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.

In terms of their relationships, 71 percent of Millennials felt that marriage is still a relevant institution (although more black and Hispanic young people said marriage is "old-fashioned and out of date" compared to whites and Asians). Remarkably, 44 percent of Hispanic young people said that families suffer if women have full-time jobs, compared to a third or less of other ethnic groups. About half of all respondents said it's fine if one person in a relationship takes on most of the household chores—perhaps imagining they'd be the one freed from dish duty forevermore.

These trends are fascinating in the context of Millennials' religious beliefs. A third of those aged 18 to 35 don't affiliate with any religion, be they atheist, agnostic, apathetic, or just not anything in particular. Compared to their parents and grandparents, Millennials are much less white and much less Christian—only a third identify as white Christians, compared to 68 percent of those over 65. Religious conservatism among American young people certainly isn't dead, but it's changing shape; at the very least, it doesn't seem like an adequate explanation for the traditional attitudes Millennials have adopted toward sex relationships.

The moral lives of Millennials, it turns out, are more complex than the media likes to think. They're much more likely to favor gay marriage and legal pot than their parents and grandparents, but mirror their views about abortion. Teen pregnancy is dropping; looking now at their younger peers, many Millennials wish they wouldn't have sex. And told that they are part of a pervasive culture of casual sexual encounters, many Millennials say: That's not for me—or, at least, it depends. Their politics and mores don't fit neatly on a spectrum from conservative to liberal—and perhaps that's fitting for a generation of Americans who are more diverse than any before.