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Pychologist Paul Rozin, AB'56, studies what humans eat--and what divides yum from yuck.
By Peter Nichols / Photography by Dan Dry

At one of their weekly lunchtime seminars, faculty of the University of Pennsylvania’s Solomon Asch Center for the Study of Ethnopolitical Conflict gathered this fall to hear Paul Rozin’s talk on “Negativity Dominance.” Rozin, a psychology professor at Penn and one of the center’s founders and co-directors, had arranged for the delivery of some of his favorite dishes from an Italian deli near his home in suburban Philadelphia. A paper plate heaped with breads, meats, pastries, and pickled stuffed peppers sat on the table before him.

“Negative events have this powerful, almost uncancelable quality,” he began. In the wild, bad experiences usually result in death and are therefore potent teachers for animals. Negative risks outweigh possible positive outcomes: There is nothing as positive as death is negative. Humans too, Rozin told the dozen or so scholars gathered around the table, are programmed to respond promptly and strongly to negative experiences. A cockroach in a glass of orange juice, for instance, elicits a nearly insurmountable sense of disgust, and people cannot be persuaded to drink it even if they have been assured the bug was sterilized. There is nothing positive that can be placed on a pile of cockroaches to make them edible. “Similarly,” he reasoned, finding an analogy between such disgust and long-standing ethnic hatreds, “if someone murdered your great-great-great-grandfather hundreds of years ago, it seems there’s nothing you can do to get away from that. There’s no counter-cockroach!”

As the conversation continued, Rozin, AB’56, took hearty mouthfuls of Italian delicacies, returning to fill his plate several times at the small buffet. It was hard to tell whether his unself-conscious pleasure derived more from the luncheon fare that he had supplied or the food for thought, which he also provided.

The author of nearly 200 scholarly articles, Rozin is an authority on the psychology of food choice. Twice elected a fellow of Stanford’s Center of Advanced Study in the Behavioral Sciences, he has also been editor of Appetite and served on the editorial board of the Journal of Gastronomy, as well as the advisory board of the Children’s Television Workshop, which produces Sesame Street. He is currently psychology adviser for the publisher W. W. Norton, and his expert advice has been tapped by major food producers like Unilever, Nestle’s, General Foods, McCormick Spices, and Cadbury-Schweppes.

Although a joint Ph.D. in psychology and biology from Harvard prepared him mainly for biological psychology and animal research, Rozin is an intellectual omnivore. In his 36 years at Penn, he has investigated how humans come to develop food preferences and aversions, studying the interplay of culture and cuisine, morality and disgust. To understand what makes people like or dislike certain foods, Rozin has sunk his teeth into fields as diverse as anthropology, economics, geography, history, marketing, medicine, psychology, sociology, and public policy.

He attributes his wide-ranging interests to his experience in the College, where he matriculated at the age of 16 after two years of high school. “We dug into a lot of different disciplines in some detail,” he remarks. “I’m not saying my broad research style is good or bad, but it’s the way I work. I just get interested in a problem, and I go where it seems right to go.”

Despite the sensual and intellectual pleasure he derives from food, Rozin is trim. He possesses what he calls a “rather small” collection of about 200 cookbooks on world cuisines, particularly Asian, and sometimes leafs through them for inspiration in cooking an occasional meal. “But I’m too busy to cook now,” he confides. “I hardly have time to eat.” He dines out frequently, particularly as he travels around the world for conferences and consulting. A self-described neophile, he enjoys sampling unusual foods and flavors, including Japanese candied locusts and a dish made of ground, dried, cactus worms. “I love to eat all kinds of exotic foods and cuisines,” he says, “and have eaten well nigh everything cooked—almost.” One often-reviled food that he hasn’t eaten is haggis, a Scottish dish consisting of a sheep’s heart, liver, and lungs, minced with suet and oatmeal, and boiled in a pouch made from a sheep’s stomach. The reason, he claims, is not disgust but lack of opportunity.

For humans, whether doing a power lunch, enjoying a romantic candlelight dinner, or eating the apple from the Tree of Knowledge of Good and Evil, food and its consumption are freighted with significance beyond nutrition. To extract the mix of biological, psychological, and cultural ingredients that go into people’s daily decisions about what foods they eat, Rozin has studied a range of foods in a range of ways. He’s looked at the generational link in how some cultures acquire and pass on to their children a preference for initially unpleasant eating experiences, such as the burn of chili peppers. (In a “hedonic reversal,” he explains, the fierce burn becomes a sought-after culinary experience.) He’s found that the sensory experience of chocolate—its rich aroma, its silky and slippery sweetness—is what underlies people’s chocolate cravings, not the mildly addictive qualities of some of its ingredients. Chocolate, he exults, “is a wonderful thing in the mouth.”

With David Kritchevsky, SB’39, SM’42, a professor at Penn’s Wistar Institute and an expert in the biochemistry of nutrition and fat metabolism, Rozin is writing a book to help readers think sensibly about food and nutrition—and to enjoy eating. The book is an outgrowth of a course that the two men taught at Penn. In Diet and Health, students explored the complex mix of scientific method, politics, and personal issues that help form scientific consensus over what constitutes the “healthy” diet. For many Americans, Rozin believes, the concept of a diet filled with healthy foods has had a pernicious effect.

“One way Americans have spoiled eating,” he says indignantly, “is by thinking of their blood cholesterol while they’re doing it—which is nuts! Every bite, for some people, is fraught with conflict. It may be that we’re obsessed by death. There’s this sense that we’ll live forever, if we only do it right—and diet, along with exercise, is currently thought to be the way to do it right.”

Experimental results about the health effects of eating particular foods get reported almost immediately, but Rozin argues that, in many cases, the public has not learned to evaluate such information in a way that balances risks and benefits. Instead, he says, many people have adopted simplistic decision-making criteria to help form judgments about whether particular foods are either good or bad. Under this heuristic, for example, essential nutrients like salt and fat may come to be viewed as poisons. Yet, he points out, “driving is far more dangerous than high cholesterol. If people cut driving in half and walked more, it would probably do much more for their health than monitoring their diet on a moment-to-moment basis.”

According to Rozin, the U.S. medical establishment’s preoccupation with what foods constitute a healthy diet also has added to American women’s “normative discontent” about weight and body image. He cites his recent survey of college students from six campuses across the U.S. In that study, more than 10 percent of the female respondents admitted that they are “embarrassed” to be seen buying a chocolate bar, while 30 percent said they would be willing to take a nutrition pill—and forgo eating. “About one quarter of Americans, mostly women,” Rozin adds, “if asked for the first few words that come to mind when they think of chocolate, mention both a positive and a negative word: ‘delicious’ and ‘fat.’ They’ve taken this incredibly delicious food, and they’ve made it into something like a toxin.”

This uniquely American food-poison attitude has inspired the food industry to develop all kinds of popular products modified to be “healthier.” The highly processed, fat-free, low-salt, no-additives cuisine reduces the pleasure of eating and increases the cost of food, Rozin says. “I’m particularly interested in this pleasure issue—in being able to enjoy the wonderful things in life.”

With a French colleague, Claude Fischler, he spent last summer in Dijon at the Centre European des Sciences du Gout, gathering data for a comparison of how food functions in American and French life. He hopes it will become a major study: “I think we have something to learn from the French.”

If you ask French and American subjects whether fried eggs make them think of breakfast or cholesterol, Rozin says, the French are more likely to respond in terms of the former and Americans in terms of the latter. In one case, it’s in a culinary context; in the other, it’s a supposedly harmful nutrient. “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.”

Ironically, recent studies show that life expectancy is about the same in France and the U.S. The French eat a higher-fat diet, have higher levels of blood cholesterol, and do not worry about a healthy diet, yet still have a rate of cardiovascular disease that is about one-third less than Americans. “The trade-off between the pleasure of eating and long-term health,” Rozin says, “is not nearly as stark as Americans make it out to be.”

Attempts have been made to explain this so-called French Paradox in terms of what the French eat, the most popular account being the protective effect of consuming red wine. Other explanations are seldom considered: The French consume fewer calories, snack less, and eat a more varied diet at a slower pace. Their lifestyle is less stressful, especially with respect to food, and they probably exercise more, depending less on cars and more on walking and bicycling. “It’s not a paradox at all,” Rozin declares. “It’s only a paradox if you believe that saturated fat is basically the determinant of heart disease—as opposed to a causal contributor.”

From studying how humans come to divide foods into “the yum and the yuck,” Rozin has moved over the years to a focus on the “yuck,” the peculiar nature of human disgust. “Once I became interested in food and why people like it,” he explains, “it didn’t take long to realize that the strongest response people have to food is disgust.” Siding with Darwin, he traces disgust back to “a basic biological motivational system,” a response the father of evolution associated with the sense of taste.

Observed in a number of animals, in humans the characteristic yuck response is a gape that consists of opening the mouth and putting out the tongue. Often including nose wrinkling and raising the upper lip, this facial contortion allows the offending food to drop out of the mouth and is usually associated with a sense of revulsion, even nausea. The reflex, which serves as a potent survival instinct against toxic substances, is particularly vital to omnivores like humans, who experiment with all kinds of potential foods.

Rozin distinguishes this instinctual reflex from what he calls “core disgust”—a uniquely human response to the meaning of a revolting substance rather than to its taste. “Humans see themselves as quite distinct from (and superior to) other animals,” he writes in a chapter on disgust in the Lewis and Haviland’s Handbook of Emotions (1993), “and wish to avoid any ambiguity about their status by accentuating the human-animal boundary.” Although humans have developed language and culture and conceive of themselves as moral beings, they still eat, excrete, and copulate like other animals—and are profoundly ambivalent about this aspect of their nature and what it portends. “Disgust,” he notes, “functions like a defense mechanism to keep human animal-ness out of awareness.”

At the heart of Rozin’s theory of disgust is the contagion principle, which represents a kind of thinking that anthropologists call “sympathetic magic.” The law of contagion states that when two entities—such as eater and eaten—make physical contact, a permanent transfer of properties takes place from one to the other. In a 1990 experiment, Rozin tested people’s implicit belief in the adage “you are what you eat” by giving several hundred American college students one of two versions of a short vignette describing the “Chandorans,” an imaginary tribal society that hunts marine turtles and wild boars. Half the group read that the Chandorans ate wild boar and hunted turtles for their shells; the others read that the tribe ate turtles and hunted boars for their tusks.

The students were then asked to rate members of the culture for personality traits and physical attributes that could be associated with boarness (aggressive and likely to have beards, for instance) and turtleness (good swimmers). Those who read that the Chandorans ate boar rated them high on the aggressive scale, while those who thought of the Chandorans as turtle-eaters rated them good swimmers. “We know ‘you are what you eat’ is false,” explains Rozin, but despite sophisticated rational and conceptual faculties that tell us otherwise, “it nonetheless creeps into our judgment.”

The contagion principle, he says, comes into play with many living things, like a cockroach or a worm, that people find disgusting but that don’t really taste bad. Even the meats humans do eat, such as cows, pigs, and sheep, are rendered more palatable by disassociating them from their animal origin: rather than eat dead animals, we dine on “beef,” “pork,” and “mutton.”

In a 1993 survey, Rozin and his colleagues (he most often works with a colleague at Bryn Mawr College and three of his former doctoral students at Penn) distributed a questionnaire to gauge respondents’ sensitivity to a list of disgust elicitors that included food and eating, feces, rotting flesh, gore, deformity, deficient hygiene practices, inappropriate sex, and death. On the resulting Disgust Scale, death—whether an actual corpse or the odor of decay—is a primary elicitor. At the root of awareness, Rozin argues, humans believe they will be infected by contact with things that remind them of their animal nature, with death the most threatening attribute of animal nature.

Rozin and his colleagues theorize that the emotion of disgust appropriates the behaviors and sensations of the distaste reflex through “preadaptation,” a process in which an organism employs a physiological mechanism that evolved for a particular function to serve an entirely different purpose. Just as language articulation uses the mouth, tongue, teeth, and lips—all of which originally evolved for eating—human consciousness, argues Rozin, accesses the pre-existing distaste system. So obvious and painful—in short, so repulsive—is the prospect of mortality that human consciousness must enlist its animal reflexes to push it away. “Disgust evolves culturally,” writes Rozin, “and develops from a system to protect the body from harm to a system to protect the soul from harm.”

As the emotion of disgust is elaborated culturally, it evolves into a more general feeling of revulsion, a moral emotion associated with anger and contempt. In a kind of cultural preadaptation, Rozin theorizes, the biology of disgust is accessed in the formation of social mores. He calls the process “moralization,” in which a culture’s moral system recruits disgust and projects the emotion onto what is considered immoral.
For example, eating high-fat and “junk” food has come to be seen as immoral in certain sectors of American society. In a 1995 experiment, researchers at Arizona State University offered college students contrasting vignettes of students who dined on fast foods and others who ate a healthy diet. When asked to rate the two types of eaters, the “you are what you eat” principle again came into play, with respondents rating the junk-food eaters less morally worthy and less considerate than the students described as eating fruits and vegetables.

Researchers have found that vegetarians who abstain from meat based on moral principles (because it implies killing animals or wasting resources) are more likely to experience a linkage between values and food preferences. Rozin—who describes himself as a “moral vegetarian sympathizer”—has found that such vegetarians often come to dislike or be disgusted by meat, confirming a general rule of moralization: disgusting things are more likely to be thought immoral, and immoral things are more likely to be thought disgusting. When this stage is attained, the moral principle has become internalized or “woven into the self.”

As moralization of some entity or behavior takes hold in a society, a widening consensus builds and the forces of government and major institutions become aligned against what has come to be seen as repulsive. Take smoking: Today in the U.S., cigarette advertising has been severely restricted, tobacco companies and their executives have been vilified in the media, and legislation has curtailed smoking in public spaces.

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, says Rozin, disgust expands to a general system for putting out of mind—like the clusters of ostracized smokers huddling on sidewalks outside office buildings—anything one’s culture considers offensive.

“Disgust becomes, in many ways, the emotion of civilization, in the sense that much of the civilizing process involves developing distinctions between animals and humans, and a special sensitivity,” says Rozin, traveling far beyond the study of food likes and dislikes to the essence of humanity. “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 hard to imagine how they would be distinctly human.”
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