IN A COLLEGE CAMPUS STUDY in 1989, physically attractive people approached opposite-sex students and asked, “Would you go to bed with me tonight?” Not a single woman said yes, but seventy-five percent of men accepted the invitation. This gender disparity forms the basis of the theory of “sexual economics,” which starts from the familiar premise that most guys want sex to be as easy as possible. Women generally want something else to be provided first, often along the lines of commitment, affection, security, love (perhaps you have heard this list before). These things constitute the “price” of sex for men. The going rate is governed by the norms in a given milieu, in much the same way that housing costs are determined by a local market. Since everyone is keen to (inconspicuously) compare notes, a web of interconnection takes shape so that each transaction has some effect on the marketplace as a whole.

Mark Regnerus and Jeremy Uecker, sociologists both, rely heavily on this theory to explain the sex lives of young adults today. The rise of “the hookup culture” at colleges, they argue, can be attributed in part to the increasing scarcity of men on campus—an oversupply of sellers works to a buyer’s advantage. Sexual economics also suggests that many women look unkindly on promiscuous members of the same sex out of the same impulse that makes retailers angry when Wal-Mart comes to town: they are being undersold, and now they have to give discounts or lose customers.

Regnerus and Uecker are either indifferent or tin-eared about how distasteful this idea is:

Sex might cost little or nothing—a few drinks or some attention and compliments, or simply a promise to be discreet about the liaison. Typically it’s more expensive than that, such as a perceived commitment to being in an exclusive relationship for a while. The highest price a man can pay is a lifetime promise to share all his wealth, income, and affections with a woman exclusively.

Equating an intimate act to a business transaction is not only crass and reductive; it is also analytically misleading. The analogy to commerce implies an adversarial situation wherein the buyer always wants to pay the minimum and the seller wants to get the maximum. But men often find themselves bestowing attention, falling in love, and getting married after they have already been sleeping with the woman in question. Sexual economics has trouble accounting for that. Men willingly overspend, which describes approximately no one who buys a car. Similarly, the pay-for-play hypothesis fails to capture the fact that most women do not want to extract caring and love from a person disinclined to offer it, and they do not see sex as something they wish they could avoid until marriage.