In 2013, young American women face a new and unexpected form of oppression by men.

It's not in the arenas we're accustomed to: the workplace — where young women in major American cities now routinely make more money than young men do — or education, where women earn close to a whopping 60 percent of college degrees.

It's the widespread social practice of cohabitation, which has exploded 14-fold since 1970, when the sexual revolution kicked into high gear. Back then for women, the freedom to cohabit without marriage — without risking social disapproval — was regarded as a potent symbol of sexual equality. Prominent feminists viewed marriage with suspicion, portraying it as a patriarchal ball and chain.

Today, we take cohabitation for granted. We think of living together before marriage as an equal-opportunity chance for a couple to test if they're right for each other long-term. It's becoming clear, however, that for many women cohabitation is the real ball and chain.

A new paper from the RAND Corporation confirms that women and men tend to have significantly different expectations of cohabitation — that men are, on average, significantly less committed.

According to the paper, 52 percent of cohabiting young men ages 18 to 26 indicate uncertainty about whether their relationships will last, compared with only 39 percent of cohabiting women that age. More than four in 10 men say they are not "completely committed" to their partners, compared with only 26 percent of women. (Among married couples, only 19 percent of both men and women say that they are not "almost certain" their relationship is permanent.)

Cohabiting men's lack of commitment manifests itself in other ways. For example, they are significantly more likely than their female partners to maintain a separate residence. In fact, male cohabitors "broadly report lower levels of relationship intensity than female cohabitors" on all measures the paper assessed, including consolidation of resources, intimacy and commitment.

Most of us have seen examples of this. We know a young woman — or two or three — who's lived with a guy, hoping for "together forever," while he takes his time deciding whether to commit. Three years later, he announces that he's "not ready" for marriage. He walks away with few regrets, but she's left, at age 32, with a ticking biological clock and the uphill task of finding a man who will promise to love and stand by her forever.

What's going on here? The Wall Street Journal's James Taranto calls it "a disequilibrium in the romantic marketplace." "The tendency," he notes, "is for women to be more committed than men, which suggests that many women settle for cohabitation when they would prefer marriage."

In 2013, young people are still forming couples at about the same rate as 40 years ago. But the marriage rate is plummeting. Today, data suggest that roughly half of young women have cohabited by age 24, and about 70 percent by age 30.

The RAND paper's findings seem to confirm that women, more than men, tend to value the stability, economic security, and fidelity that marriage generally brings. Before the sexual revolution, society supported women who wanted this for themselves and their children by encouraging marriage and discouraging cohabitation. Ironically, the sexual revolution shifted power on this front from women to men.

Children are also big losers. Why? Cohabiting couples with a child are more than twice as likely to break up as are married parents. Cohabiting couples report more violence and conflict and lower levels of satisfaction. Children who reside with their mother and her boyfriend are about 11 times more likely to be sexually, physically or emotionally abused — and six times more likely to be neglected — than children living with their married biological parents. Children of cohabiting biological parents are four times more likely to be abused than are their peers with married biological parents.

It's no surprise, then, that children in cohabiting situations are more likely to experience drug use, teen pregnancy, delinquency, school failure and depression than are children in intact, married families.

We've grown used to thinking of divorce as the greatest threat to the stability of the American family. But cohabitation has now assumed that role.

Today, the divorce rate for married couples with children has fallen almost to the levels of the early 1960s. However, about 24 percent of children are born to cohabiting parents, and an additional 20 percent live in a cohabiting household at some point during their childhood.

That's bad for everyone: women, children — and men as well.

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Katherine Kersten is a senior fellow at the Center of the American Experiment. The views expressed here are her own. She is at kakersten@gmail.com.