CHAPTER THREE
DISGUST’S DIVERSITY
I believe that when man evolves a civilization higher than the mechanized but still primitive one he has now, the eating of human flesh will be sanctioned. For then man will have thrown off all of his superstitions and irrational taboos.
Diego Rivera, My Art, My Life
Dominating one wall of the Mollien gallery in the Louvre is an impressive oil painting by the French romantic artist Théodore Géricault. Adrift at sea on a disintegrating raft are fifteen figures, some hopeful of rescue, others in despair, others—gray-hued with limbs trailing in the water—already dead. A closer examination of the bottom left of Géricault’s heroic composition reveals the torso of a man, with bearded head, shoulders, and arms, but missing his trunk and legs. Visitors to the Paris Salon of 1819, where the painting was first displayed to huge controversy, recognized this imagery immediately. They had all read newspaper accounts of the French navy frigate Medusa that had run aground off the coast of Africa. With too few lifeboats, 150 people were cast adrift on a makeshift raft. Those who survived endured dehydration, starvation, and madness, and some had resorted to cannibalism.
The Wreck of the Medusa was exhibited in London and drew huge crowds: some perhaps devotees of French romantic art, but most surely lured by the idea of contemporary French cannibals.
The consumption of human flesh is a nasty subject, hard to write about, even for a seasoned disgust researcher. But why this visceral response? If I had been raised in a society where cannibalism was normal, perhaps I wouldn’t be averse to a tasty meal of “long pig.” The apparent cultural specificity of cannibalism seems to challenge one of the main tenets of this book. Surely the notion of eating the flesh of another person should be disgusting to everyone, always and everywhere. And this should be because of our ancient evolved motives; animals that had propensities to eat their cousins also ran the risk of consuming their cousin’s parasites. The more closely related the species you treat as meat, the more likely you are to catch something infective to you.1 The idea of the edible dead should thus be abhorrent to all humans everywhere.
Yet this is a mistaken view of what evolution teaches us about human behavior. Yes, disgust may be a universal, a system in brains that evolved to help us avoid the fitness costs levied by parasites, but this does not mean that disgust works in the same way the world over, from culture to culture, from social group to social group, and from person to person. Though disgust has a main theme, it also has variations. Disgust sensitivity is an aspect of personality, varying between individuals. It fluctuates over the life course, and even by time of day. The specific disgust responses of individuals are influenced by individual experience; those who have had a disgusting encounter with a dead rat may respond more aversively to rats. Those who have had a bout of sickness after eating rotten chicken liver pâté may never want to eat it again.
Further, disgust is only one among many motives in the brain; it can be down-regulated when there are more pressing needs to attend to than disease avoidance. And disgust is not just a matter for the individual; we have hive brains where what others think and do affects what we think and do, and what we think and do about the disgusting, in turn, affects our culture.
While all humans are all equipped with a disgust system, the outputs of the system are not fixed, but flexible, within certain limits. Disgust is thus more than “just” an emotion; it is an adaptive system, natural selection’s elegant solution to the problem of avoiding invisible infection in a range of different contexts.
Disgust Personalities
We have all encountered individuals who are too fastidious to drink from a shared water fountain, just as we have met others who care so little for their own hygiene that they cause offense with their poor manners and their bodily emanations. These personality variations emerged even on the raft of the Medusa. In their account of the disaster, Savigny and Corréard described how many of the raft’s unlucky passengers could not bring themselves to consume the strips of flesh that had been pegged to the rigging to dry.2 Those who could, however, found that it restored their energies, helping them to stay alive until they were finally rescued.
Why did some individuals eat human meat, while others found it too disgusting to contemplate, even at such enormous cost? Like height, disgust is a trait that varies between certain limits. Just as it was disadvantageous to have many of the genes that led to extremely short stature or to terrific height, so it was with disgust. Those ancients who were low on disgust sensitivity, who didn’t worry about eating bad meat or about their bodily hygiene, were weeded out of the ancestral gene pool by disease. And those obsessives who couldn’t tolerate even the slightest contamination of their water or who were too squeamish to touch any body fluids wouldn’t have contributed many of their genes to today’s pool either. They might have died of thirst and would certainly have found the intimacy of reproduction a challenge—let alone coping with changing their offspring’s dirty diapers.
People differ from one other because of phenotypic and genetic diversity in a population. Individuals have ancestors with different numbers and combinations of the genes that contribute to the expression of disgust sensitivity, who lived in varied climes and settings with different levels and kinds of disease threat. Everyone therefore inherits a shuffled deck of genes for particular disgust dispositions, and this is a relatively fixed aspect of our personality.
Like other aspects of our personality, diversity can lead to difficulties. Discrepancies in disgust sensitivity are a major source of marital disharmony—for one partner, sharing a fork is unacceptable, while the other can’t see what all the fuss is about. For one partner showering every day is essential, while the other is content to cultivate interesting odors. No amount of logical argument can persuade one of the other’s point of view. Disgust sensitivity may, in fact, be a component of neuroticism—which is one of the famous “Big Five” dimensions of personality.3 Neurotics tend to succumb more often to anxiety and depression,4 so much so that personality researchers wonder why such an apparently maladaptive trait should persist today. Disgust may offer part of the solution to this puzzle. In our ancestral past, high levels of neuroticism might have led to more infection avoidance behavior, just as it would also have helped people avoid other dangers such as predators and accidents.5 Though we don’t know whether neurotic people are, in fact, better protected from infectious disease, something akin to this phenomenon has been observed in sunfish, Lepomis gibbosus. (Yes, fish do have “personalities.”6) It turns out that shy sunfish carry different types of parasite than bold sunfish, presumably because their behavior affects the type of parasite that they encounter.7
History does not relate whether the lone woman on the raft, a sutler from the south of France, was high on the neurotic scale and was therefore unable to eat human flesh (though we do know that she was in a poor way and was thrown overboard before rescue). She probably had a stronger disgust response than the male castaways (remember that in our BBC web survey women scored disgusting images higher than men on average).8 This could be a fundamental gender difference that reflects women’s differing evolutionary history of responsibility for child care.
Disgust sensitivity may be a trait that is established at conception, but it can still vary over the course of a lifetime. Paul Rozin has documented how children start life with a low sensitivity to disgust,9 only later developing a full-blown disgust response. This may be because disgust is not needed in the first few years of life, when an infant’s exposure to pathogens in the environment tends to be controlled by its mother. Disgust sensitivity rises to a high in young adulthood and then tapers down with age. Teenagers constitute a huge market for hygiene products such as shampoos and deodorants, many of which are marketed as mating aids.10 Again, this peak is probably adaptive, since it is helpful to be sensitive to disease cues during the mating and child-rearing years.
There are other times in the human life cycle when it pa
ys to be especially avoidant of pathogens. Women in their first trimester of pregnancy lower their immune responses because they need to be able to tolerate the implanted egg, with its foreign genetic material. At the same time they become more squeamish about food, body products, and the risk of contagion.11 It seems that there is a trade-off between the immune system and the disgust system; when one goes down, the other is ratcheted up. Indeed, the morning sickness of pregnancy may be a way of protecting both mother and fetus from toxins and infections during this vulnerable time.12
Dan Fessler and his colleague Diana Fleischman found that women tended to ruminate more about disease and contagion in the middle of the luteal phase, one week after ovulation—when immune responses are lowest—and ready to accept a possible pregnancy.13 Cues to disease can also affect the immune system. When Mark Schaller and colleagues in Toronto exposed experimental subjects to pictures of either guns or infectious diseases, the white blood cells of those in the disease condition produced higher levels of interleukin-6, a molecule involved in immune defense.14 The factor that links disgust with the immune system might be the neuropeptide serotonin, which is involved in learned aversions, vomiting, and the modulation of both innate and acquired immunity across Animalia.15 Systems for avoiding and fighting disease may have very deep evolutionary origins indeed.
This cross talk between the disgust system and the immune system may even extend to what happens to an embryo during pregnancy—a subject known as fetal programming, now fashionable among health researchers. It seems that pregnant mice who are simply exposed to an infection, without even catching it, have sons who grow up to be less aggressive than the sons of mothers without the exposure.16 Whether human mothers who have been in contact with disease during pregnancy give birth to less competitive sons, who thus save their energy to better fight off infection, is one of the many questions that remain to be explored by disgustologists.
Trading Off
“Disgustability” may be a trait that is part of human nature, but levels of disgust sensitivity vary with age and with the current state of the immune system. Do other factors influence how disgustable one is? For the survivors of the wreck of the Medusa, the biggest problem was to avoid death by starvation, which was a more pressing problem than the risk of catching an infection from corpse meat. Their disgust responses were thus probably partially suppressed: an adaptive “trade-off” that can be demonstrated in the lab. While ethical review boards don’t permit one to starve one’s subjects or to offer them “long pig” dinners, one researcher asked his subjects not to eat for fifteen hours and then shared pictures of nasty-seeming food (“looking like excrement or vomit”). He found that those who were hungry showed far less disgust, as measured by the activity of the lip-curl muscle (musculus levator labii), than those who had just had their lunch.17
What else might interfere with the disgust system? No one has explicitly examined whether feeling lusty reduces your disgust sensitivity, but a study of decision making and horniness by behavioral economist Dan Ariely suggests that it may. He asked male Berkeley students to imagine that they were sexually aroused and to predict their answers to a series of questions about what they would find attractive. He then asked them to masturbate, without climaxing, and answer the questions again. The students’ predictions and their actual responses did not match up at all. While only 13 percent thought they would find sex with an extremely fat woman attractive in the cool state, the figure rose to 24 percent in the aroused state. Similarly, the idea of anal sex and sex with animals increased in attractiveness by 67 percent and 167 percent, respectively, in the excited state. Twenty-eight percent more students liked the idea of seeing an attractive woman urinate when they were aroused.18 This ability of lust to down-regulate disgust was essential to our ancestors’ becoming our ancestors—given how messy the business of sexual reproduction can be.
The Béarnaise Sauce Effect
The disgust system is a product of evolution, shaped by the hostile environments in which our ancestors evolved. The types of stimuli that were reliably associated with infection—for example, the smell of rotting human flesh, the taste of feces, or the sight of deformity—are innately labeled as disgusting. But parasites don’t always betray themselves so readily. They may lurk in foods that smell fine or in people or animals that seem healthy, and they can spread surreptitiously over suitable surfaces. Faced with this invisible and unpredictable threat, how could the system learn what to avoid? If your disgust system got it wrong, it would mean that your genes would pay the highest cost: elimination from the gene pool. And if you happened to have genes for brains with psychological tricks that could help you infer the presence of dangerous parasites, you would tend to have more, and more successful, offspring, who would pass these genes on.
One of these tricks is known as the Garcia effect.19 When he was a young psychologist working on radiation for the US Department of Defense, John Garcia noticed that rats that had been made sick by radiation were reluctant to drink the water in their cages. He experimented with a variety of foods and showed that the rats became aversive to anything they had consumed around the same time that they fell sick. He showed the same in garden slugs—which avoid carrot juice if it has previously been paired with lithium chloride.20 This clever unconscious mechanism works for humans too—keeping us from returning to foods that have caused nausea in the past. However, as with the rats that mistook the food for the source of the sickness, not the radiation, the mechanism can misfire. The famous psychologist Martin Seligman recounted how he couldn’t eat béarnaise sauce for ten years because of a bout of sickness following a steak meal. He knew that the sickness was probably due to the flu, as all of his colleagues had come down with it too. The intellectual knowledge didn’t help: the associative conditioning had done its work, and every time he saw or thought of béarnaise sauce, it made him feel sick to his stomach.21
The Garcia, or béarnaise sauce, effect is a special case of associative learning—where an emotional memory is created about a particular stimulus. Imagine being offered a new and unfamiliar food on a foreign holiday—perhaps a slice of crocodile meat or an emu steak. Despite all your host’s reassuring words, you’d be unlikely to tuck in with gusto until you had had a careful sniff and perhaps a small nibble. If you detected smells or tastes that you found disgusting, that would be that: polite thanks, but “no thanks.” The primary reflexes of taste and smell decode the complex chemical signals emanating from organic materials that are possible foodstuffs, and hit the alarm signal when they find the signatures of biological toxins or pathogenic microbes. That alarm is recorded as a persistent emotional memory, and every time that same food is encountered, it’s as if it has a flag stuck in it—“avoid this food!” On the raft of the Medusa, one of the castaways tried tasting excrement. The taste was so bad that he couldn’t continue eating, despite his extreme hunger. According to Sigmund Freud, we all try poo tasting in infancy. But we only try it once; after that the warning flag in emotional memory makes sure that we never do it again.
It is not clear whether we come pre-prepared with the ability to discriminate disgusting from nondisgusting odors or not (it’s hard to do such experiments on tiny babies).22 Disgust responses to odors may be present in babies or may emerge later in life, when infants become more independent and need them more, or it may be that we start without them but are especially prepared to learn what is disgusting. Certainly it is hard to separate the two. If you search for videos of disgusted babies on the Internet, you find plenty of disgust reactions, suggesting innateness. However, if you listen to the sound tracks, you almost always hear the parent with the camera exclaiming, “Yuck! Yuck! Yuck!” at the smelly socks or dirty feet that the infants encounter. We seem to be highly motivated to teach what is disgusting to our offspring—another adaptive trait. The PAT of disgust predicts that we should have primary odor reflexes that emerge early, before two years of age, and that we should also be especially sensitive to learn what i
s disgusting from those around us and from experience.
Contagion
As far as we know, we are the only animals that can keep track of the history of disgusting objects.23 Our parasite-detecting X-ray specs not only carefully note where disgusting things are now; they also record where those things have been in the past. So a cockroach that has walked across a sandwich leaves invisible footprints that make the sandwich inedible. It’s hard to wear a stranger’s clothes if we’ve been told that they haven’t first been laundered. Many people feel that they have to wash their hands after using public transport, sensing contamination from surfaces that have previously been touched by multiple strangers. One of the creepiest stories in my disgust collection is that of a woman who bit into her hamburger in a famous burger restaurant chain, only to notice that a chunk had already been bitten out of the other side by some unknown other. Disgusting things like saliva, insects, or strangers leave invisible traces of contamination behind them, painting an indelible taint onto the object that has been contacted.
Perhaps the very reason why we experience the feeling of disgust is due to this need to learn what to avoid.24 Each time we feel disgust, it’s a bad experience that sticks a flag on the offending object, providing a reminder as to what to avoid next time. It’s like a sticky emotional Post-it Note to the self saying, “Don’t touch—bad stuff here.” The associative flags can get attached quickly and easily, but removing them again is a slow process.25 A therapist recounts the story of a man who noticed a discarded Band-Aid stained with blood in a hospital parking lot. Twenty years later he could still remember the exact spot where he saw it and was still avoiding it.26
Don't Look, Don't Touch, Don't Eat: The Science Behind Revulsion Page 5
