Moral, Physical Disgust Hard-Wired Alike

Feb. 26, 2009 -- Disgust over an unfair or immoral social situation is hard-wired into the human body as strongly as the reaction to a foul taste, according to research published today in the journal Science.

By studying the electrical activity of a muscle in the upper lip in both physically and morally offensive situations, scientists determined that disgust is equally strong in both cases.

"People use the term disgust in terms of morally offensive situations," said Adam Anderson, a professor of neuroscience at the University of Toronto and a co-author on the study. "Our study looked at whether this reaction was genuine disgust or just a metaphor."

At its most basic level, disgust is a physiologic response that keeps a person safe by compelling him or her to spit out contaminated material. Over time, the same response has been adapted to various social situations to offer non-verbal cues that a particular situation is also somehow wrong or unclean.

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The new report is the culmination of four studies spanning several years and involving 80 undergraduates from the University of Toronto.

The first two studies measured students' muscle activity in response to typically physically "disgusting" things: a solution of bitter quinine and images of poop and dirty toilets.

In the next two studies, students played the Ultimatum Game. Simplified, a computer presents a player with many ways to split $10, from fairly (50/50) to unfairly (90/10).

In all four studies scientists stuck electrodes onto the levator labii superioris alaeque nasi, the muscle that curls the upper lip and wrinkles the nose in disgust, to measure electrical activity. The more electrical activity, the greater the lip curl, an indication of greater disgust.

When the Canadian scientists compared the amount of disgust between the first two studies of physical disgust with disgust at immoral or unfair situations, they were able to predict whether a person would accept a particular offer from the computer.