A simple theory of sexual disgust

(Warning: Spoilers for The White Lotus, Season 3)

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If you’ve seen season 3 of The White Lotus, you’ll understand why I chose this picture. These are the brothers Lochlan Ratliff (left) and Saxon Ratliff (right), played by Sam Nivola and Patrick Schwarzenegger. While on vacation in Thailand, they have incestuous relations, first kissing each other at the urging of two women they are trying to impress and then going quite a bit further in the middle of a threesome when both are under the influence of powerful party drugs. In the season finale, Lochlan says to Saxon, “I am a pleaser and want to give people what they want.” Since Saxon was being left out of the threesome, Lochlan decided to help his brother out.

There is a lot to say about why many people think what the brothers did was morally wrong. Long ago, the psychologist Jonathan Haidt pointed out the strong disapproval that many have toward incest, even when it’s by consenting adults, suggesting that concerns about purity play an important role in our moral lives. I’ve written about that elsewhere, noting that it’s plausible that our moral disapproval arises, at least in part, because of our revulsion. It’s natural to go from That’s disgusting to That’s wrong.

But let’s focus here just on the revulsion. Here is a headline from The Mirror.

Actually, while we do see the brothers kiss, we never see the “taboo sex scene”; we learn the details when Chloe, the woman in the threesome, talks to Saxon about it while they’re sitting by the pool. The shocked face by another woman in the conversation, Chelsea, has become a popular meme.

Why does this sort of thing repel so many people? And while we’re at it, why are so many of us repulsed by sex acts such as bestiality or sex with corpses, or for some people, sex between men, interracial sex, and masturbation? What’s the best theory of sexual disgust?¹

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We have good theories of disgust in general. The psychologist Paul Rozin is the preeminent researcher on the topic, and, along with his colleagues (including Haidt), he created a disgust scale. Here are some of the items:

—Your friend’s pet cat died, and you have to pick up the dead body with your hands.
—You see a bowel movement left unflushed in a public toilet.
—You discover that a friend of yours changes underwear only once a week.
—You see a man with his intestines exposed after an accident.
—While you are walking through a tunnel under a railroad track, you smell urine.

Your mileage may vary. When I read these aloud in classes and sensations, some people wonder what the fuss is about; others gag; and once, a student ran out of the lecture hall.

These are all instances of what Rozin calls “core disgust”—the sort you get from blood, gore, vomit, feces, urine, and rotten flesh. The best theory of core disgust is that it evolved to ward us away from eating such things. Darwin observed that the facial expression of disgust corresponds to the acts of trying not to smell something, blocking access to the mouth, and using the tongue to expel anything already within. (Actually, the “yuck face” is the same expression one gets when actually retching, and this may be its origin.)

As further evidence for the food theory, the feeling of nausea associated with disgust serves to discourage eating and sometimes leads us to expel foods we’ve already eaten through vomiting. Pregnant women are exceptionally disgust sensitive during the same period that the fetus is most sensitive to poison. And brain areas associated with smell and taste, such as the anterior insular cortex, become active when people are shown disgusting pictures.

Another force in the evolution of disgust might be disease avoidance. Studies find that people around the world are disgusted by pictures depicting people with diseases, such as someone made up to look feverish and spotty-faced. This disease-avoidance theory also captures why the smell of an unwashed stranger can be so repulsive—being unclean is a sign of illness.

But what about sexual disgust? Here are two other items on the scale.

—You hear about a 30-year-old man who seeks sexual relationships with 80-year-old women.
—You hear about an adult woman who has sex with her father.

People report that these activities are disgusting. But they don’t connect in any direct way with eating or disease.

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The immediate response here is that this is obviously explained by evolution. But, no, it isn’t.

Yes, there is a straightforward explanation for why we might want to avoid certain sex acts that either don’t lead to reproduction (such as sex with animals) or don’t lead to the right sort of reproduction (such as sex with parents, siblings, or one’s adult sons or daughters, which can lead to severely impaired children).

But why are we so repulsed when other people engage in these activities? Given mate competition, a good Darwinian would predict that men should have warm and positive feelings towards other men who consistently engage in such activities, as they are, at least temporarily, taking themselves out of the mating market. Looking just at homosexuality, women should be the only ones bothered by gay men, and men should be the only ones bothered by gay women. Plainly, these predictions fail.

What about a cultural theory? Perhaps cultures—including religious communities—somehow inculcate people into being repelled by certain sex acts because they divert members of the community from the sort of reproductively-oriented sex that expands the population. But, again, this makes the wrong predictions. Women, not men, are the limiting factor in the production of children, so this would only explain revulsion toward female sexuality.

A third theory, the most creative of all, is a proposal by Rozin and his colleagues: While core disgust evolved to defend the physical body, it has transformed into a more abstract defense of the soul. People who ignore the sexual boundaries prescribed by our cultures are seen as disgusting and beastly: “Insofar as humans behave like animals, the distinction between human and animals is blurred, and we see ourselves as lowered, debased, and (perhaps most critically) mortal.” Similarly, the philosopher Martha Nussbaum argues that some disgust is “a stratagem adopted to cordon off the dominant group more securely from its own feared animality.” We are disgusted by the Ratliff brothers, then, because their inappropriate sexual activities mark them off as beasts, and such a reminder of our animal nature leads to revulsion.

Creative, but probably not true. It’s way too abstract. It just doesn’t seem likely that the millions of people who turned away when the Ratliff brothers kissed were upset because it reminded them they are animals who will one day die. After all, abstract concerns about animality and mortality don’t lead to revulsion. If they did, then evolutionary trees, diagrams of the double-helix structure of DNA, and funeral homes should make us retch, as they are stark reminders of our finite biological natures.

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I am tempted by a simpler theory, which goes like this: