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Disgusting - but cool science!

Disgust, distaste, immorality

What is the origin of morality? Some psychologists find its source in our higher cognitive ability. We are offended by immorality because, for example, we adhere to the golden rule, or heed its more self-serving corollary: "What goes around comes around."

But there are hints that morality could have much more ancient roots. For example, our facial response to an immoral situation resembles our response to a bitter taste or the sight of feces, and we sometimes say an unfair deal "leaves a bad taste in the mouth."

Movie courtesy Hanah Chapman, University of Toronto.
Student volunteer shows how the electromyelogram (left) registers activity in the levator labii muscles that lift the upper lip and wrinkle the nose (1.9 Mb QuickTime movie).

A study by Hanah Chapman, a graduate student in psychology at the University of Toronto, published in this week's Science, explores these questions. "We were interested in this conundrum," she says. "People will say they are disgusted by a certain kind of moral offense, but is that the same kind of emotion they feel when they open a take-out container that's been in the fridge too long, or look at a dirty toilet? Or is it a metaphor that we use to condemn the actions of other people?"

Chapman, in concert with her advisor, A.K. Anderson, chose to explore these questions by looking at facial responses to different situations.

Facing the facial expression

Humans the world over use a series of characteristic facial expressions to express basic emotions like anger, sadness, surprise, fear, contempt, happiness and disgust, Chapman says, and their origin has intrigued scientists at least since Charles Darwin wondered whether the bug-eyed expression of fear could widen our field of view to help detect danger.

The core of the stereotypical "disgust" face -- a lifted upper lip and a wrinkled nose -- are both caused by a contraction of the levator labii muscles that run alongside the nose. When these muscles contract in response to a nasty stink, we inhale less odor, Chapman says, so the expression could actually be protective. Chapman and colleagues decided to measure the muscle's activation with standard medical gear called an electromyelogram.

During the experiment, the researchers evoked disgust with sour, salty or bitter drinks, and with photos of feces or injuries. They spurred moral disgust using a game that allows person A to direct the division of $10 with person B. If A gets greedy and asks for, $7 or more, B can reject the deal, leaving both parties empty-handed.

A blonde-red monkey in a zoo's gray rock enclosure bends over and vomits
The reflexive disgust to toxic foods that aided the survival of our primate ancestors may have provided the scaffolding for our complex emotional reactions to dangerous and distasteful social behaviors.
Photo: parislemon
A man with glasses swigs a mystery drink.  Another man winces in disgust, holding his stomach

Discussing disgust

The B's, as you expect, tend to get sad and angry when confronted with a raw deal, but their faces also expressed disgust. When the researchers measured the levator labii, they found a similar level of activation during responses to disgusting drinks, photos and moral choices. Tellingly, as the money offer grew more unfair, activation of the "disgust" muscles increased.

"We were looking for similarities in facial movements across these very different things," says Chapman. "The most basic, primitive form of disgust is thought to be a reaction to things that taste bitter, salty or sour, which can be physically dangerous. Participants also viewed photos of injuries, dirty toilets and insects, which are more abstract than tasting something bitter, but still concrete; these situations pose a danger to the body from disease. And then we also looked at moral disgust, focused on responses to unfairness."

A murder, a bitter drink, and a bad deal can all be called 'disgusting.' Does this mean our moral choices are rooted in our ability to avoid toxic food?

The results, Chapman says, strengthen the idea that moral decisions can involve disgust. "I think this is the best evidence to date that disgust is one of the emotions that people feel in response to moral transgressions." English-speakers tend to confuse anger and disgust, and even brain images cannot clearly distinguish the emotions, she adds. In contrast, facial expression, " is the most specific indication of disgust; people don't wrinkle their noses when they are angry or sad."

However, the study did not exclude all alternative explanations for the correlation, wrote Paul Rozien of the University of Pennsylvania in the same issue of Science, and so does not prove that moral disgust is identical to the primitive feeling of disgust sparked by inedible objects. Still to be proven, he added, is whether " disgust at unfairness is 'the same' as disgust that is elicited through the core route (such as in response to cockroaches)."

- David J. Tenenbaum

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• In Bad Taste: Evidence for the Oral Origins of Moral Disgust, H.A. Chapman et al, Science, Feb. 26, 2009.

•From Oral to Moral (comment), Paul Rozin et al, Science, Feb. 26, 2009.

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