From Our 2009 Archives

Moral Disgust Linked to Primitive Emotion

Study Shows Our Sense of Right and Wrong Has Roots in a Survival Instinct of Early Humans

By Salynn Boyles
WebMD Health News

Reviewed By Louise Chang, MD

Feb. 26, 2009 -- A new study reveals insights into the ancient roots of our modern-day sense of moral disgust.

Research from the University of Toronto suggests that our sense of right and wrong appears to be directly linked to a primitive survival instinct that caused our ancient ancestors to find foul-tasting, poisonous foods disgusting.

The study appears in the Feb. 27 issue of the journal Science.

"These results shed new light on the origins of morality, suggesting that not only do complex thoughts guide our moral compass, but also more primitive instincts related to avoiding potential toxins," principal investigator Adam K. Anderson, PhD, says in a news release.

Morality and Disgust

Morality has been widely considered to be a somewhat recent phenomenon, evolutionarily speaking, that is closely tied to our ability to reason. Disgust, on the other hand, is considered an ancient and primitive emotion, which helped to keep early humans from eating foods that would kill them.

Anderson, lead study author Hanah Chapman, and colleagues conducted a series of experiments designed to determine if morality and disgust are more closely related than experts have thought.

"We wanted to see if there was any truth to the expression, 'It left me with a bad taste in my mouth,' when we talk about something that is morally offensive," Chapman tells WebMD.

"Does that have anything to do with the feeling that you get when you open up that take-out container that has been in the fridge too long or walk into that subway bathroom that hasn't been cleaned in a long time?"

The researchers employed a technique known as electromyography to record electrical activity that directs muscle movements.

They focused on one specific muscle, known as the levator labii, which is involved in raising the upper lip and wrinkling the nose -- movements characteristic of the facial expressions people make in response to disgust.

'More Than a Metaphor'

In one experiment conducted to evoke the most basic, primordial form of disgust, participants drank a bad-tasting bitter liquid. In another, they looked at pictures of things generally recognized as disgusting, like dirty toilets.

In the final test, which measured moral disgust, participants were treated unfairly in a classic psychological experiment.

In all three situations, the participants showed activation of the levator labii muscle, indicating that reactions to tasting something bad, looking at something disgusting, and experiencing unfairness all involved similar disgust.

"People think about morality as being this pinnacle of human evolution and development," Chapman says. "But we showed that this very old and primitive response is playing an important role, too."

Harvard researcher Joshua D. Greene, PhD, tells WebMD that the research is consistent with studies he has done suggesting that emotion plays a key role in moral judgment.

"The idea that the emotion that causes us to reject something poisonous has been co-opted for use in social judgment is certainly intriguing," he says. "This study does not prove this, but it is pretty strong evidence for the idea that disgust in a moral context is more than just a metaphor."

SOURCES: Chapman, H.A. Science, Feb. 27, 2009; vol 323: pp 1222-1226. Hanah Chapman, doctoral candidate, department of psychology, University of Toronto. Joshua D. Greene, PhD, assistant professor, department of psychology, Harvard University. Adam K. Anderson, PhD, Canada Research Chair in Affective Neuroscience, University of Toronto.

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