Hookups: how vague. Dictionaries and sources of Internet wisdom define them as casual sexual encounters, encompassing everything from kissing to intercourse, depending on which source you consult. Somehow, this frustratingly ambiguous term has also come to represent the social mores of a generation: Hookup culture, tastemakers assume, is the universal culture of Millennials.

Not so, says a new study by the Public Religion Research Institute. It surveyed 2300 Americans between the ages of 18 and 35, and found that 37 percent think "sex between two adults who have no intention of establishing a relationship" is morally wrong. Another 21 percent said it depends on the situation. As with any survey, a question this broad inevitably smoothes over nuance—who knows how each respondent interpreted the word "sex," for example, or whether aversions to casualness would soften if there's only a little making out involved. But it also upends assumptions. A majority of young people consider random sex morally wrong in some circumstances, and many of them consider it always wrong. So much for hookup culture.

The researchers purposefully surveyed more blacks, Hispanics, and Asian and Pacific Islanders than they would for a nationally representative poll; what they found is that sexual mores are different among ethnic minorities on a select number of topics. About half of black and Hispanic Millennials disapproved of sex between minors, for example, compared to roughly 40 percent of both whites and Asian and Pacific Islanders. Education also has a big effect: Half of college-educated Millennials are okay with hookups, compared to only a third of those with a high-school degree.