When we were growing up in the early sixties, we could talk about such a thing as “the American family.” A typical family would not differ much whether they were high school dropouts or college grads, whether they lived in Boston or a farm community in Iowa. The marriage rate was high (though it had already started to drop for African-Americans), the median age at first marriage for women was under twenty-one, and children were likely to be raised in two-parent families. College-educated women were somewhat less likely to marry than women with a high school education and somewhat less likely to divorce, but the differences were small.

Today, family trends move in opposite directions for groups separated by class. Only one group in the entire country is more likely to be married at age thirty than in 1970—the women with the top 5 percent of incomes—and the marriage rates of the top 10 percent have not changed. Everyone else is more likely to be single.

For college graduates, divorce rates have fallen back down to the levels of the mid-sixties—before no-fault divorce. At the same time, divorce rates continued upward for other groups, reaching record highs. Non-marital births now exceed 40 percent for the population as a whole. Yet, for white college graduates, they are at 5 percent, up from 2 percent before the financial crisis.

In our last book, Red Families v. Blue Families, we focused on politics and regional differences in the family. We argued that a new “blue” family system had taken hold in the more Democratic states: those states have higher average ages at marriage and lower divorce rates, lower overall fertility and fewer teen births, higher abortion rates and more support for contraception. In contrast, the more Republican states had more voters listing “family values” as a concern and also had families with more children, younger ages at marriage and first birth, and less stable marriages.

These differences corresponded to an ideological gulf among elites: red states have more religious and conservative elites and a working class that attends church less than they do, while blue states have more secular elites and a working class that is more religious than those with higher incomes. Yet we also knew we were seeing something else: blue states are richer, and a big part of the explanation for the demographic differences between red and blue involve wealth.

Rising inequality has fundamentally altered the terms on which men and women find it worthwhile to forge lasting relationships.

In Marriage Markets, we take on the story of class. Rising inequality has affected men more than women; it increased both the number of men at the top eager to pair with high-status women and the number of men at the bottom who no longer play productive roles. These changes fundamentally alter marriage markets—that is, the terms on which men and women find it worthwhile to forge lasting relationships—and they do so in ways that take the top and the bottom of the socio-economic system in different directions.

At the top, increasing disparities among men and among women have made both pickier about potential mates and wary of early commitments that might limit future opportunities. Male executives used to marry their secretaries, who would take care of them at home the way they did in the office. Now both men and women look for mates who enhance their own chances of enjoying the good life, who will be partners in life and in parenting. College graduates still largely forge lasting relationships (typically with one another), but they hedge their bets by delaying marriage and childbearing until they have a better idea of where they (and the partners to whom they commit) are likely to end up—concentrating elite advantage in the process as they overwhelmingly raise their children in financially secure, two-parent families.

The hardest patterns to analyze are those of the middle: the group clustered around the fiftieth percentile of family income in the United States. This group used to be called the “white working class,” but today it is more racially diverse than the comparable group fifty years ago or the college-educated upper third today. Americans in this group have graduated from high school, but lack a B.A. Many started at a university but didn’t finish, or have a community college or vocational degree.

The women from these families in the middle have done well. Unlike the top group, where the sons are more likely to graduate from college than the daughters and the gender gap in income has widened, the women in this group have outpaced the men. They earn higher grades, stay in school longer, and are more likely to return to complete an unfinished degree later in life. When they have the same education and work hours as the men, they have narrowed the gender gap in income.

At the same time, the high-paying manufacturing jobs that once sustained the men in this group have disappeared. With these changing fortunes, the larger group of successful women in the center seeks to pair with a shrinking group of comparable men. Sociologists find that these middle-income women, especially the whites, cycle through more cohabiting partners than any other American women: they move in with a partner, marry, divorce, and cohabit with someone else more often than any other group. For them, changing marriage markets have profoundly changed family patterns.

If we want to understand diverging patterns of family structure, we must be willing to confront the impact of greater inequality.

Ultimately, if we want to understand diverging patterns of family structure, we must be willing to confront the impact of greater inequality on marriage markets—on the way that men and women match up with each other. Our conclusion in Marriage Markets is that the only place where marriageable men outnumber the comparable group of women is at the top, and this ratio reinforces a more stable family culture. At the bottom, chronic unemployment, mass incarceration, violence, and substance abuse reduce the number of available men and make marriage a threat, not an asset, in women’s efforts to provide for their children. Greater protection for fathers’ custodial rights, in turn, lock in the advantages of marriage for elite men and make it more perilous for the women paired with unreliable partners.

The book tells the story of what has happened to the American family, and though the tale is at times complex, the conclusion is short and simple: the economy is central to changing gender expectations and therefore to a culture that supports or undermines family stability. Inequality thus matters to overall social health and it matters to the well-being of future generations. The solutions to changing family structure do not depend on marriage promotion policies. Instead, we should create jobs and greater support for those cycling in and out of increasingly unstable workplaces, and family change will follow.

Naomi Cahn is a law professor at George Washington University and a member of the Homeward Bound project. June Carbone is the Robina Chair of Law, Science and Technology at the University of Minnesota Law School.