Mystery of Disgust
Why do we love eating lobster but recoil at the thought of boiled roach? Erik D'Amato examines the surprising reasons we find certain things gross.
By Erik D'Amato published January 1, 1998 - last reviewed on June 9, 2016
A well-heeled and well-respected investment banker in his late 50s made a small and decidedly unfortunate media splash in October 1995. Gerard Finneran, returning to the United States on an international flight and incensed when he was denied a drink for acting intoxicated, allegedly went on a rampage in the airplane's cabin, terrorizing the crew and passengers before being arrested when the plane touched down in New York. While the most serious charge facing the executive involved physically assaulting a flight attendant, what breathed life into the story was the airline's astonishing charge that, in the middle of his tantrum, Finneran scaled the beverage cart he was demanding access to, pulled his pants down, and defecated on it. According to the airline, Finneran used linen napkins as toilet paper, wiped his soiled hands on various surfaces, and then, charged the criminal complaint, "tracked feces throughout the aircraft."
News of what one tabloid newspaper called the "Jet-Mess Exec" instantly made its way around Wall Street, and reaction there was swift and harsh. Clearly, what Finneran had done was unspeakably disgusting–so disgusting, in fact, that some suggested only half jokingly that he would have been better off committing suicide on the spot. Long after the results of his spectacular indiscretion had been scrubbed away and deodorized, the stain on his reputation would linger. In all likelihood, his career would be finished and his life never the same.
While this disturbing tale certainly says something about the unfortunate Mr. Finneran, it says something equally important about his fellow passengers, the newspaper editors who rushed the story to press, and everyone who has since heard about the incident. What it says is that the emotion we call disgust–our feelings of repulsion toward certain objects, behaviors, and people–is tremendously powerful. What it doesn't say is that disgust is also one of only a handful of uniquely human emotions, one that speaks to both our deepest, most irrepressible instincts and to our penchant for taming these instincts.
THE ORIGINS OF DISGUST
Charles Darwin, in his classic book, The Expression of Emotions in Man and Animals, took perhaps the earliest scientific look at disgust. Recalling a colorful incident from an expedition to South America, Darwin wrote: "In Tierra del Fuego a native touched with his fingers some cold preserved meat which I was eating at our bivouac and plainly showed utter disgust at its softness; whilst I felt utter disgust at my food being touched by a naked savage, though his hands did not appear dirty."
By putting his finger on the meat, the Indian helped Darwin put his finger on three key aspects of disgust: first, that it can be elicited by quite different things–in this case, food and people; second, it is an emotion shared by radically diverse cultures; and third, what different cultures consider gross can vary tremendously. Darwin then inventoried the physiological reactions to disgusting things. At one end of the scale is a frown, often accompanied by hand gestures or body language aimed at pushing away or shielding against the repulsive object. In more pronounced cases, a person's mouth may drop open, and he's likely to spit, purse his lips or blow air out between them, and make an "ach" or "ugh" sound. Episodes of "extreme disgust," Darwin observed, tend to produce facial contortions identical to those observed before vomiting–mouth wide open, nose wrinkled, upper lip retracted and lower lip protruded–and some actually do double over and retch.
As for the larger question of why humans feel disgust, the great pioneer was silent, and for almost a century the scientific explanation of disgust approximated a Supreme Court Justice's famous take on the equally dicey question of pornography: "I can't define it, but I know it when I see it."
NUMBER TWO AS ENEMY NUMBER ONE
And we all do know it when we see it–or at least when we smell it.
What is the most disgusting thing you can think of? Perhaps it is the "gift" the rampaging banker left on the plane. Maybe it's a broken fridge full of rancid meat, a cave teeming with slugs and maggots, or a busload of unbathed hermits with beastly body odor and oozing pustules.
It's no surprise if you're grossed out by these images: the predictability of your response at least partly explains why so little follow-up was done with Darwin's work. In the logic of evolution, humans, quite simply, should have no interest in ingesting or being near things that–like excrement or rotting carcasses–are liable to infect or otherwise harm us. Disgust, from this standpoint, seems like an open-and-shut case of survival by aversion: we develop a primal response to harmful things that is so strong, and so automatic, that even the most spectacularly slow-witted among us are smart enough to walk the other way. It is, after all, one of the few emotions that is almost totally explicit; unlike someone who feels sad, for example, a person seldom walks around wondering what has made them feel so disgusted.
Had Darwin spent as much time in a nursery as he had in the field, the study of disgust might have taken a much different turn. The key problem, as Freud and others later observed, is that humans don't really exhibit aversions towards most of what we consider disgusting–including our own excrement–until we are taught to. Even worse, those famous feral "wild children" plucked from the forests were often almost totally lacking a "nominal" capacity for disgust. Finally, our closest primate cousins, such as chimpanzees, fail to exhibit disgust of any kind, and many mammals routinely ingest feces to replenish the beneficial bacteria that they, like we, carry in their digestive tracts.
On closer examination, then, disgust appears to be a cultural acquisition: people are taught what is disgusting, when to be disgusted, and, if all goes right, how to avoid being disgusting themselves. Indeed, "disgust marks the boundaries of culture and boundaries of the self," University of Michigan law professor William Ian Miller noted in his recent book, The Anatomy of Disgust.
But is there more to the story?
Plunging head first into this and other murky questions about disgust is a small number of dedicated (and strong-stomached) researchers. Their undisputed leader: Paul Rozin. Ph.D.. a professor of psychology at the University of Pennsylvania who has earned the label "Dr. Disgust" as a result of his untiring exploration of what grosses us out.
To the fundamental question of "nature versus nurture," Rozin's answer is blunt: "It's both." The "gape," one of the facial expressions Darwin described, is, he explains, indeed quite primal. "It derives from the 'distaste face,' which humans share with rats. But it has now gone way beyond that."
Like rat pups, newborn humans will involuntarily reject certain tastes. At birth, this sense of distaste is centered not on excrement but on foods that are bitter or sour or are, like chili peppers, irritating or painful.
What happens next is hazy. According to Rozin, at some point between ages four and eight we develop an acquired sense of disgust that is different from this innate sense of distaste. Just as we learn to like some tastes that we earlier rejected, like spicy foods, we learn to hate things we might have previously been interested in–most importantly, what we have been taught to flush and never discuss at the dinner table.
ARSENIC AND OLD WASTE
How does this new disgust response differ from the earlier rejection based on taste? Imagine three glasses of tap water. You are told that the water in the first glass contains an odorless, harmless chemical that is terribly bitter to the taste. The second glass is laced with a lethal dose of arsenic. The third glass, perfectly sterile and containing pure water, previously held a sample of dog feces but had been washed thoroughly.
Which glass would you drink?
This taste test, similar to an actual trial used by Rozin, suggests that disgust is about something much bigger than unpleasant tastes, smells, or sights. "Disgust," explains Rozin, "involves rejection based not on sensory properties, but on knowledge of the nature of something." And it is not necessarily about fear of injury or sickness. Knowing about the poison in the second glass incites a different, less violent reaction than knowing what used to be in the third. In fact, the difference between simple fear and disgust is as startling as it is stark: roughly speaking, if fear is our response to real or perceived harm to our physical selves, disgust is, in a sense, the reaction to actual or imagined threats to our souls.
ALL DISGUSTS GREAT AND SMALL
A good deal of research has involved the search for what experts call "core disgust." There is now general agreement that a "core" group of disgusts does exist, and Rozin and April Fallon, Ph.D., have identified three criteria that separate such "core" disgusts from things that are disgusting in some less profound way. To gain membership in the core disgust club, the candidate must be all of the following: something you could eat; something that has or had a life of its own; and something that has the power to make other things disgusting.
IT'S IN YOUR FACE. Freud saw disgust as an artificial response designed to tame children's sexuality. But he was, in this case, way off. In the 1940s, psychotherapist Andras Angyal argued that the mouth is crucial to disgust, and subsequent researchers have concluded that it is mainly an oral defense. "Disgust starts with food," says Jonathan Haidt, Ph.D., once a student of Rozin's and now an assistant professor of psychology at the University of Virginia, "and then moves on to other things, sex being just one of them."
IT'S ALIVE. Rozin and Fallon note that disgusting things are most likely to be, or are perceived to be, of animal origin, whether it's an actual critter or one of its body products. Also high in offensiveness are animals that eat other animals, wastes or decaying food, and animals like spiders and sea creatures that seem bizarre and alien.
AND IT'S SPREADING. Rozin and his colleagues contend that a central property of core disgust is that the object deemed offensive is capable of "contaminating" other objects–even if the person sensing this contamination knows that it's just an illusion. For example, while you might hate carrots with a burning passion, you are unlikely to reject a bowl of mashed potatoes because a carrot stick had fallen into it and been fished out. But what about a bowl of potatoes touched momentarily by an ugly but thoroughly sterilized cockroach? And what if the bowl of roach-"contaminated" potatoes is added to a larger bowl of potatoes? If the law "once in contact, always in contact" applies, a core disgust has likely been triggered.
Working with the foundation of core disgust, Rozin, Haidt, and Clark McCauley, Ph.D., have sought to isolate different kinds of disgust, to create a "pantheon" of other disgusting things, people, and practices, and to create useful tests (See "How Much Can You Stomach?" page 42) to measure a person's disgust sensitivity. To do this, they've broken down disgust into several distinct categories: foods or potential foods; body products; certain animals; death (e.g. contact with corpses); poor hygiene; certain sexual practices; "violations of the exterior `envelope' of the human body" (such as amputations or over-the-top body piercings); and certain moral offenses or offensive people.
LOVE IS THE ANSWER
The vagueness of what people find sexually disgusting was illustrated in an episode of the popular TV sitcom Friends, when one of the show's twenty-something bachelorettes discovered that, to her horror, the mature-looking beau whom she had just had sex with was, in fact, not even old enough to vote. Why, why, why, the spurned teen wanted to know, was Monica suddenly rejecting him? "Because," she stammered, "it's icky."
Monica's eloquent explanation notwithstanding, the fact is that sex itself–all sex–is potentially disgusting. After all, just making out usually involves exchanging gobs of spit with someone else. When we have sex, Rozin notes, we temporarily "suspend" our capacity for disgust, something most of us will do only under certain circumstances. "Except for very promiscuous males who will stick their tongues in the mouths of virtually any woman," he says, "imagined sexual encounters with most other people are usually considered offensive." We're talking about realistically imagined scenarios with ordinary people here, not fantasies of sanitized sex with airbrushed supermodels. And sex gets really disgusting when it is judged deviant–when, as in Monica's case, one partner is extremely young or old or, in rare cases, isn't even human.
Which brings up an even murkier issue.
We've all called someone "disgusting" for doing something brutish or insensitive–for example, when we call an ambulance-chasing lawyer "disgusting." It's tempting to dismiss this as an altogether different phenomenon from "normal" disgust. But intriguingly, in most cultures the same word used to describe feces and decay is also applied to morally-dubious acts–what Haidt and Arizona State University psychologist Carol Nemeroff, Ph.D., call "sociomoral disgusts." While physical disgust is usually pretty similar around the world, sociomoral disgust varies widely by culture.
Still, despised acts and the people who commit them can be hated and considered immoral without being at all disgusting. The puzzle for psychologists is to pinpoint where "contempt" leaves off and disgust begins.
DID HITLER HAVE COOTIES?
Would you wear Jeffrey Dahmer's sweater? Adolf Hitler's? How about Saddam Hussein's?
One test for defining or measuring sociomoral disgust is to determine whether an object touched or owned by a "disgusting" person can reliably elicit disgust. A variation on the roach-in-the-potatoes concept, the sweater test suggests that genuinely disgusting people have an ability to "contaminate" objects that they touch or own, and, more narrowly, that this contamination can be perceived as a germ-like threat–a form of "spiritual pollution"–even by someone who knows that no real danger exists. In kindergarten terms, someone is disgusting when rational adults act as if this person has "cooties."
"If we feel contempt for someone, the sweater can't hurt us," says Nemeroff. "But when we feel disgust, we want to clutch our bodies and say, 'Oh god, I don't want it near me.' It is disgusting when there is a spiritual threat, a sense of horror at the idea of the evil person's stuff getting inside of you."
Generally, only those who do things that no normal person would ever do risk being considered, and not just called, disgusting. Says Rozin: "Some serial killers are despicable but not disgusting; they are just regular killers. But by eating his victims' hearts and so forth, Jeffrey Dahmer became disgusting."
CANNIBALS VS. TAX CHEATS
Is there a common link that bridges such disgusting but seemingly unrelated notions as an unflushed toilet, a dead body, a visit to a slaughterhouse, and a neighbor who commits incest or cannibalism?
The answer, insist Rozin and his colleagues, is simple: each area of disgust is, in its own way, a jarring reminder of our animal nature. The things that most disgust us–defecating, dying, giving birth, eating dubious or unclean foods–are the very traits we most conspicuously share with other animals.
Perhaps it's no coincidence that the only body product we generally don't find disgusting is tears–the only one considered uniquely human.
Social disgust operates much the same way, according to Haidt: "If physical disgust is about distinguishing ourselves from animals, then social disgust is about distinguishing ourselves from 'demons.' 'Human being' is a charged category, and we want to keep its boundaries clearly defined. Someone who cheats on his taxes can be human; someone who eats human flesh cannot. Socially disgusting acts are those that reveal that you have inhuman motives."
The reason such reminders of our "animality" are so harrowing may be equally uncomplicated: any reminder of our animal nature is also a reminder of our own mortality. Certainly, we can coolly discuss death and even come to terms with it; indeed, the knowledge of life's precariousness is singularly human. But it is also the most crucial threat to the psyche, and as such must be repressed. No wonder so much of what we find disgusting relates to death and illness: blood, boils, amputations, and mutilations suggest the fragility of life; corpses and body parts simply verify it.
This theory neatly ties in with related research. People who are disgust sensitive also tend to display a greater than average fear of death. Conversely, people who are tough to gross out are likely to score high on measures of "thrill-seeking." Haidt, McCauley, and Rozin have discovered that, in general women, have higher disgust sensitivity than men and tend to score lower on "thrill-seeking" tests. Another correlation involves neuroticism and psychoticism: individuals scoring high on tests for the former tend to be more disgust-sensitive than normal; those scoring high in psychoticism, less than normal. The probable explanation: neurotics, who tend to be oversocialized, are likely to be very concerned with social customs, traditions, and the like–things distinctly human. A genuine sociopath couldn't care less. Researchers have also discovered a correlation among disgust "domains"–people who are grossed out by holding a dead cat also tend to be very unhappy to find a B.M. left unflushed in a public toilet.
Surprisingly little is known, however, about why such things repulse some people more than others. It does appear that sensitivity to disgust runs in families, says Rozin. "Food preferences are not well transmitted in American families–if parents like broccoli, that doesn't tell you much about their kids. But if the parents are disgust sensitive, that does tend to get passed on."
Brain physiology may also play a role. A team of British and German scientists recently reported that patients with Huntington's disease show a remarkable inability to recognize expressions of disgust, yet can identify other expressions with ease. Huntington's, an inherited disorder that impairs muscle movement, ravages a brain region called the basal ganglia–one of two brain areas activated when healthy people see expressions of disgust. The other, the anterior insula, also plays a role in taste, hinting at disgust's origins in taste rejection. "Who would have expected dedicated brain areas for [recognizing] disgust faces?" asks Rozin.
But there's more. A third part of the puzzle–which Rozin finds most surprising of all–is that the ability to identify expressions of disgust is also impaired in people with obsessive-compulsive disorder (OCD). Given that OCD patients are often obsessed with cleanliness, however, one might expect them to be more sensitive to disgust, not less so. Rozin admits that it's not clear what to make of these unexpected findings–but he suggests that they may be precursors to breakthroughs in how we conceptualize disgust.
The brain's role in disgust isn't the only area ripe for exploration. Rozin, for one, is eager to discover whether a deadening of disgust in one domain also extends to others: "Hospital orderlies, for example, must deal with body waste and death on a regular basis. Does that affect their sensitivity towards food or interpersonal disgust? We don't know." He also remains intrigued by the abilities of people to suspend or frame their sense of disgust, depending on the context. "The smell of decay coming from a house in France could either be ripe cheese or a lavatory. Whichever you think it is will make a big difference in how you react to the odor."
Perhaps the greatest area remaining to be explored is the cross-cultural aspect of disgust. "Certain cultures, like India, have muted core and animal origin disgusts and exaggerated moral and interpersonal disgust," Rozin notes. This means the focus of disgust is on social relations, such as those between members of different castes; protecting the body from "core" disgusts is of less concern. (In the 1970s, a prime minister of India became infamous in the West for waking up each morning to a glass of his own urine.) The example of India suggests to Rozin that the central role assigned to fear of animal origins in the study of disgust will have to be revisited. "Remember, if you believe in reincarnation, then animal origins and death itself don't hay. the same status."
But while value-free disgust might be the explicit social and political aim of our society, we also clearly do still moralize about what we consider disgusting or off-putting--generally areas of personal hygiene--and, in some areas, like obesity and smoking, we have actually begun--in a somewhat medieval way--to re-link disgust to morality.
Another example is vegetarianism; in a recent study published in Psychological Science Rozin and two colleagues found that moral vegetarians--those who gave up the consumption of animal products for ethical reasons--find meat more disgusting than do vegetarians who shun meat for health reasons, even though both groups report liking the taste and smell of meat equally.
In the millennia since mankind domesticated itself, disgust has grown from a reflexive avoidance of unpleasant tastes into something much deeper. It has become an emotion as abstract and complicated as love and as uniquely human as guilt. We are socialized by our disgust and, in turn, use it to socialize others; what better way is there to stop people from doing something socially undesirable than to "make" that something--whether eating rancid meat or, in India, defying the caste system--disgusting.
In fact, this dual life makes disgust perhaps the most paradoxical of emotions. As disgust pioneer Andras Angyal argued, our ability to be disgusted reminds us that our emotional lives remain deeply influenced by "primitive, archaic meanings." "But," adds his heir Rozin, "it is also of course a great sign of civilization."
However much it marks our humanity, our capacity for disgust signals our continuing denial of the animal interiors we carry within our human hulls. The drunken banker on the plane caused a scandal not because he had been a nuisance or even because he had threatened his fellow passengers with illness. He caused a scandal because he, a supposed paragon of man's advanced state, had acted like an animal. And lurking within the recognition of our animal selves is the realization that, like the cattle we consume and lord over, some day soon we will all die.
And that's worse than just gross. It's downright terrifying.
How Much Can You STOMACH?
Some of us are grossed out at the sight of a rat, while others cheerfully enjoy a midnight showing of Night of the Living Dead. Where do you stand? To find out, take the disgust test below, an abbreviated version of a scale developed by psychologists Jonathan Haidt, Paul Rozin, and Clark McCauley. (For the full version of the test: http://wsrv.clas.virginia.edu/~jdh6n/publications.)
Circle T (true) or F (false):
T F 1. It bothers me to see someone in a restaurant eating messy food with his fingers.
T F 2. It would not upset me at all to watch a person with a glass eye take the eye out of the socket.
T F 3. I never let any part of my body touch the toilet seat in public restrooms.
T F 4. It would bother me to see a rat run across my path.
T F 5. I think it is immoral to seek sexual pleasure from animals.
T F 6. If I see someone vomit, it make me sick to my stomach.
T F 7. I might be willing to try eating monkey meat, under some circumstances.
T F 8. It would bother me to see a human hand preserved in a jar.
T F 9. It would bother me tremendously to touch a dead body.
T F 10.I probably would not go to my favorite restaurant if I found out that the cook had a cold.
T F 11. It bothers me to hear someone clear a mucuousy-throat.
T F 12. It would bother me to sleeping a nice hotel room if I knew that a man had died of a heart attack in that room the night before.
SCORING: Count the number of Fs you circled on questions 2 and 7 and the number of Ts circled elsewhere. The average score for U.S. males is five; for females, seven. A higher score means you're more sensitive than average to disgust.
Hey, It's the Best Part
You've surely heard the story of the important diplomatic dinner in a faraway land that culminates in the Western guest of honor being treated to the country's culinary piece de resistance. As the banquet hall goes quiet and all eyes go toward the head table, some impossibly repulsive dish--a bowl camels' eyes, or a baked Airedale terrier--is dramatically placed in front of the visitor who smiles limply, takes a deep breath, and prepares to chow down.
Two things make this tale a classic. The first is that many of us would risk causing an international incident rather than eat something that is in reality perfectly harmless. The second is how powerfully the smoking Airedale prejudices our impression of the hosts; by relishing something we consider gross, an otherwise well-regarded culture can be instantly relegated to barbarian status. What, we ask is wrong with these people? But a better question to ask might be: what is wrong with us?
Most cultures consume only a small subset of potential foods. But we North Americans are almost pathologically narrow in our tastes. For example, we almost totally avoid insects and reptiles, shy away from invertebrates, and, with the exception of a handful of herbivores like chickens and cows, pass on virtually all of our bird and mammal friends. And of these few unlucky finalists, we tend to either eat only a few "choice" parts or disguise the spurned bits in the form of, among other things, hot dogs and Spam.
University of Florida anthropologist Marvin Harris, Ph.D., author of several books on eating, notes that food aversion is generally based on habit, and habit on need. "Insects are not on our menu because they are a poor source of proteins and other nutrients--you really have to eat a lot of them--and because we have so many alternative food sources." By taking a given food off the menu for a while, he notes, it becomes alien and suspect: "When you don't eat things, you end up regarding them with disgust."
How do we, as individuals, become narrow in our eating habits? By age seven or eight, children learn--or are taught--what foods to consider disgusting and in what combinations palatable or even scrumptious foods become disgusting--say, when mashed potatoes are coated with chocolate sprinkles. And clearly our experiences condition us to avoid certain foods; just ask anyone who has taken a swig from a beer bottle at a party and found it fouled with a soggy cigarette butt. A bad experienced like this can ruin our enjoyment of a potential food of beverage for a lifetime. But even beyond such incidents, there is a logic to our narrow eating habits, according to Alexandra Logue, dean of the School of Liberal Arts and Sciences at Baruch College and author of The Psychology of Eating and Drinking, "Liking things that are familiar also means liking things that you've eaten and that haven't made you sick."
However, says Haidt, this does not explain why, in a culture of abundance, we choose to be so picky. "I don't think you can understand human or cultural food choices--especially about meat--by thinking about rationality and practical matters. A lot of it follows a symbolic logic." For example, Haidt notes that Kosher rules make sense if you know an animal's habits. "Any animal that eats garbage or hangs around corpses or feces is likely to be considered disgusting."
Moreover, we tend to avoid foods that call to mind our own beastly pedigree. So there go the heads, eyes, lips, testicles, and so forth--everything that reminds us of us. And the animals that we do eat tend to be shrouded by layers of disguise and deception: cooked even when safety and tastes doesn't require it, called names that obscure their origins--"veal," "venison," and "pork" instead of cow, deer, and pig--and hidden while alive from those about to chow down.
Think of it: freshly-picked strawberries are great, but who wants to fry an egg laid in front of you or broil a steak hacked from a cow you've just seen slaughtered?
Far from being merely silly, however, our weak stomachs and obsessions can deprive us of the diversity of foodstuffs our bodies need. We tend to fear new foods, even those that can contribute to good health, notes George Armelagos, a professor of anthropology at Emory University and the co-author of Consuming Passions. Yet virtually every culture eats something that other cultures would find intolerable. The best approach for the culinary cautious, according to Elisabeth Rozin and others, is to integrate these potentially strange foods into the diet by preparing them in a familiar way. The Chinese, Armelagos says, have been especially successful at this by adding each new ingredient into their stir-frys. "We, he adds, "do it with past."
But if disgust sometimes hinders the search for variety, says Armelagos, it can also drive it. "Try eating the same simple, bland dish--plain white rice or mashed potatoes--for a week. By the end it will seem as repulsive as almost anything you can imagine."
In fact, for all our famed rigidity, American are beginning to loosen up. Two decades ago, who would have thought that yogurt and sushi--one, a gloppy concoction of milk and live bacteria, the other raw fish wrapped in seaweed--would become dietary staples for millions of Americans? Indeed, the American melting pot is accelerating this trend: a recent visit to a supermarket in New York's Chinatown found scores of non-Chinese shoppers cautiously scanning products that at some earlier time might have caused them to call the police--giant clams with "feet" the size of cucumbers, ox penises, duck tongues, squid juice, chicken uteruses, and, beckoning from the front window with welcoming smiles, flattened and cured whole pig faces.
Before you shout "Never!," think about how grow some of our own delicacies would seem if we have not been conditioned to exalt them. Take honey. We enjoy it so much that we call loved ones by its name. But what is it? A gooey substance secreted by insects. And as for the much-worshiped lobster, just three words: giant sea roach.
So if you find yourself at the banquet when the mystery dish arrives, go ahead and dig in--the only thing you have to fear is fear itself. Hell, you might even like it. After all, someone there thinks it's the best part.
Page 8: G. Jacobs, Stennis Space Center/Geosphere Project/Science Photo Library
Page 9: Chip Simons (top), Paramount/ Neal Peters Collection (bottom), AP Photo/Mark Lennihan (left)
Page 10: Allen Wallace/Photonica
Page 12: Carl Vanderschuit/FPG International
Page 14: Chip Simons
Page 16: Superstock (top), Telegraph Colour Library/FPG International
Page 18: Paul Barton/The Stock Market
Page 20: Stephen P. Parker/Photo Researchers, Inc. (top), Steven Needham/Envision (left), Custom Medical Stock Photo Inc. (bottom)
Page 22: Charles D. Winters/Photo Researchers, Inc. (top), Chris Everard/ Tony Stone Images
Page 88: Susie Cushner/Graphistock
PHOTO (COLOR): The mystery of disgust
PHOTO (COLOR): The Origin of Disgust
PHOTO (COLOR): Revolting Problem
PHOTOGRAPHY OF ALLISON LEACH