To underline his theory that sexuality is a construct of human discourse, the philosopher Michel Foucault noted that people talk about sex a lot.

“We convince ourselves that we have never said enough on the subject,” he wrote in his (four-volume) “The History of Sexuality.”

After sitting in on a three-hour discussion of sex with 30 students at Northwestern University, on the rainy shore of Lake Michigan, the Economist may have discovered why. Few fields of human behavior — and none more important — are so hard to explain.

Consider the latest evidence that young people in America — as in Japan and some other rich countries — are having much less sex. The portion of Americans aged 18 to 29 who claim to have had no sex for 12 months has more than doubled in a decade — to 23% last year. That is, counterintuitively, despite the removal of many impediments to sex.

Young Americans are less religious and more relaxed about sexual orientation than ever before. They are also readier to experiment, in part owing to the deluge of free porn they receive on smartphones. “You have access to the entire body of porn in your rucksacks!” marveled Alexandra Solomon, a clinical psychologist who runs Northwestern’s renowned “Marriage 101” course, in a subsequent lecture.

Her comment elicited hardly any amusement. Indeed, the most striking thing about the students to an observer from, say, the 1990s, might be how frank and unembarrassable they seem. They were, despite their shared interest in studying sex at an elite university, diverse: straight and gay, black and white, outgoing and reserved. About half were from religious families; a couple from migrant ones. Yet all seemed willing to discuss their sexual likes, dislikes and anxieties, including use of porn, body shyness and the possible role of both in fueling a millennial obsession with pubic grooming. To the extent that they represented their generation, diffidence about sex is not the problem.

The biggest reasons for the “sex recession” are probably straightforward. Married couples have more sex than singletons, and Americans are marrying later. Economic duress is another dampener: It is no coincidence that the slowdown in young Americans’ sex lives began during the Great Recession. Partly as a result of it, many of them still live with their parents. And the low esteem that poor prospects engender, as the experience of many Japanese tragically attests, can also cause mass celibacy.

The recent vigor of America’s economy might make this seem less relevant — especially among high-achievers like the Northwestern students. Yet it was striking how many mentioned the 2008 recession, including their memories of the distress it caused their parents, as a reason to prioritize their careers, even to the extent of forgoing romance entirely. “We’re not looking to get married anymore, so what are we doing?” asked one woman.

But that still does not seem to explain the persistence of America’s sex recession, or its most extreme feature — how concentrated it is among men.

Since 2008 there has been almost a threefold rise in the share of men under the age of 30 who claim to be having no sex. At the same time, the portion of sexless women increased by only 8%. A range of possible explanations for the disparity has been suggested, and the students seemed to corroborate several of them. Many felt men’s social skills had been especially eroded by overreliance on technology. Overindulgence in porn meanwhile offered them an escape route from reality. Yet the most compelling answer, because it contains elements of all that and more, may be signaled by young people’s increasing reluctance to date.

This is often blamed on the “hookup culture” of college campuses. Yet casual sex and dating coexisted in the 1990s. It is also easy to exaggerate — now as then — how many people are hooking up. Half the Northwestern students said they rarely or never did. Yet they also rattled off reasons not to date which, among the men, who would traditionally take the lead in such encounters, included uncertainty about how they were even managed. Many considered the prospect of chatting someone up in a bar not merely daunting but possibly offensive. “Revealing that your intention in talking to someone is sexual? That’s hairy,” shuddered one man.

The problem seems to be a profound anxiety about what the other party to a potential coupling might want and expect. The heavy stress that all the students laid on the importance of mutually agreeing on the basis of any relationship, at every stage of its development, is probably both a cause and effect of this. Dating apps, which around half the students had used, can mitigate it at best. It is likely a response to increased female empowerment, the major change in sexual politics, and therefore further exacerbated by men’s dread of a #MeToo-style harassment charge.

In short, young American men with rather poor interpersonal skills currently face a historically confusing mating-game, even as they worry a lot about their careers. No wonder many are opting to stick to their video games.

This is painful. But it does at least suggest that sexual relations are not so much hitting the skids in America as in flux. The forces that govern sexual behavior are dynamic. Who could have predicted a little more than a decade ago, when George W. Bush was splurging on abstinence schemes, that America would soon see a spike in celibacy fueled by economics, technology, female empowerment and perhaps even casual sex?

Yet that cocktail of circumstances will not last. The economy is strong. The currents in popular culture will shift. And once young Americans become more used to more equal gender relations, they might reembrace the degree of ambiguity and risk that romance entails. That is the hope, at least.

Meanwhile, they might try putting down their phones, talking face to face a bit more. Even flirting.

Copyright 2013 The Economist Newspaper Limited, London. All Rights Reserved. Reprinted with permission.