Why So Many People Care So Much About Others' Sex Lives

A new study looks at the evolutionary psychology behind ideas of sexual morality.

Here’s a loaded question: Is casual sex immoral?

From Hester Prynne to Hobby Lobby, from our dorm-mates to our politicians, it’s an issue that’s sparked more than its fair share of fiery public debate (after all, we Americans are a judge-y people). A recent study done by researchers at Cornell and New York University summed it up this way: Casual sex is psychologically good for you if you if think it’s acceptable, but not if you don’t.

So the answer, clearly, depends on who’s being asked—but odds are that either way, they won’t feel tepid about it.

Your answer may depend, at least in part, on where your money comes from (if you’re a woman) or where it goes (if you’re a man). At least, that’s the argument of a paper recently published in The Archives of Sexual Behavior, which found that promiscuity—by both men and women—is more likely to be considered a moral violation in places where women are economically dependent on men.

Researchers from Brunel University took participants’ temperatures on casual sex by asking them to rate their agreement with statements like “Promiscuous women are not worthy of much respect” and “It is fine for a woman to have sex with a man she has just met, if they both want to.” (The participants, all Americans, also scored the statements with the genders reversed). Another survey measured their perceived prevalence of women’s financial reliance on men (sample statement: “Most women I know depend heavily on the money of a male partner, or probably will at some point in their life”).

Even after controlling for variables like age, religiosity, and political affiliation, the study authors found that people who saw female financial dependence on men as more common were also more likely to negatively judge promiscuity in both sexes.

One possible reason for this correlation boils down to some pretty old-school reproductive math:

In environments in which female economic dependence on a mate is higher, both a woman and her mate have a greater interest in maximizing paternity certainty. Because promiscuity undermines paternity certainty, both men and women should be more opposed to promiscuity by both sexes.

We’ve evolved to consider sex, the researchers argue, as a game of finite resources. For our ancestors, multiple sexual partners meant things could get knotty when it came to proving whose kids were whose. For women who depended on men for their livelihoods (and the livelihoods of their offspring), that uncertainty meant losing out on the support of their male partners. Bad news. For men, it meant investing in the well-being of children they hadn’t necessarily fathered. Also bad news.

The connection between sexual behavior and morality, then, may have come about as a way of keeping a gender-based social order intact. “Through moralizing,” the researchers wrote, “individuals can promote behavior which serves their own personal and coalitional interests.” Back in the day, judgment was a form of defense.

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Cari Romm writes for and produces The Atlantic's Health Channel.

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