Immoral behaviour really does leave a "bad taste in the mouth" by tapping into an ancient mechanism that helps us avoid poisons and disease, say scientists. Researchers who studied the facial expressions of volunteers found close similarities between their reaction to moral outrage and feelings of "disgust".
A wrinkled nose and curl of the upper lip are classic signs of disgust, an ancient response that evolved to keep people away from infection and danger. It is what causes us to recoil from unpleasant smells and bitter tasting food, or the sight of blood.
In the study in the journal Science, scientists watched the facial movements of volunteers as they sampled bad-tasting liquids or looked at photographs of dirty lavatories or messy injuries. Their reactions were compared with those that occurred when they were treated unfairly in a laboratory game.
Each case produced the same response, marked by a raising of the upper lip and wrinkle of the nose via the levator labii muscle. The research leader, Hanah Chapman, a psychologist at the University of Toronto in Canada, said: "People show activation of this muscle region when tasting something bad, looking at something disgusting, and experiencing unfairness."
Dr Adam Anderson, also from Toronto University, co-authored the study. He said: "Surprisingly, our sophisticated moral sense of what is right and wrong may develop from a newborn's innate preference for what tastes good and bad, what is potentially nutritious versus poisonous."