The single-mother revolution shouldn’t need much introduction. It started in the 1960s when the nation began to sever the historical connection between marriage and childbearing and to turn single motherhood and the fatherless family into a viable, even welcome, arrangement for children and for society. The reasons for the shift were many, including the sexual revolution, a powerful strain of anti-marriage feminism and a “super bug” of American individualism that hit the country in the 1960s and ‘70s.

In its broad outlines, the story is familiar by now. In 1965, 93% of all American births were to women with marriage licenses. Over the next few decades, the percentage of babies with no father around rose steadily. As of 1970, 11% of births were to unmarried mothers; by 1990, that number had risen to 28%. Today, 41% of all births are to unmarried women. And for mothers under 30, the rate is 53%.

Though other Western countries also concluded that it was OK for the unmarried to have kids, what they had in mind as the substitute for marriage was something similar to it: a stable arrangement in which two partners, cohabiting over the long term, would raise their children together. The embrace of “lone motherhood” — women bringing up kids with no dad around — has been an American specialty.

“By age 30, one-third of American women had spent time as lone mothers,” observed family scholar Andrew Cherlin in his 2009 book, “The Marriage-Go-Round.” “In European countries such as France, Sweden and the western part of Germany, the comparable percentages were half as large or even less.”

The single-mother revolution has been an economic catastrophe for women. Poverty remains relatively rare among married couples with children; the U.S. census puts only 8.8% of them in that category, up from 6.7% since the start of the Great Recession. But more than 40% of single-mother families are poor, up from 37% before the downturn. In the bottom quintile of earnings, most households are single people, many of them elderly. But of the two-fifths of bottom-quintile households that are families, 83% are headed by single mothers. The Brookings Institution’s Isabel Sawhill calculates that virtually all the increase in child poverty in the United States since the 1970s would vanish if parents still married at 1970 rates.

Well, comes the response, maybe single mothers are hard up not because they lack husbands but because unskilled, low-earning women are likelier to become single mothers in the first place. The Urban Institute’s Robert Lerman tried to address that objection by studying low-income women who had entered “shotgun” unions — that is, getting married after getting pregnant — on the theory that they represented a population roughly similar to those who got pregnant but didn’t marry. The married women, he found, had a significantly higher standard of living than the unmarried ones. “Even among the mothers with the least qualifications and highest risks of poverty,” Lerman concluded, “marriage effects are consistently large and statistically significant.”

Women and their children weren’t the only ones to suffer the economic consequences of the single-mother revolution; low-earning men have lost ground too. Knowing that women are now expected to be able to raise children on their own, unskilled men lose much of the incentive to work, especially at the sometimes disagreeable jobs that tend to be the ones they can get. Scholars consistently find that unmarried men work fewer hours, make less money and get fewer promotions than do married men.

Experts have come to believe that these are not just selection effects — that is, they don’t just reflect the fact that productive men are likelier to marry. Marriage itself, it seems, encourages male productivity. One study by Donna Ginther and Madeline Zavodny examined men who’d had shotgun marriages and thus probably hadn’t been planning to tie the knot. The shotgun husbands nevertheless earned more than their single peers did.

It’s true that some opportunities — particularly well-paying manufacturing jobs — have declined for men. But a father’s contribution to the family income, even if it’s just $15,000, can dramatically improve the mother’s lot, not to mention that of her — or rather, their — children. And it’s still possible for families to move up to the middle class, despite the factory closings of the last few decades. Ron Haskins of the Pew Center on the States’ Economic Mobility Project puts it this way: “If young people do three things — graduate from high school, get a job and get married and wait until they’re 21 before having a baby — they have an almost 75% chance of making it into the middle class.” Those are pretty impressive odds.

On the other hand, those who opt for single motherhood are hurting not just themselves but their offspring. The children of single mothers are twice as likely as children growing up with both parents to drop out of high school. Those who do graduate are less likely to go to college, even if you control for household income and the mother’s education. Decades of research show that kids growing up with single mothers (again, even after you allow for the obvious variables) have lower scholastic achievement from kindergarten through high school, as well as higher rates of drug and alcohol abuse, depression, behavior problems and teen pregnancy. All these factors are likely to reduce their eventual incomes at a time when what children need is more education, more training and more planning. The rise in single motherhood was ill-adapted for the economic shifts of the late 20th century.

Kay S. Hymowitz, the author of “Marriage and Caste in America,” is a contributing editor at City Journal and a fellow at the Manhattan Institute. This piece is adapted from the spring issue of City Journal.