The expressions “you make me sick” and “it left a bad taste in my mouth” may be more than just evocative turns of phrase. A recent study by University of Toronto researchers shows that our sense of moral disgust may have evolved from a basic instinct that helps us distinguish between good and unappetizing tastes and smells.
Hanah Chapman, a PhD candidate with the University of Toronto’s Affect and Cognition Lab, along with Adam Anderson, Joshua Susskind, and David Kim, have found that the facial muscles we use to make an “ugh, gross!” expression when we eat or smell something unpalatable are the same as those we use to express displeasure towards immoral behaviour.
“We were wondering if [moral disgust] is actually the same emotion you feel if you open up Tupperware that’s been in the fridge for too long or step on something nasty on the sidewalk─ or if it was just a powerful metaphor to condemn people’s behaviour,” explains Chapman.
To study whether there is any connection, Chapman and her team studied the facial expressions of people exposed to unappealing tastes, disgusting imagery, and moral transgression using a technique called electromyography, whereby small electrodes are placed on muscles to measure the electrical impulses that occur when they contract.
Chapman’s study measured contractions in the muscle region of the face called the levator labii, the area that raises the upper lip and scrunches up the nose, creating the distinctive “disgusted” expression.
Participants in the study experienced moral transgression when they played the “recipient” in “The Ultimatum Game.” In this game, two participants are given a sum of money and one player is asked to split it. The “decider” may choose to divide it evenly, or may keep a larger proportion of the cash and offer the recipient a smaller sum. The recipient is then free to either accept the offer or reject it and receive no money at all.
“What is interesting is that even though it is in the economic interest of the recipient to accept the offer, when people get offers that are too unequal they’ll reject them because [they are] motivated to punish the other player,” says Chapman.
Chapman and her team found that the levator labii region was consistently stimulated among the recipients when they felt they were being short-changed or treated “immorally.”
“These findings may change the way we think about the human moral impulse,” explains Chapman. “People think of human morality as the pinnacle of human development. What this work shows is that emotions play an important role as well. [Moral] thoughts and judgments are backed up by ancient emotional forces.”
Chapman’s results support Darwin’s contention that the expressions we use to convey emotions evolved from their role in regulating the sensory organs of the face. Reacting to unpleasant tastes and smells by wrinkling our noses and curling our lip may have originally developed to help prevent us from consuming harmful substances such as rotten or toxic food. “It wasn’t until more recently,” says Chapman, “that it was adapted for use in a social context.”
The next step will be to investigate whether this facial expression is learned behaviour or “hardwired” from birth. Chapman and her team plan to test subjects who have been legally blind since early childhood, and haven’t had the opportunity to learn to make the facial expression for disgust in response to social stimulus.
“If they do show it, [that] implies that [the facial expression] happens without learning and that it’s in your genes,” says Chapman. “If they don’t show it, then it’s something you learn from your parents as you grow up.”
