From IWU Magazine, Summer 2013 edition

That's Disgusting!

In examining what makes us feel revulsion, Daniel Kelly ’97
also reveals surprising truths about what makes us human.


“Minds and Morals” is among the courses Daniel Kelly ’97 (above) teaches at Purdue University.
Daniel Kelly '97

Humans know disgust when we experience it — the sense of revulsion after accidentally drinking spoiled milk or discovering the contents of the baby’s diaper on our hands.

But Daniel Kelly ’97 argues there is much more to disgust than a scrunched-up face and waves of nausea. He discusses the character and evolution of the emotion in his book Yuck! The Nature and Moral Significance of Disgust (MIT Press, 2011), taking the reader on a journey from understanding why humans naturally avoid rot and toxic foods to the question of why we avoid certain people.

Now an associate professor of philosophy at Purdue University, Kelly became interested in the topic, in part, after a conversation with his graduate advisor over a Chinatown meal of blood tofu and duck tongue soup. As his advisor savored the dishes, Kelly felt that familiar wave of nausea associated with disgust. He wondered why an emotion that seemed as primal could also vary so widely among individuals, so that a dish favored in one culture turned stomachs in another.

This and other questions involved in understanding “what makes people tick” is what got Kelly interested in philosophy to begin with. He majored in philosophy, along with English, at IWU and took his studies further with master’s and doctoral degrees in philosophy from Tufts and Rutgers universities, respectively.

As a graduate student, Kelly was intrigued by new research taking place in the area of moral psychology. “As I looked into that, I saw that some of the most interesting work was exploring the surprising link between disgust and moral violations, social transgressions — even value systems.”

Kelly decided to devote his dissertation to the subject of disgust, which eventually grew into his book Yuck! Since its publication two years ago (and released in paperback this spring), Yuck! has garnered rave reviews and turned the author into something of a worldwide authority on the subject. He’s been quoted on the disgusting aspect of topics ranging from Starbucks’ use of dye from crushed cochineal insects to color its Strawberries and Crème Frappuccino to the use of medicinal leeches and maggots in Indianapolis hospitals. (For the record, the pink dye in a strawberry frap doesn’t bother him. But don’t try to attach a leech to his leg.)

“I do worry that I’ve become The Disgusting Guy,” he playfully confided to Bloomington Pantagraph writer Dan Craft in an interview published in May. “It’s not all I do.” Kelly has published papers on such topics as moral judgment, social norms, racial cognition and cross-cultural diversity. As a member of Purdue’s faculty since 2007, he also teaches a range of subjects, including “Philosophy of Cognitive Science,” “Philosophy of Biology” and “Minds and Morals.”

Disgust, as it turns out, has surprising relevance to all of these areas and more. Especially intriguing to Kelly was how researchers across a range of academic disciplines and perspectives “were saying things about the emotion that were equally plausible, but that also looked incompatible with each other.” As a scholar who works “at the intersection of philosophy and the cognitive sciences,” Kelly set his goal to weave together all these different approaches “to better explain the operation and evolution” of a complex human emotion.

In his research, Kelly discovered that disgust — while “biologically attuned” to the muck and filth of the physical world — also exerts “powerful, almost subliminal influence over certain social and moral judgments.”

Exploring the unexpected links between disgust and mortality “was in my wheelhouse,” the philosopher explains. “Not just because it gave an intriguing window into human nature, but also because making sense of everything we were learning about disgust would, I saw, require a range of different theoretical tools.”

Hitting the road before buckling down

It’s the kind of interdisciplinary balance that Kelly first enjoyed as an IWU undergraduate.

“At Wesleyan you could engage in the frank discussion of ideas — and professors were very much a part of creating that environment,” he says. “It was a real joy to be able to argue with friends about things ranging from Hamlet’s soliloquies to scientific realism to the best Beatles album, and a lot of those conversations continue intermittently today.”

Kelly came to IWU intending to major in computer science, but took full advantage of its liberal arts curri-culum to explore other disciplines. An introductory philosophy course provided both a challenge and a comfort zone that led to his decision to major in the subject.

The idea of becoming a scholar didn’t hit him right away, however. Instead, his post-college plans were “entirely and weirdly Jack Kerouac-influenced,” says Kelly, referring to the Beat Generation icon whose On the Road documented the author’s travels across late-1940s America. Kelly devised his own plan “to hit the road and wander far afield — geographically, culturally, experientially — making sure I had an interesting biography by the time my number came up.”

After a year he hung up his backpack and applied to graduate school in philosophy at Tufts University in Boston. “I had been the kind of person who went to school for fun, and at Tufts I decided to buckle down and see how far I could take this thing.”

Kelly's book "Yuck!" won rave reviews and turned him into something of a worldwide authority on all things disgusting.
Yuck! The Nature and Moral Significance of Disgust

Kelly’s decision to pursue a path of scholarship was rewarded in the publication of Yuck! by MIT Press — considered one of the country’s top academic presses. Reviews were enthusiastically positive, including one from Cambridge philosophy professor Simon Blackburn, who wrote in the Times Higher Education: “I found it hard to put this book down, and recommend it as a shining example of genuine progress in moral philosophy, arising from bona fide increases in our understanding of who and what we are.”

Kelly begins his book by dissecting disgust at its most basic. Disgust is a reaction we first start to feel when we are 3 or 4 years old, triggered automatically by things like rotting food or visible cues of infection or illness.

The evolutionary advantage of physically recoiling from things that could make you ill is obvious. “Simply speaking, disgust is the response we have to things we find repulsive,” says Kelly. “Some of the things that trigger disgust are innate, like the smell of sewage on a hot summer day. No one has to teach you to feel disgusted by garbage, you just are.”

By fusing two previously distinct psychological mechanisms — one to protect us from consuming poisonous food and the other to guard against infectious disease — disgust became a uniquely human emotion, says Kelly. “Unlike similar emotions like anger and fear, which can be found in a range of other animals, I argue that only humans possess disgust.”

Kelly’s book has gotten special attention for its analysis of the link between disgust and morality. In Yuck!, he documents how this link was a result of humanity’s “gradual reliance on culture.”

“Mother Nature doesn’t start from scratch,” says Kelly. “She tinkers with what already exists. When people began to get more social and more reliant on cultural information, some problems came up. So Mother Nature did her tinkering thing and made disgust one of the mechanisms to help regulate social interactions.”

The dangers of disgust

Thus, from universal provocations of disgust like smelly garbage, humans began to use it as a social tool. “We continue to have this base layer of core disgusting things,” says Kelly, “and a lot of them don’t seem like they’re learned. But there’s also a whole set of things that have a lot of cultural and individual variation about whether it’s considered disgusting.

“The core base of what causes disgust has expanded to the point where certain kinds of moral violations, social transgressions, and even value systems of groups one is not a member of can come to be disgusting as well.”

Charles Darwin's 1872 book "The Expression of the Emotions in Man and Animals" used photos of psychiatric patients to illustrate disgust and other human emotions.
Charles Darwin image

In such cases, some ethicists have argued that disgust carries “an ancient wisdom” and is therefore “a trustworthy guide to justifiable moral judgments.”

Kelly believes the opposite: disgust’s role in morality should in fact be minimized by society, he says — in part because people tend to dehumanize what they find disgusting.

“The groups that are most likely to elicit disgust are often the lowest on the social hierarchy,” Kelly told the influential news website Salon. “Women have been made into objects of disgust a lot throughout history.” More recent examples include German Nazi propaganda that portrayed Jews in ways designed to evoke disgust.

“Disgust can be a very powerful rhetorical tool to discredit, undermine or demonize an opponent or a group of people with whom you don’t agree,” Kelly warns. “An easy way to do those things is to portray someone as infecting the integrity of your own social group. Disgust is a really potent emotion, and using it can be pretty rousing and effective because it has an almost subliminal influence on how we think of things.”

However powerful disgust may feel, “investing the emotion with moral authority is extremely dubious, and we shouldn’t uncritically trust it,” he continues. “We know the story of how it evolved and why it varies from one culture to the next. … A practice people are disgusted by may or may not be immoral, but the fact that people are disgusted by it is totally irrelevant to that particular question.”

Becoming more aware of the “dubious” connection between disgust and morality, Kelly now regards the emotion differently in his own daily life. “I’m much more aware of it in public spaces or casual conversations, which is what happens when you write a book and start noticing things with a hyperawareness of the word or the topic.”

His continuing research into the subject has even inspired Kelly to broaden his palate. Since writing Yuck!, he has “sampled delicacies around the world,” some that he might never have considered trying before. But there is one item that still makes his “skin crawl when I imagine putting it in my mouth.” Former classmates may want to take note, if they ever invite Kelly over for dinner: he’d rather pass on the jellied moose nose.

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