Tasty (15 page)

Disease poses a constant threat to groups. Unlike toxins in food, diseases have many different avenues of attack. Bacteria and viruses spread invisibly through food, physical contact, and insect bites. Early humans would have recognized the warning signs of possible infection: spoiled food, a festering wound, fever, a rash, vomiting. These would have evoked the earliest forms of a new, more expansive kind of distaste.

Valerie Curtis, a biologist at the London School of Hygiene & Tropical Medicine, devised a clever way to detect echoes of this ancient transformation amid the buzz of modern life. In 2003, she posted twenty photos of random people and objects to a BBC website. Visitors rated each photo's disgustingness on a scale of zero to five. Seeded among them were pairs of similar images, of which one had been altered to suggest dis
ease. A picture showed a dish of blue liquid; its counterpart depicted what appeared to be pus and blood. Another photo showed a man's healthy face. In the altered version his skin was spotty, and he looked feverish. To suggest infection, Curtis included a photo of an empty subway car and one filled with people. Nearly forty thousand people around the world weighed in. Unsurprisingly, a majority found the disease-­related images more disgusting, women more so than men; Curtis thinks such heightened sensitivity may have helped early human females protect babies and young children from sickness. A separate study by UCLA anthropologist Daniel Fessler found that women grow even more easily disgusted during the first trimester of a pregnancy, when their immune systems weaken to avoid attacking the fetus. When the risk of disease rises, the brain and body respond with heightened alertness.

As people age, their vigilance declines. The older the participants in Curtis's study were, the less offensive they found the disease photos. Curtis believes that this is because old people are less likely to reproduce, and so have less need, from the standpoint of natural selection and the group's survival, to watch for the warning signs of disease. Curtis also asked people to rank the person they'd least like to share a toothbrush with, from a list including “postal carrier,” “boss,” “TV weather forecaster,” “sibling,” “best friend,” and “spouse.” The more tenuous the bond, the more disgusting this idea was. Strangers pose a greater risk of disease to the unexposed immune system than friends or relatives do.

Curtis dubbed this suite of responses the “behavioral immune system.” It's a set of cues blending the senses with group dynamics. These habits were built on observation, forbearance, and ultimately, success. Over the eons, the behav
ioral immune system would have constantly altered and expanded its contours to meet endless, changing threats. As the “yuck” face was applied to new things and situations, people would have combined it with language and gesture, creating an expanding expressive repertoire.

• • •

Distaste and the “yuck” face are the products of an ancient circuit of firing neurons, blood flow, and neurotransmitter activity in the brain that includes the insula and orbitofrontal cortex. Disgust uses the same circuit. But it has adapted this wiring for new purposes. A pleasant, easygoing man whom scientists dubbed Patient B. helped illuminate the inside of this black box.

In 1975, when Patient B. was forty-eight years old, he contracted a severe form of encephalitis, an inflammation of the brain caused by an infection of the herpes simplex virus. B. fell into a coma for three days, then awoke and gradually improved before being released from the hospital a month later. But B.'s brain, and his mind, were badly crippled. The infection had ravaged structures involved with memory and emotion, including the amygdala and the hippocampus of each hemisphere. He could remember events and dates from his childhood, but almost nothing later. He lived in a constant present, holding on to new facts for only forty seconds. His knowledge was mostly generalities: he couldn't recall his own wedding, but he knew what a wedding was. Nevertheless, those meeting him for the first time might not immediately detect a problem. He seemed happy. He laughed often, was an avid checkers player, and welcomed the neuroscientists who lined up to run tests on him. He enjoyed the mental challenges they provided.

Patient B.'s oddest quirks had to do with flavor. Parts of his insula and orbitofrontal cortex had been destroyed. He couldn't tell the difference between salt water and sugar water. He'd drink both with a smile, and would choose randomly if told to indicate the one he liked better. B. did have some taste perceptions, but they were mostly unconscious. In a 2005 experiment conducted by neuroscientists Ralph Adolphs and Antonio Damasio, B. was presented with salt water and sugar water, this time colored red or green. This changed everything. He was told to sample both and choose the one he liked; eighteen out of nineteen times he chose the sugar water. When asked to sip the saline solution, he vehemently refused. The colors created—or revealed—a preference for the sugar solution, without any awareness of or appreciation for the sweetness itself. Adolphs and Damasio theorized that there were undamaged parts of B.'s brain that could tell salty from sweet, but they were cut off from the damaged, conscious ones. Like a marooned man firing a flare gun to alert a passing ship, the colors allowed this part of the brain to signal its true feelings to the outside world.

B.'s sense of distaste was practically broken; so, unsurprisingly, was his sense of disgust. He had forgotten what disgust was, or even that it existed. He tossed back a cup of pure lime juice and pronounced it “delicious.” When read a story about a person vomiting, B. said he imagined the person feeling hungry or delighted. Experimenters acted out facial expressions for him. B. recognized some of them, but identified disgust as “thirsty and hungry.” When one of the researchers chewed some food and spit it out, making retching sounds and “yuck” faces, Patient B. again labeled the food “delicious.”

Patient B.'s brain was too badly damaged to pinpoint
precisely where and how the disparate functions of feeling, imagining, and recognizing disgust came together, so neuroscientists embarked on a search. It led them to a familiar spot. In one experiment at France's National Centre for Scientific Research, fourteen volunteers had their brains scanned while they viewed movies of people reacting as they sniffed a glass containing a disgusting, pleasant, or neutral liquid. Then the fourteen were scanned as they did their own sniffing, and the results compared. The scans showed that observation and experience overlapped in only one spot: the anterior (forward) part of the insula, the area that processes tastes. It's also a place where inner feelings and outward, empathetic responses unite.

Feeling and observing disgust generate similar patterns of brain activity, and similar feelings. This is a basic form of empathy. Brain scans have shown that the more empathetic a person is, the more sensitive to disgust he is, and the brighter the insula burns. The insula, remember, is also a hub for many of the body's internal states and feelings. Its neurons align the taste system with brain structures that move facial muscles and recognize expressions, evoke memories, and enable speech, imagination, and storytelling. It also contains a distinct kind of neuron found only in the brains of humans, great apes, elephants, and whales and dolphins. Long, spindle-­shaped von Economo neurons cluster mostly in the insula. They transmit messages across much longer distances than ordinary neurons, perhaps to bridge the ever-widening spans around the cortices of big-brained animals. Spindle neurons seem to help interpret and respond to emotional cues, shaping our relationships and social personae.

This means that visceral taste reactions underlie our most sophisticated behavior, animating our thoughts and judg
ments about everything from politics to money. Psychologist Hanah Chapman of the University of Toronto wanted to test this idea. She did an experiment in 2009 that focused on twinned muscles on either side of the mouth and upper lip that contract when a grimace is made, wrinkling the nose, called the levator labii. In the first phase, electrodes measured the muscles constricting in response to bitter drinks and photos of feces, injuries, and insects. Chapman then reran the experiment, this time with volunteers playing the Ultimatum game. Two players have a ten-dollar sum: one proposes how to split the money, the other decides to accept or reject the offer. If accepted, the money is split accordingly; if not, neither gets anything. Players rated their own emotional responses to the offers and outcomes as their facial muscles were monitored. As the offers grew more unfair, people became disgusted, their levator labii muscles twitched, and they were more likely to reject the offer. When their counterparts offered only one dollar out of the ten dollars, the contractions spiked.

The signal was clear: unfairness evoked the same muscular twitch as tasting something terrible. Rather than triggering anger, violating the everyday moral code of fairness led to revulsion, and to rejection of the unfair offers—and of the people making them. Taste had morphed into a primitive form of morality.

In the 1980s, Paul Rozin, a professor of psychology at the University of Pennsylvania, became fascinated with these gradations of disgust. At the time, no one else in his field was interested; the topic was considered marginal, a dead end. He decided to pursue it anyway. In a 1985 experiment, Rozin examined how the sense of contamination—the same feeling Darwin experienced when the Yahgan man touched the meat in his tin—emerges in children.

Rozin juxtaposed apple juice with a comb, and cookies with a dead grasshopper. Each pair of items was presented to a group of children aged three to twelve and a half, along with a scenario intended to provoke a particular degree of disgust.

First, a researcher told the children they could drink the juice after she stirred it with the comb. In one test, the comb was brand-new. In another, the volunteers were told it had been used but washed. In the third version, the story went, the comb had just been used on the researcher's own hair. Next, a dead grasshopper was placed next to a plate of shortbread cookies. The researcher sprinkled green sugar on the cookies, saying it was made from ground-up grasshoppers but tasted just like sugar. Finally, the experimenter poured some more juice, took out another dead grasshopper, and dropped it into the cup. It floated. She offered the child a straw and said, “Would you like to drink?”

The older the children, the more likely they were to reject the contaminated object. Eighty percent of the kids between three and six drank from the glass supposedly stirred with a used comb, but only ten percent of the eldest group. (Though a full 20 percent of this group decided to try the floating grasshopper–apple juice drink; perhaps adolescent daring had come into play.) When the same tests were run on adults, they were even more sensitive. Only five out of sixty-seven children refused the juice stirred with a new comb, while nearly half of adults did.

The sense of disgust evolves over the course of a lifetime. As children grow into adults, their social interactions become more complicated. At the same time, they pick up on social rules. Both of these imprint themselves on the brain. As people reach adulthood, the personal universe of disgust expands exponentially. Rozin and his colleague Jonathan Haidt
divided it into four categories: inappropriate sexual acts, poor hygiene, death, and violations of body norms such as wounds, or obesity, or deformities.

Rozin saw an underlying theme. We hate to be reminded that we are all animals with fragile bodies that bleed, excrete, have sex, and get sick. These things remind us of death. We're the only animals who know death is coming; disgust is one method of averting our eyes from anything that reminds us of that.

Before humans can eat, animals and plants must die. The slaughter and rendering of animals is kept out of sight, and flank steaks, chicken parts, and spareribs appear disembodied behind glass and under plastic in supermarkets, as if by magic. In the United States, only certain kinds of animals are considered acceptable to eat: cattle, pigs, and fish, but not horses, dogs, or rats. Some organs—livers, calves' pancreases in sweetbreads—are delicacies. Others—bladders, hearts, and brains—are repulsive. These rules vary, seemingly arbitrarily, by location and culture. In the American South, pigs' feet are common fare; in Mexico, there's the offal in
menudo
, a tripe soup; in China, almost any part of a chicken is fair game.

In the extreme, entire nations can come to love things that repel outsiders. This makes the line between disgust and deliciousness razor-thin, moving depending on geography, climate, and culture. In Iceland, there's a popular dish called
hákarl
, made from the fermented flesh of the Greenland shark, which is notorious for its foul, ammonia-tainted flavor.
Hákarl
has become a hard-core foodie challenge, which even celebrity chefs routinely fail. Anthony Bourdain called it “the single worst, most disgusting and terrible-tasting thing” he had ever eaten. When Andrew Zimmern, host of the Travel Channel's
Bizarre Foods
, smelled it, he said he was reminded
of “some of the most horrific things I've ever breathed in my life.” But he at least found the taste tolerable. Gordon Ramsay spit it out.

Greenland shark meat is poisonous, a result of its peculiar physiology. Sharks filter out some wastes through muscles and skin rather than in their urine. The Greenland shark retains uncommonly high concentrations of urea, the main component of urine, and trimethylamine oxide (TMAO), a potent neurotoxin that induces a condition resembling extreme drunkenness and sometimes leads to death. During the late Middle Ages, Icelanders solved this problem by burying the meat in the sand, placing heavy stones on top to press the poisons out, and then leaving it for several months, just as the Yahgan did with their whale meat and blubber. As it froze, thawed, and refroze,
Lactobacillus
and
Acinetobacter
bacteria proliferated, producing enzymes that broke down the urea and TMAO. The smell, however, worsened because of two by-products. Urea decomposes into ammonia, and TMAO into trimethylamine, the compound that gives rotting fish its signature odor.