Since the numbers are even, everyone can find a partner. But what happens if you take away one man? You might not think this would make much difference. With 20 women pursuing 19 men, one woman faces the prospect of spinsterhood. So she ups her game. Perhaps she dresses more seductively. Perhaps she makes an extra effort to be obliging. That newly single woman then ups her game, too, to steal a man from someone else. A chain reaction ensues. Before long, every woman has to try harder, and every man can relax a little.
Real life is more complicated, of course, but this simple model illustrates an important truth. In the marriage market, numbers matter. And among African-Americans, the disparity is much worse than in Mr Harford's imaginary example. Between the ages of 20 and 29, one black man in nine is behind bars.
For black women of the same age, the figure is about one in For obvious reasons, convicts are excluded from the dating pool. And many women also steer clear of ex-cons, which makes a big difference when one young black man in three can expect to be locked up at some point.
Removing so many men from the marriage market has profound consequences. Why this happened is complex and furiously debated. The era of mass imprisonment began as traditional mores were already crumbling, following the sexual revolution of the s and the invention of the contraceptive pill. It also coincided with greater opportunities for women in the workplace. These factors must surely have had something to do with the decline of marriage. Then, after crunching the census numbers, they found that a one percentage point increase in the male incarceration rate was associated with a 2.
Could it be, however, that mass incarceration is a symptom of increasing social dysfunction, and that it was this social dysfunction that caused marriage to wither? Probably not. For similar crimes, America imposes much harsher penalties than other rich countries. Mr Charles and Mr Luoh controlled for crime rates, as a proxy for social dysfunction, and found that it made no difference to their results.
Similar problems afflict working-class whites, but they are more concentrated among blacks. The collapse of the traditional family has made black Americans far poorer and lonelier than they would otherwise have been.
The least-educated black women suffer the most. Their college-educated sisters fare better, but are still affected by the sex imbalance.
Black women tend to stay in school longer than black men. They are also more likely than white women to seek work. One reason why so many black women strive so hard is because they do not expect to split the household bills with a male provider. And the educational disparity creates its own tensions. If you are a college-educated black woman with a good job and you wish to marry a black man who is your socioeconomic equal, the odds are not good.
She complains about a recent boyfriend, an electrician whom she had been dating for about six months, whose phone started ringing late at night. It turned out to be his other girlfriend. Pressed, he said he didn't realise the relationship was meant to be exclusive. Her advice to single black women is pragmatic: love yourself, communicate better and so on. She says that many black men and women, having been brought up by single mothers, are unsure what role a man should play in the home.
The women expect to be in charge; the men sometimes resent this. Nisa Muhammad of the Wedded Bliss Foundation, a pro-marriage group, urges her college-educated sisters to consider marrying honourable blue-collar workers, such as the postman. But the simplest way to help the black family would be to lock up fewer black men for non-violent offences.
This article appeared in the United States section of the print edition under the headline "Sex and the single black woman". Reuse this content The Trust Project.
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