A FEW years ago it looked like the curse that would never lift. In China, north India and other parts of Asia, ever more girls were being destroyed by their parents. Many were detected in utero by ultrasound scans and aborted; others died young as a result of neglect; some were murdered. In 2010 this newspaper put a pair of empty pink shoes on the cover and called it gendercide. In retrospect, we were too pessimistic. Today more girls are quietly being allowed to survive.

Gendercide happens where families are small and the desire for sons is overwhelming. In places where women are expected to move out of their parents’ homes upon marriage and into their husbands’ households, raising a girl can seem like an act of pure charity. So many parents have avoided it that, by one careful estimate, at least 130m girls and women are missing worldwide. It is as if the entire female population of Britain, France, Germany and Spain had been wiped out.

Fortunately, pro-girl evangelising and economic growth have at last begun to reverse this terrible trend (see article). Now that women are more likely than before to earn good money, parents see girls as more valuable. And the craving for boys has diminished as parents realise that they will be hard to marry off (since there are too few brides to go around). So the imbalance between girls and boys at birth is diminishing in several countries, including China and India. In South Korea, where a highly unnatural 115 boys were being born for every 100 girls two decades ago, there is no longer any evidence of sex selection—and some that parents prefer girls.

This is wonderful news, and it will be still more wonderful if the progress continues. Ending the war on baby girls would not only cut abortions, which are controversial in themselves and can entail medical complications, especially in poor countries. It would also show that girls and women are valued. Yet gendercide will leave an awful legacy. Today’s problem is a shortage of girls; tomorrow’s will be an excess of young men.

As cohort after cohort of young Asians reach marriageable age, all of them containing too few women, a huge number of men will struggle to find partners. Some will import foreign brides, thereby unbalancing the sex ratio in other, poorer countries. A great many will remain single. Some women will benefit from being more in demand. But the consequences are bad for societies as a whole, because young, single, sex-starved men are dangerous. Stable relationships calm them down. Some studies (though not all) suggest that more unattached men means more crime, more rape and more chance of political violence. The worst-affected districts will be poor, rural ones, because eligible women will leave them to find husbands in the cities. Parts of Asia could come to resemble America’s Wild West. (Many polygamous societies already do: think of Sudan or northern Nigeria, where rich men marry several women and leave poor men with none.)

There are no easy answers. Historians note that rulers used to deal with surpluses of young men by sending them off to war, but such a cure would obviously be worse than the disease. Some say governments should tolerate a larger sex industry. Prostitution is often lawless and exploitative, but it would be less so if governments legalised and regulated it. One Chinese academic has suggested allowing polyandry (ie, letting women take more than one husband). In the most unbalanced areas something like this may happen, regardless of the law.

Don’t just do something

Above all, governments should be cautious and humble. When trying to strong-arm demography, they have an awful record. China’s one-child policy, though recently relaxed, has aggravated the national sex imbalance—and been coercive, brutal and less effective than its admirers claim. Without it, the birth rate in China would have fallen too—perhaps just as fast. Bad policies often outlast the ills they are supposed to remedy.

It will be for Asian societies to deal with the excess male lump they have created. It would help if they did not look down on bachelors: some make it hard for unmarried people to get hold of contraceptives. But whatever policymakers do now, the sex imbalance will cause trouble for decades. The old preference for boys will hurt men and women alike.