Proponents of ‘broken windows theory’ argue that the men should simply become more law-abiding. Perhaps some do, but even the law-abiding men in these communities do not become marriage-focused; instead, they too become less likely to marry. Why? In their smart book, Too Many Women?: The Sex Ratio Question (1983), the sociologists Marcia Guttentag and Paul Secord explained that a change in sex ratios – the number of men to women in a community – changes the behaviour of the entire group. When men outnumber women, the men compete for the women. They become more eager to marry because otherwise they might be left out of relationships altogether. To do so, they invest more in the things that will attract women: they work harder, they become more faithful, they can become more law-abiding. The women get to choose. Some will prefer higher-earning men; others might prefer better behaved, or funnier, wittier or more attentive men. These traits will then define the norms in the community.

However, when women outnumber men in a community, something very different happens. As a group, the women do not compete harder for the men. Nor do the men aim for higher-status women, at least not if that means the women might outshine them. Instead, men work less hard, become less faithful, and find that they do not need to treat women as well to be able to find at least a temporary partner. Rather than lower their standards, women respond by becoming more likely to give up on the men. They might sleep with them (they still need them to have children after all), but they invest more in themselves, their own income prospects and their own relatives. In short, they make exactly the decisions that women in the communities affected by mass incarceration policies make.