The Evolution of "Eww!"

Hygiene expert reveals the science behind disgust

Val Curtis photo.jpeg
Val Curtis, professor, London School of Hygiene and Tropical Diseases

Val Curtis believes disgust -- not love or any of the other "widely studied" emotions -- is the response that defines us as humans.

"Disgust has been a forgotten topic in psychology," Curtis said. "It's a great way of thinking about where we come from and why we do what we do. In short, it tells us what it means to be human."

A professor at the London School of Hygiene and Tropical Diseases, Curtis analyzed disgust as an evolutionary mechanism during a talk at Duke Wednesday called "Why Disgust Matters." The presentation, which elaborated on her new book "Don't Look, Don't Touch, Don't Eat," was part of the Duke Global Health Institute's (DGHI) Global Health Exchange series.

DGHI epidemiologist and event co-organizer Joe Egger said Curtis' research on hygiene brings many sides of the global health discipline together.

"Hygiene and pathogens are inextricably linked, and poor hygiene can lead to disease," Egger said. "An emotion as basic as disgust transcends global public health because if we can more fully understand what causes revulsion and disgust, we can understand how to develop hygiene interventions that tackle some of the world's leading killers, like diarrheal diseases."

Curtis began her presentation by removing "eww!"-inducing objects like fake feces, insects, chewed gum and hair from a bag and throwing them at audience members. Curtis was quick to remind the audience that although such encounters may be unpleasant, the response of revulsion was critical to our evolutionary ancestors' survival.

"Disgust is an adaptive system," Curtis said. "We evolved to keep away from pathogens and parasites so we could survive. Imagine if our ancestors had gone around eating (fecal matter) or touching disease-carrying animals. We wouldn't have been around long."

Because disgust is such a strong reaction, it is easy for policy makers to avoid talking about sanitation, said Curtis. As an example, she pointed to the ongoing lack of clean toilets in much of the world. She attributed this to the widespread taboo against talking openly about human waste. However, in Cambodia, a shocking national campaign depicting a man and a dog defecating openly prompted many citizens to install latrines.

"We need to talk about (feces)," Curtis said. "While disgust keeps us from getting sick, it also keeps us from talking about things we find disgusting. We don't talk about toilets, but they cause nearly 92 million deaths every year."

Curtis also discussed the moral dimensions of disgust, from humans' natural aversion to anti-social behaviors to disgust's role in xenophobic policies in much of the world until recent decades. She cautioned against relying solely on the "primitive" brain, which controls adaptive tools like disgust and fear, when evaluating a situation.

Chris Paul, a PhD. student in environmental policy, said Curtis got him thinking about connections between law-making and disgust reactions. As he moves forward with his research, he said he would more seriously evaluate the impact of basic emotions on policy decisions.

"She proved to us that the feelings are real," Paul said. "I found her discussion of the relationship of stigma and disgust particularly valuable. I realized these basic emotions have a powerful effect on which policies are put into effect. It's important to realize the motivations and consequences of feelings like disgust."