says den Boer. “Much more possible, particularly if the economy takes a downward turn, is a scenario in which bare branches cause so much social instability, so much internal violence, that the Chinese government is forced to become very authoritarian again, and increase its internal security forces. Or it might tolerate internal conflict, simply to allow some of these young men to self-destruct. Either way, we should be worried about the instability of such a large population.”

We should. Particularly if (as China’s latest census suggests) we are seeing only the first stage of the Asian male-population explosion. Bare Branches may overstate its case. But if its melodramatic assertions shock the world into recognition of an astonishing phenomenon that has hitherto hardly been noticed outside specialist circles, it will have done us all a service. After all, two fifths of the human race live in China or India. If there is even a small chance of those teeming populations being destabilised by a skewed birth-rate, we should all be worried.

Bare Branches is published by the Massachusetts Institute of Technology Press.

Do bare branches pose a threat? E-mail debate@thetimes.co.uk