Would you drink juice in which a giant cockroach had just been swimming? Would you taste the milk from which a rat had just been removed? At the very thought of such a drink, did you withdraw your jaw in a reaction of disgust? Such feelings have accompanied humans for thousands of years, but they have not always signaled the same thing.

What makes us disgusted?

The characteristic grimace, nausea, and avoidance of the repulsive object is an innate reaction to the questionable taste of the food consumed. Meanwhile, people turn their faces not only at the taste but also at the idea of coming into contact with an unwanted substance. According to psychologist Professor Paul Rozin of the University of Pennsylvania, the conception of the disgust response is an evolutionarily acquired defense mechanism against expanding environmental contamination.

What makes us disgusted?  According to psychologist Professor Paul Rozin of the University of Pennsylvania, the conception of the disgust response is an evolutionarily acquired defense mechanism against expanding environmental contamination.

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Food for Thought: Paul Rozin's Research and Teaching at Penn

Rozin distinguishes what he calls the basic emotion of "core disgust" from the instinctual reflex of the distaste system. "Core disgust is qualitatively different, in terms of meaning, from distaste," he writes. "Disgusting items need not have negative sensory properties." The sense of disgust that overwhelms someone who bites into a wormy apple -- the feeling of revulsion, the spewing of chewed apple pieces, the approach to the brink of vomiting -- is not brought on because the worm tastes bad. The half worm is "found" by seeing it writhing in the bitten apple; it is not tasted at all. For Rozin and April Fallon, a graduate of Penn's Ph.D. program in psychology, this critical distinction implies that disgust is not merely an extension of distaste, but "an entirely new category of ideationally based, contamination-sensitive revulsion or withdrawal."

Most of the things that cause disgust -- food, feces, rotting flesh, and gore -- derive from animals. "Almost all disgusting food is of animal origin," Rozin notes. "There's all this animal food out there that's actually quite nutritious and rich, and people wouldn't be caught dead eating it." Most cultures eat only a very small and selective range of available animal foods. In American culture, we avoid virtually all invertebrates, reptiles, and amphibians, and eat only a few kinds of birds and mammals. Rozin recalls being struck by this "bizarre phenomenon" and being led into his research on disgust by an effort to understand it -- that and by his general love of and attention to food.

When I interviewed Paul Rozin in his office one afternoon, I found him at a desk submerged beneath a rising tide of books and papers. "I'm over committed," he told me as he leafed through papers and lifted books in search of a list of questions I'd faxed the day before. Still, he seemed to tread with ease the cross currents of research projects, administrative tasks, and teaching duties that surged about him. "I'm not very good at insulating myself from the ebb and flow," he confessed and then settled into a rust-colored reclining chair that boosted his white, sneaker-shod feet into the air. Although an answering machine held the ringing phone at bay and a screen saver of shifting geometric shapes hid his 50 daily e-mail messages, our brief interview session was continually interrupted. Rozin talked with his hands locked behind his head and his elbows splayed, pausing to lean forward and greet a graduate assistant passing through a nearby seminar room, to advise a harried undergraduate who'd forgotten the form he'd come to have signed, to issue collating instructions, or to deflect several other intrusions. "I'm doing an interview for the next hour," he'd call out cheerfully to someone appearing at the open door of the seminar room, and then return unperturbed to the course of his narrative while the phone rang.

Rozin has spent almost all of his postdoctoral years at Penn. He earned a Ph.D. in biology and psychology from Harvard in 1961. He emphasizes, however, that his formative academic experience took place in the curriculum developed by Robert Maynard Hutchins, the well known educator and president of the University of Chicago, where Rozin was an undergraduate from 1952 to '56. "To Hutchins," Rozin says, "a college degree represented a level of intellectual sophistication and understanding, not the number of years spent at a particular institution. His focus was on learning to think rather than on learning facts."

Rozin entered Chicago's undergraduate program at the age of 16, after only two years of high school. The University had advertised the availability of Pre-Induction Scholarships, which were funded by the Ford Foundation for high school students who could meet certain standards. Almost half of the entering class that year had no high school diploma, and some students were as young as 14.

Under Hutchins, the University of Chicago's curriculum was a writing-intensive program in which students read original sources, the "great books," and were taught by faculty in small classes; there were almost no textbooks or lectures. The undergraduate curriculum consisted of 14 one-year courses distributed across a variety of fields, with a written exam at the end of the year. If students could pass the exam without taking the course, they were released from the requirement. "Within two weeks of being there," Rozin effuses, "I realized it was the smartest intellectual decision I had ever made. My whole first two years of high school seemed trivial after just a few weeks in these wonderful courses. I got a real education."

In one of his publications, Rozin writes about how, through a process of internalization, values become a part of the self: "They are woven into the self," he writes. In his projects and priorities at Penn, it's not hard to discern the strands of Hutchins' influence woven into the fabric of Rozin's devotion to creating sophisticated thinkers. Musing on the decisive affect of his undergraduate experience at the University of Chicago, Rozin declared, "All this has been very formative in both my research and my teaching, so I value it enormously in my life. It's why I'm a strong proponent of general education -- because I saw how it opened my eyes."

Rozin teaches two introductory psychology courses every year: one a general honors seminar, the other a regular lecture course for 250 students. "He certainly has a passion for the subject," reports one of his students. "He conveys it to us every day; you do the work because you want to do it." His approach to teaching relies on the course textbook to convey the facts of the subject. "I'm more interested in the process of knowing," Rozin specifies, "the nature of science and scholarship, rather than the facts: How do we advance? What does it mean to find something out? How do we get evidence? How do we make that evidence into a theory?" To test students' mastery of these thinking skills, he gives only open-book exams that probe how students handle the course content.

In addition to chairing the first year of a committee that developed a numeracy and critical thinking component to Penn's curriculum, Rozin was twice director of the General Honors Program and the Benjamin Franklin Scholars Program (1974-1976 and 1988-1994). As part of Penn's honors program, high-achieving students participate in a variety of small and more advanced general education seminars. One of Rozin's innovations was to bring first class scholars to teach in the honors program: legal scholars, medical researchers, and even a psychologist-lawyer who taught a course on Buddhism and psychology. "It didn't matter what field they were in," he said. "They didn't even have to be in a straight academic field. I wanted students to see how you grapple with a problem from the ground up."

Rozin cites the recruitment of Penn alum and author Chaim Potok as his crowning achievement as director of the honors program. Initially, he tried to get Potok to teach a course on modern intellectual history, but since Potok was at work on a nonfiction book, he was reluctant to invest the preparation time. Rozin picks up the story: "So I said, 'Why don't you just do a course on this book and teach the class how you assemble someone's life?' And he said, 'I could do that in a course?' And I said, 'Sure, that'd be great for the students; they'd get to see how a scholar puts together people's lives.'"

Potok expressed concern that many of the documents he was reviewing in his research were in the original languages. "So I said, 'I will get you a native speaker of Russian, a native speaker of Chinese, and a native speaker of Hebrew.' And he said, 'You can do that?' And I said, 'No problem, we have loads of international students in the honors program.'" After the students had spent a semester studying Potok's research methods and his chronicle's subject, Rozin arranged to have the book's central figure, Volodya Slepak, flown in from Israel so that the class could meet and interact with him. In The Gates of November , Potok acknowledges "the keen minds and respectful interest" of the students in the 1992 Benjamin Franklin Honors Seminar.

"Teaching is important in my life and in my contribution to Penn," he confides. "Nothing gives me a bigger charge than when one of my undergraduates comes back and says one of my courses made a big difference to them." The most cherished honor of Rozin's career is the Ira Abrams Teaching Award, which was bestowed on him by the School of Arts and Sciences in 1995. He is also the first recipient of the Edmund J. and Louise W. Kahn Professorship for Faculty Excellence, a chair he will hold until 2002. The chair supports a Penn professor in the School of Arts and Sciences with a distinguished scholarly record, one who displays excellence in teaching and research, and who is an innovator in curriculum development and student service. The Kahn Chair carries a modest research fund that Rozin appreciates because, as he points out, "I open up fields rather than mine them -- the research support community likes to support people whose work falls within clearly established paradigms."

Rozin's interests have been shifting in recent years to how cultures alter human nature in fundamental ways. "I've gone from being, when I first came to Penn, an animal psychologist interested in the brain's physiology and evolution to being more like an anthropologist studying culture as it impacts on somebody."

Not long ago, he went to live and work in India for a month. "One of the first things I realized is how different Hindu Indians are from Americans," he relates. "I was astounded, and I said to myself, 'If academic psychology had started in India, it would look so different from what it does now.'" He describes Indian culture as a communal culture where concepts like purity are central to life, where food is a quintessentially moral substance, where you don't choose your spouse or your career; it is a much more traditionally determined rather than an individual-choice determined culture. "Our view that pleasure is a basic principle of life is seen as a crazy idea," he exclaims. "We're at a very striking historical point where individual choice has been put on a pedestal -- this idea that, if you just optimize for yourself, it's gonna be a great world is a peculiar and atypical view." As Rozin describes it, the Indian counterpoint is that the good life is basically the living of a proper life, which is prescribed by tradition: to have a family, and to treat your family and your gods appropriately.

"I've really been captivated by the Indian world -- just how different it is -- and what a different starting point it might be for trying to understand the human mind," he avers. "A lot of my work in the future is going to be oriented that way: I just want to see if I can bring this to the attention of psychology and show how some of our basic assumptions might be questioned."

A former department chair (1978-1981), Rozin asserts that an important characteristic of Penn's highly ranked psychology department that has contributed to its distinction is what he calls its "good taste." The department fosters good taste by seeking and encouraging faculty who are not captured by intellectual fads but who have a more flexible and broader perspective in relation to the discipline. Rozin notes that the department has recently hired a faculty member who fits his good-taste profile. Steve Heine is fluent in the Japanese language and knows that culture well; his field is Japanese self-esteem. Rozin also points to his own participation in the establishment of an institute at Penn to study ethno-political warfare. The initiative is being sponsored by the American and Canadian psychological associations and will have sites in places like Bosnia, Sri Lanka, and Algeria where postdoctoral fellows can acquire firsthand experience of the subject matter. The purpose of the multisite institute will be to understand the processes that lead to this type of violence and to study how it can be ameliorated. Because psychology in academic institutions tends to associate most closely with the natural sciences, Rozin believes there are many scholarly benefits to be reaped by a broader cross-disciplinary exposure. "Psychology has much to learn from disciplines that study larger phenomena," he asserts. "I think this is going to be a great vehicle to connect psychology with other social sciences -- it's a good idea for the whole discipline and for psychology at Penn."

Rozin now has research connections and opportunities in India, Japan, and France that nourish his growing interest in cultural comparisons as a way to illuminate basic human nature. One area of research connecting this new interest with his long-standing interest in food is a data gathering effort comparing how food functions in American and French life. With his French colleague, Claude Fischler, Rozin claims that the French have a better and more sensible attitude toward food: they enjoy it more and eat better tasting food. Americans, particularly women, think of food -- "one of the great pleasures of life" -- as an ambivalent thing. If you ask French and American subjects whether, when they think of fried eggs, do they think of breakfast or cholesterol, the French are more likely to respond in terms of the former and Americans in terms of the latter. In one case, it's a supposedly harmful nutrient, in the other it's a culinary context. "We tend to think about what's in the food that's either good or bad for us," explains Rozin, "and the French think about it as an experience: it's eating. They're thinking about it in the mouth, and we're thinking about it in the bloodstream."

In examining how the French and Americans have come to think in these divergent ways, Rozin has also begun to study how American attitudes toward food are shaped -- malformed to be more precise -- by information conveyed through the media from the scientific and health communities. "People do not understand some of the fundamental issues of nutrition and science," he argues. In Rozin's view, Americans' overemphasis on diet and health tends to make eating into an unpleasant experience. Even the educated public commonly misconstrues the import of scientific findings, believing that the results of a particular study represent the establishment of "fact" or knowledge. His own surveys have shown that a substantial minority of Americans hold the extreme belief that salt and fat are toxins, a misperception exploited to sell foods marketed as sodium- or fat-free.

In America, eating fat has almost become immoral, and many people report being disgusted by obese people. "I've gotten on a little bit of a quasi-preaching mode," he chuckles. "I see myself opposed to what I call the nutrition police in this country who tell you what you should and should not eat." In his research on disgust, Rozin has pointed to how a culture's moral system recruits disgust and projects the emotion onto what is considered immoral. It's a two-way process: disgusting things are more likely to be thought immoral, and immoral things are more likely to be thought disgusting. In America, the process can be readily observed in how cigarette smoke and ashes have become offensive. Except for advertisements, cigarettes were hardly even a topic of public comment 20 years ago; now clusters of ostracized smokers huddle on the sidewalks outside office buildings -- even in winter.

In the early stages of its cultural evolution, the food focus of disgust remains but rejection shifts to the idea of what the food is: it is an animal product. Although the disgust emotion has been disconnected from taste and derives from the meaning rather than the taste of food, the rejection reflex still "accesses" the basic distaste system of facial expressions, nausea, withdrawal, and revulsion. This process of "preadaptation" -- where a system, process, or structure evolved for one function is "accessed" and used for another -- marks both a boundary separating and a continuum connecting our composite human-animal nature.

Together with Jon Haidt and Clark McCauley, also graduates from Penn's doctoral program in psychology, Rozin conducted surveys asking North American respondents to list the things they considered disgusting. The final tally included examples from the core disgust domain as well as examples of inappropriate sex, deficient hygiene practices, death, and "violations of the body envelope" or gore and deformity. This set of disgust elicitors makes up the wider category of "animal-nature disgust," the withdrawal from things reminding us that we are fundamentally biological creatures. "Anything that reminds us that we are animals elicits disgust," Rozin writes. "Disgust functions like a defense mechanism, to keep human animalness out of awareness." An analysis of a "disgust-sensitivity scale" developed by Haidt, McCauley, and Rozin indicates that death is the chief elicitor of disgust. This finding led Rozin and his research associates to conclude that "the most threatening aspect of humans' animalness is their mortality, and that disgust serves as a defense against pondering mortality." Human consciousness, as it were, accesses the pre-existing distaste system, and all its involuntary mechanisms of revulsion physically force us to avoid contemplating our undeniable predicament: we are animals that must die.

With the implication of disgust in morality, the emotion loses both its original connections to bad-tasting food and its intermediate function of avoiding reminders of animal nature and death. At this level, disgust expands to a general system for putting out of mind, like smokers cast out of the office, anything one's culture considers offensive. Disgust then becomes a powerful form of negative socialization and an abstract moral emotion. "In my work on the evolution of disgust," offers Rozin, "part of my interest has to do with setting up a model of how a piece of biology can become transformed by culture; part of my goal is to say, 'here is a way we can see how some of our biology maps into cultural systems.'"

Rozin's analysis suggests a cultural evolution of disgust that, in his words, "brings it to the heart of what it means to be human." He elaborates: "It's hard to imagine civilization and culture without disgust, the sense of what's inappropriate. If you could imagine a person who is free of disgust, it's sort of hard to imagine how they would be distinctly human. It's got to do with the modern sensibility; it is the -- the -- sign of civilization."

Together with David Kritchevsky, a biochemistry professor at Penn's Wistar Institute, Rozin has taught a general honors course called Diet and Health. In the class, students explore the complex mix of scientific method, politics, and personal issues that go into the formation of a scientific consensus over matters of healthy food. "There's a lot of interesting politics involved," he observes. When seeking the backing of the scientific establishment or the government, researchers invest considerable energy and reputation in their work and have a propensity to turn results from a few studies into a single, clear-cut directive for health and eating. So much so that, once the medical community recognizes publicly that high cholesterol, for instance, is generally unhealthy -- which is true -- it becomes difficult to publish findings on research showing that there are benefits to cholesterol or that for many people high cholesterol is not a risk factor. "This is nothing special," Rozin cautions, "this is the nature of political entities, but it includes medical science. As a sophisticated citizen, you should be able to read the New York Times and not just understand it, but understand what the basis for the story is: what might be conjecture, what kind of things you would want to know in order to be sure that what you're reading is what really happened or what was really found."

Such talk of broad, nuanced, and sophisticated thinking sounds a lot like Robert Hutchins' educational agenda woven into Paul Rozin's special sense of "good taste." Linking his roles as researcher and educator, Rozin is in the midst of writing, with Professor Kritchevsky, a book for the general public that discusses how to think sensibly about food. "I want people to respect science as the best show in town for establishing truth, for establishing knowledge -- but as one that is imperfect and takes a while to get everything right. I don't want people either to think it's worthless or that it's perfect. And that's very hard to do."

Paul Rozin's Research and Teaching at Pennsylvania University about disgustion reasons

What makes us disgusted?

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