the link between physical and moral disgust -- 6/1/23

Today's encore selection -- from This Is Your Brain on Parasites by Kathleen McAuliffe. Revulsion and disgust at physical things -- such as overflowing toilets -- shares much of the brain's circuitry with moral outrage. Both are associated with the brain's anterior insula and amygdala. This may explain why moral judgments are so often coupled with disgust:

"Visceral disgust -- that part of you that wants to scream 'Yuck!' when you see an overflowing toilet or think about eating cock­roaches -- typically engages the anterior insula, an ancient part of the brain that governs the vomiting response. Yet the very same part of the brain also fires up in revulsion when subjects are outraged by the cruel or unjust treatment of others. That's not to say that visceral and moral disgust perfectly overlap in the brain, but they use enough of the same circuitry that the feelings they evoke can sometimes bleed together, warping judgment.

"While there are shortcomings in the design of the neural hardware that supports our moral sentiments, there's still much to admire about it. In one notable study by a group of psychiatrists and political scien­tists led by Christopher T. Dawes, subjects had their brains imaged as they played games that required them to divide monetary gains among the group. The anterior insula was activated when a participant de­cided to forfeit his own earnings so as to reallocate money from players with the highest income to those with the lowest (a phenomenon aptly dubbed the Robin Hood impulse). The anterior insula, other re­search has shown, also glows bright when a player feels that he has been made an unfair offer during an ultimatum game. In addition, it's activated when a person chooses to punish selfish or greedy players.

"These kinds of studies have led neuroscientists to characterize the anterior insula as a fountainhead of prosocial emotions. It is credited for giving rise to compassion, generosity, and reciprocity or, if an in­dividual harms others, remorse, shame, and atonement. By no means, however, is the insula the only neural area involved in processing both visceral and moral disgust. Some scientists think the greatest overlap in the two types of revulsion may occur in the amygdala, another an­cient part of the brain.

"Psychopaths -- whose ranks swell with remorseless cold-blooded killers -- are notorious for their lack of empathy, and they typically have smaller than normal amygdalae and insulae, along with other ar­eas involved in the processing of emotion. Psychopaths are also less bothered than most people by foul odors, feces, and bodily fluids, tol­erating them -- as one scientific article put it -- 'with equanimity.'

"People with Huntington's disease -- a hereditary disorder that causes neurological degeneration -- are similar to psychopaths in hav­ing shrunken insulae. And they, too, lack empathy, though they don't exhibit the same predatory behavior. Possibly owing to damage to ad­ditional circuits involved in disgust, however, the afflicted are remark­able in showing no aversion whatsoever to contaminants -- for exam­ple, they think nothing of picking feces up with their bare hands.

"Interestingly, women rarely become psychopaths -- the disorder affects ten males for every one female -- and they have larger insulae than men relative to total brain size. This anatomical distinction may explain why they're the sex most sensitive to disgust, and it may also have bearing on yet another traditionally feminine characteristic: as befits women's role as primary caretakers, they score higher than men on tests of empathy -- a very useful trait for gauging when a cranky baby has a fever or needs a nap.

"Why moral and visceral disgust became entangled in our brains in the first place is harder to explain, but British disgustologist Val­erie Curtis puts forward a scenario that, while impossible to verify, certainly sounds plausible. Evidence from prehistoric campsites, she notes, suggests that our ancient ancestors may have been more con­cerned about hygiene and sanitation than commonly assumed. Some of the earliest artifacts from these sites include combs and middens (designated dumpsites for animal bones, shells, plant remnants, hu­man excrement, and other waste that might attract vermin or preda­tors). Early humans, she strongly suspects, would have taken a dim view of peers who were slobs about disposing of their garbage, spat or defecated wherever they pleased, or made no effort to comb the lice out of their hair. These inconsiderate acts, which exposed the group to bad odors, bodily waste, and infection, triggered revulsion, and so, by association, the offenders themselves became disgusting. To bring their behavior into line, Curtis thinks, they were shamed and ostra­cized, and if that failed, they were shunned -- which is exactly how we react to contaminants. We want nothing to do with them.

"Since similar responses were required to counter both types of threat, the neural circuitry that evolved to limit exposure to parasites could easily be adapted to serve the broader function of avoiding peo­ple whose behavior endangered health. Complementing this view, Curtis's team found that people who are the most repulsed by unhy­gienic behavior score higher than average on a test of orientation to­ward punishment -- that is, they are the most likely to endorse throwing criminals into jail and imposing stiff penalties on those who break society's rules.

"From this point in human social development, it took just a tad more rejiggering of the same circuitry to bring our species to a mo­mentous place: We became disgusted by people who behaved immor­ally. This development, Curtis argues, is central to understanding how we became an extraordinarily social and cooperative species, capable of putting our minds together to solve problems, create new inventions, exploit natural resources with unprecedented efficiency, and ul­timately lay the foundations for civilization."



Kathleen McAuliffe


This Is Your Brain on Parasites: How Tiny Creatures Manipulate Our Behavior and Shape Society


First Mariner Books


Copyright 2016 by Kathleen McAuliffe


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