Media reports on the sex lives of America’s young people often tend more to exaggeration than explanation. Depending on the perspective of the writer, college campuses are portrayed as either sexual Somalias or oases of free love. In their new book Premarital Sex in America: How Young Americans Meet, Mate, and Think about Marrying, sociologists Mark Regnerus and Jeremy Uecker assemble a vast body of research to argue that while today’s sexual culture may be more permissive, it is anything but lawless. Rather, today’s “emerging adults” embrace sex and delay marriage in response to a set of powerful social scripts as comprehensive, and often constraining, as the ideals of courtship that guided their grandparents.

Sex is quite common among emerging adults, though not as common as they generally believe it to be. Among 18- to 23-year-old women currently in non-marital relationships, only 4 percent are not sexually involved with their partner. (The figure for non-involvement is slightly higher for men because fewer men consider their sexual attachments to be relationships.) While these figures seem high, most emerging adults believe that their peers are having sex more often, and earlier, than they really are. This “pluralistic ignorance” is a powerful shaper of sexual behavior, often causing people to engage in sexual practices they might otherwise be reluctant to consider.

Surveys and interviews indicate that emerging adults base their desire to delay marriage on a set of widely shared reasons. Emerging adults describe a desire to “become their own person,” but struggle to express just what this means. Nonetheless, they are notably united in their belief that one’s 20s is a time that should be reserved for experimentation. Related to this is the common “travel narrative,” the belief that one should travel before getting married. People who cite this desire rarely have a specific destination in mind, and few are able to explain just how marriage (which generally reduces expenses and increases resources) nixes travel possibilities.

Emerging adults must balance their ideas of life and love against sometimes harsh realities. Regnerus and Uecker explain the extent to which sexual behavior is determined by the “sexual marketplace.” Their study suggests that where there are more women and fewer men, sex happens more often and with fewer “costs,” like romantic attachment or male commitment.

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The remarkable educational gains made by women—for every 74 men in college in 2005, there were one hundred women—has tipped the sex ratio in favor of the men on campus. A female college student who hasn’t had a relationship in college has an 85% chance of being a virgin if 30% of the student body is female. The same woman on a campus that is 70% female has only a 36% chance of being a virgin. These figures are a significant reflection of the power women wield in sexual relationships, since women are usually (though certainly not always) the partner that seeks to delay intercourse and stands to benefit most from doing so.

The female tilt in the sex ratio extends to the cities and neighborhoods frequented by college-educated young adults. In four zip codes in lower Manhattan, women constitute 78% of all 20-year-olds, declining somewhat over time to a still high 57% of all 30-year-olds. Such an imbalance in the sexual marketplace leads, Regnerus and Uecker report, to “lower levels of relationship commitment, less favorable treatment of women by men, and a more sexually permissive climate wherein women receive less in exchange for sex.”

After looking at these data, Regnerus and Uecker offer a powerful conclusion: the failure of American men to compete academically with their female peers has created a gender imbalance that leaves women at a disadvantage in the sexual marketplace. It is a particularly bitter irony that the societal neglect of the young American male has now become a significant threat to the happiness and well-being of the young American female. If we are to “take back the night,” we may have to first recapture a compelling vision of masculinity that makes education and achievement attractive to a lost generation of young men.

What exactly are the risks of premarital sex? The authors discuss the most well-known and widely feared, including pregnancy and sexually transmitted infection. In the process, they point out the many difficulties of promoting sexual health. Condom usage can be very effective in preventing pregnancy, if done consistently, but typical usage is so haphazard that it is no more effective than the extraction method.

Such are the frustrations of those charged with promoting sexual health, a notion that Regnerus and Uecker argue must be expanded to take account of psychological as well as physical health. They assemble data that shows that “most emerging adults will not experience an unintended pregnancy or an STI, but have already and will continue to experience regrettable sex.”

Indeed, our current preoccupation with keeping sex sanitary, salutary, and unencumbered by anything resembling a moral judgment has led to a narrow focus on preventing pregnancy and sexually transmitted infections, and an effective denial of the regret and depression that follow many sexual encounters. Facing up to the psychological problems associated with casual sex (which are far more common among women) will require the medical profession to decide whether it is possible to withhold judgment without denying necessary care.

Mark Regnerus and Jeremy Uecker gather together (while adding to) a vast body of social science. The picture they draw from the data is one of an age group whose most common sexual practices and social scripts can thwart the relational fulfillment and personal happiness its members seek. A scholarly yet accessible summary of the sexual practices and beliefs of emerging adults, Premarital Sex in America is a book that should be of as much interest and use to students as to their Sociology professors.

Matthew Schmitz is the managing editor of Public Discourse.