by John McQuaid
In 1660, a young man named Thomas Tryon set sail from London for the British colony of Barbados, then a growing center of the New World’s booming sugar industry, joining thousands of Englishmen then risking everything to move across the sea to get rich. Tryon was not an entrepreneur, however, but a seventeenth-century flower child. He hated the excesses of the modern world and fancied himself a philosopher of food, out to foment a peaceful revolution that would tame cravings and gluttony and make his followers right with God. Apprenticed to a London hat maker as a young man, he dabbled in herbalism, magic, and alchemy. He also tried silence and asceticism, starving himself to observe his body’s reactions.
The New World captured Tryon’s imagination. To most, it symbolized paradise, a Garden of Eden, wild and pure. Tryon saw it differently: a place where the natives lived in perfect harmony with nature. The reality shocked him. The hillsides of Barbados had been stripped of trees, bushes, and brush; stands of sugarcane rose in their place. Twenty-five thousand African slaves worked this giant sweetness machine. During the harvest, they roamed the fields with machetes, slashing down stalks, stacking and hauling piles of cane weighing hundreds of pounds. In makeshift sheds, water-powered mills with three giant rollers set on end crushed cane stalks fed into them by sweating laborers. The work was tricky: if a man slipped up, fingers or limbs and sometimes entire bodies might be pulled into the rollers and crushed; an ax was kept handy for emergency amputations. Workers lugged buckets of juice to the boiling house, where dried-out cane stalks and other detritus were kept burning around the clock under copper kettles. A master refiner kept an eye on the pots as they boiled and filtered the soupy brown syrup into smaller kettles. To keep the sheds from bursting into flame, the roofs were periodically doused with water. Finally, crystallized sugar was dried, packed in 1,500-pound barrels, and hauled by donkeys to Bridgetown harbor. There, sugar barons, merchants, and servants mixed with vagrants, ex-prisoners, and rum-swilling lowlifes. Yellow fever epidemics routinely claimed hundreds of lives; bodies were thrown in a bog at the edge of town, which belched horrible odors that hung in the air.
Tryon spent five years in Barbados as a milliner before returning to London. His experiences continued to preoccupy him. Nearly twenty years later, he began to write pamphlets espousing a passionate, proto-vegan philosophy. He denounced the sugar plantations as monuments to greed and gluttony, and sweets as temptations that obstructed the digestive tract. Like the ancient Greeks, he believed that the basic tastes of salty, sweet, sour, and bitter defined a man’s character. Tastes “can readily open all the doors and secret gates of Nature’s Cabinets,” he wrote later; the flavor sense was “the prince, king, or complete judge over Life and Death.” Overindulging the appetites ultimately led to damnation. Tryon’s words and arguments influenced the abolitionists (though he was too much a traditionalist to argue for the abolition of slavery). His views shaped an entire vegetarian movement: Ben Franklin gave up meat in his youth after reading Tryon’s writings.
But Tryon was fighting inexorable forces. The foundation of a global sugar behemoth had been laid. From the seventeenth century on, rivers of granulated sugar flowed from Europe’s Caribbean and South American colonies to the larders of kings and, for the first time, into the homes of the middle and lower classes. Food grew sweeter. French chefs began inventing sweet dishes—pies, mousses, pastries, and puddings—that were now separated from the main courses and served as a meal’s finale. The word “dessert,” first used in the seventeenth century, comes from the French word desservir, literally to “un-serve,” or to clear the table when dining concludes. In Tryon’s England, desserts were still regarded as a French abomination, but a few decades later they became standard fare. People began sweetening imported drinks previously taken straight: hot chocolate from the New World, coffee from Africa, and tea from China. In Britain, annual per capita sugar consumption grew from four pounds in 1700 to eighteen pounds in 1800, and then to ninety pounds in 1900.
Between bakeries and rum distilleries, Big Sugar became a major employer, and was soon part of the bedrock of English culture. Near the end of his life, Thomas Tryon was finally seduced. He endorsed sugar, and the plantations he had once condemned. “It spreads its generous and sweet influences through the whole nation,” he wrote. “And there are but few eatables and drinkables that it is not a friend to, nor capable to confederate with; and upon the whole, there is no one commodity whatever, that doth so encourage navigation, advance the King’s customs, and our land, and is at the same time of so great and universal use, virtue and advantage as this King of Sweets.”
The Buddha’s humble snack had embodied moderation and balance in a world where temptation was growing. With Tryon’s conversion, excess had won. In the three centuries that followed, the sugar system expanded inexorably. After the British blockaded France in 1806, halting sugar imports, Napoleon turned to an obscure white root grown and refined in a small part of central Europe. Like cane, the sugar beet contained sucrose, but unlike cane, it grew in cold climates. Napoleon invested a million francs to train farmers and refiners, and another global sweetness industry was born. More than a century later, in 1957, two scientists working for the Corn Products Refining Company of Argo, Illinois, found a way to convert the glucose that makes up cornstarch into far-sweeter fructose, creating high-fructose corn syrup. The United States is the world’s biggest corn producer, and corn syrup can be pumped directly into food factory vats. By the 1970s, corn syrup became a standard food additive.
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The world is now running a giant sweetness experiment. Enormous resources are employed, year after year, to saturate billions of living bodies with sugars, and scientists are only beginning to assess the effects on human biology and public health. What is it about sweetness that exerts such an irresistible attraction? To put the question more broadly: What makes any food tasty, and why? What biological purpose do such pleasures serve, and how do they slide so easily into overindulgence?
Sweetness is the most basic form of tastiness, and of pleasure itself. It is an ancient phenomenon. In evolutionary terms, it seems to be a force existing prior even to sex. Eons ago, single-celled organisms may have clumped together in order to consume more sugar faster, possibly the first event in the evolution of complex life. Fruit flies, whose ancestors branched away from those of humans during the Cambrian explosion more than 500 million years ago, have a similar taste for sugar and the behavioral programming to unerringly guide them to it. These primitive urges still echo in the pleasure Homo sapiens take from sweetness and anything tasty. Without it, meals would be lifeless collages of flat sensations.
Like the ancient Greeks, modern scientists often dismissed the pleasures of food, and pleasure generally. Early in the twentieth century, most believed it was feelings of discomfort that really mattered. They were what drove people to action: hunger led to eating, thirst to drinking, and lust to sex. Touch boiling water and the hand jerks back. The psychologist and philosopher William James summed up this thinking in a letter to a friend in 1901: “Happiness, I have lately discovered, is no positive feeling, but a negative condition of freedom from a number of restrictive sensations of which our organism usually seems the seat. When they are wiped out, the clearness and cleanness of the contrast is happiness. This is why anaesthetics make us so happy. But don’t you take to drink on that account.” In other words, the absence of discomfort is the only true pleasure.
In the 1920s, Sigmund Freud formulated a similar idea that primal drives push humans to seek sexual release. Twenty years later, behavioral psychologist Clark Hull devised the drive-reduction theory: when stressed or frustrated, a human or animal will take action to make the bad feeling stop, then try to avoid it in the future.
These assumptions all shared a rather dreary view of the human condition. They soon faced a challenge. In 1950, James Olds, a thirty-one-year-old psychology postdoctoral fellow at McGill University in Montreal,
decided they were out of step with everyday experience. If chronic discomfort or pain was the key to all behavior, it implied that the best things in life meant nothing. He believed pleasure and happiness deserved to stand on their own.
“For an organism that seeks novelty, ideas, excitement, and good-tasting foods, the drive-reduction theory was a Procrustean bed,” Olds wrote, referring to the myth of Procrustes, a son of the Greek god Poseidon, a rogue smithy who forced his guests to fit in his iron bed by amputating their limbs. “Whatever did not fit was shorn from our image of the man and the rat. Drugs, good foods, and sex were thought of in terms of a need—that is, a hurt generated by withdrawal.”
At the time, it wasn’t clear to anyone how the brain produced a sensation of tastiness or gratification, or why. Olds set out to invent a science of pleasure. He’d had his initial insight while doing an experiment with an albino lab rat. The rat was in a specially designed box, three feet square, its sides a foot high, called an operant conditioning chamber, or a “Skinner box,” after its inventor, B. F. Skinner, a founder of the school of behaviorism early in the twentieth century. Behaviorism was an alternative to Freudian psychology, with its focus on hidden motivations. Skinner believed it was more scientifically rigorous to leave the mind out of it. His box reduced behavior to its essence: an animal was placed inside it, a stimulus introduced, and the response observed. The typical stimulus was either a punishment, such as a mild electric shock, or a reward, such as sugar water. But Olds had found a way to skip over those and go straight to the place in the brain where pleasure and pain were thought to form.
Working with his colleague Peter Milner, Olds had surgically threaded an electrode into an area in the rat’s brain near the hypothalamus. The wire ran to the ceiling, where it connected to a stimulator activated with a button. Pressing it would instantly trigger some kind of reaction in the brain—whether a flood of pleasure, a jolt of pain, or some other sensation or emotion, Olds didn’t know.
He decided to stimulate the rat each time it entered a corner and see how it responded. The first time, the rat circled back to the same corner; it seemed to like the stimulation. Olds hit the button again. The rat returned to the corner much faster. The third time, it stayed put, waiting expectantly for more.
At first, Olds thought he might have discovered the source of curiosity; the rat returned to the corner because it was intrigued. But when he modified the box so that the rat could stimulate itself by pressing a lever, it displayed no adventurousness at all; it just sat and pressed repeatedly. The electrode seemed to make the rat feel good. This effect proved very, very powerful. The rats in Olds’s experiments ignored sugar solution, food, water, and the chance to mate in order to press the lever. In one experiment, they pressed until they nearly died of starvation and thirst. In another, they ran across the floor of a box wired to deliver shocks to their feet in order to hit the switch. He positioned electrodes in slightly different places to map presumed pleasure-related areas in the brain. Stimulating one area made rats eat ravenously, while another made them lose all interest in food.
Eating and drinking proved the easiest behaviors to manipulate. “The ‘rewarding’ parts of the brain,” Olds wrote, “were all related to olfactory mechanisms and to chemical sensors.” Flavor and pleasure were, on some level, one.
Olds’s discovery was dubbed the “pleasure center.” It was a stunning advance, and scientists wondered if the same brain structures that drew pleasure from a spoonful of sugar might also be the source of sexual gratification, or the satisfactions of a lively conversation or finishing a good book. The media debated the potential advantages of this insight. Perhaps the terrible personal and social scourges of unhappiness and depression, not to mention the suffering that defined the human condition, could be cured with the flick of a switch.
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But it wasn’t quite that simple. In 1987, Kent Berridge, then a thirty-year-old junior faculty member at the University of Michigan, was working on an experiment with rats when he noticed something that bothered him. When rodents taste something sweet, their faces and mouths react in a characteristic manner, gaping a bit and flicking their tongues from side to side, as if licking their lips. This is their version of a smile, a clear outward sign of the inner experience of yumminess. The rats had been given a drug to shut down their pleasure centers, and became logy and indifferent as expected. But they also still licked their lips at the taste of sugar—apparently, they were enjoying themselves, though that was supposed to be impossible. At first, Berridge shrugged this off as probably trivial.
Berridge’s grinning rats had been given a drug to block a powerful brain hormone called dopamine. In the years since Olds’s experiments, it had been identified as the chemical that powered the pleasure center. Dopamine is a neurotransmitter, a hormone that the brain employs to send messages in concert with firing neurons. Neurotransmitters facilitate everything from movement to emotions. In Olds’s day, dopamine was an obscure brain chemical, thought to be a building block of more important hormones, adrenaline and noradrenaline, with no apparent function of its own. Scientists first grasped its importance in the 1960s when they discovered that it was essential to voluntary movement—in fact, it’s the dying off of dopamine-generating neurons that leads to the tremors and paralysis of Parkinson’s disease. Biologist Roy Wise later found that rats given dopamine-blocking drugs displayed precisely the opposite effects of a pleasure electrode. The rats slumped into utter indifference. They stopped eating and drinking; sweetness and all other pleasures lost their allure.
Wise proclaimed dopamine the pleasure chemical, and the scientific community followed suit. “The dopamine junctions,” he wrote in 1980, “represent a synaptic way station . . . where sensory inputs are translated into the hedonic messages we experience as pleasure, euphoria, or ‘yumminess.’”
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Berridge reran his rat experiment. The results were the same. So he began to search for an explanation for why dopamine-free animals could still savor the taste of sugar. He wondered if Wise was wrong. (The two of them were collaborating at the time, so it was a bit awkward.)
One obstacle he faced was that, beyond its facial expressions and behavior, a rat cannot explain how it feels. While researching old pleasure electrode experiments, he found an intriguing way around that problem. Between the 1950s and 1970s, doctors at Tulane University in New Orleans had implanted electrodes in the brains of human volunteers. Most had severe forms of mental illness; researchers hoped that brain stimulation would alleviate their symptoms. (Today, a more exacting variant of this technique, deep brain stimulation, is used to treat severe depression.)
The experiments were revealing, helping psychologists map the sources of behavior and emotions in the brain’s anatomy. But they were sometimes spectacularly wrong-headed. In one, psychiatrist Robert Heath implanted nine electrodes in the brain of a young man, code-named B-19, who was severely depressed and had not responded to either drugs or talk therapy. He was also gay, and one aim of the treatment was to “cure” him; therapies included viewing a stag film, and a two-hour visit from a female prostitute.
With so many curling wires dangling from his skull, B-19 looked like a cyborg, and in a way he was: he became a kind of electronic puppet pulling its own strings. Heath gave him a button to activate the electrodes. One was placed in the pleasure center. And sure enough, when a small jolt was administered there, B-19 acted just as the rats had. He kept punching the button: during one three-hour period he hit it 850 times. He reported a strange mix of feelings: self-confidence, relaxation, and arousal. When the lab technicians started to disconnect him, he begged them not to. The electrode also made him want to have sex with both men and women, leading Heath to think he’d found a potential cure for homosexuality. After several weeks of experiments, the electrodes were removed and B-19 was released. Heath followed his progress for eleven months. “While he looks and is
apparently functioning better, he still has a complaining disposition which does not permit him to readily admit his progress,” he wrote. Following his release, B-19 held a number of part-time jobs, had a ten-month sexual relationship with a married woman, and told Heath he had twice turned tricks with men to make money.
Reading these descriptions, Berridge noticed something. The electrodes were assumed to be stimulating eruptions of dopamine in B-19’s brain—yet he never seemed to enjoy himself. He became sexually aroused, but never had an orgasm. He never said “oh, that feels good!” Hitting the button led only to more anticipation. Perhaps dopamine did not really create pleasure after all, Berridge thought, but rather the craving for it. Once, scientists had dismissed pleasure’s importance. Now, they might be mixed up about what caused it.
Searching for alternative pleasure chemicals, Berridge looked to addictive drugs. Opioids such as morphine and heroin evoke feelings of euphoria. Perhaps the answer was the brain’s own natural opioids, also known as endorphins. In the early 2000s, nearly two decades after his initial discovery, he tracked intense pleasure reactions to endorphins in two areas of a rat’s brain, the nucleus accumbens and ventral pallidum. He named these “hedonic hotspots.” These tiny clumps of neurons, about the size of the head of a pin, are the only brain structures known that directly cause pleasure.
