In a laboratory in Denver, on a decommissioned U.S. Army base, a baby sits in a high chair with two electrodes attached to his chest. To his left, on a small table, a muffin tin holds four numbered cups, each filled with a green substance. On the walls and the ceiling, four cameras and an omnidirectional microphone record the baby’s every burble and squawk, then transmit them to a secure server in an adjacent room. What looks like a window with blinds, across the room from the baby, is in fact a two-way mirror with a researcher behind it, scribbling notes. The baby’s mother takes a spoonful of the first sample and lifts it to the baby’s mouth, and the experiment begins.

Building 500, as this facility was formerly known, has the looming hulk of an Egyptian temple: it was once the largest man-made structure in Colorado. When it opened, in 1941, four days before the attack on Pearl Harbor, threats to American safety were much on the government’s mind. (After the war, President Eisenhower spent seven weeks on the eighth floor, recuperating from a heart attack.) The Good Tastes Study, as the baby experiment is called, is in a similar spirit. The two electrodes on the baby’s chest will monitor his heart rate and how it fluctuates with his breathing. A third electrode, on the sole of the baby’s foot, will measure his “galvanic skin response,” or how much he’s sweating. Together, they’ll indicate whether the green substance is triggering a fight-or-flight response. Does the baby sense danger?

The enemy in question is kale. The four cups are all filled with raw kale leaves whipped into a smooth purée, or slurry, as food researchers call it. One sample is plain, another sweet, another sweeter still, and the last one salted. Sugar and salt can mask the bitterness in kale, but this baby isn’t fooled. No matter which sample he’s offered, he grimaces and turns his head, purses his lips, and swats the spoon away. The more his mother tries, the grumpier he gets, till he kicks his foot so hard that he jostles the electrode, disrupting the signal. “It’s just a thing that happens,” Susan Johnson, the director of the study and a professor of pediatrics at the University of Colorado, told me. “Completely throws off the galvanic skin response. If you can find a body part that’s not in motion, let me know.”

Most babies could use a dose of kale: a half cup has more than a day’s worth of Vitamins A, C, and K. The only problem is that they hate it—or so parents and baby-food manufacturers seem to assume. Two years ago, when Johnson launched the study, she sent her graduate students to find some commercial baby foods made from pure kale or other dark-green vegetables. They couldn’t find any. The few that did exist were mixed with fruit. “I sort of blew it off at first,” Johnson told me. “I just sent them out again and said, ‘Try harder.’ ” They went to Kroger, Walmart, Whole Foods, and Sprouts; they scoured the organic markets in Boulder, then widened their search to the Internet. Still no luck. The closest thing they could find was a Polish product made with Brussels sprouts. “That’s when I started to get less frustrated and more interested,” Johnson said.

Food preferences are a chicken-and-egg problem. Do we choose them or do they choose us? The Good Tastes Study was designed to tease such mysteries apart. Over the next six months, a hundred and six babies will pass through Building 500 and try the samples. Afterward, two experts in human expression will scrutinize their faces on the videos. They’ll divide their features into zones of activity and classify every twisted lip and wrinkled nose according to a Facial Action Coding System. The system can sort adult expressions into emotional categories: Happiness, Sadness, Surprise, Fear, Anger, Disgust, and Contempt. But baby faces are too pudgy for such specificity, Johnson says, so she’ll settle for positive, negative, and neutral. (When a baby makes a gesture known as “the rake” and claws the kale off his tongue, that’s negative.) She’ll correlate those responses with the electrode readings, compare them with the babies’ reactions to a control substance (oatmeal), and then circle back to see how the parents reacted to their children’s reactions.

Baby food shouldn’t be this hard. After a few hundred thousand years of raising children, humans ought to have this part down. No food has been more obsessively studied, no diet more fiercely controlled, no dining experience more anxiously stage-managed. Yet we still get it wrong. On any given day, a quarter of American toddlers eat no vegetables. When they do eat them, the most popular choice is French fries. Why don’t babies know what’s good for them? And why don’t we?

When my kids were young and peevish and a carrot could cause a revolution—when Ruby loved oatmeal but hated Cream of Wheat, and Hans loved Cream of Wheat but hated oatmeal, and Evangeline wanted no breakfast at all; when every dinner was like the Yalta Conference and the table like enemy terrain, booby-trapped with vegetables that could go off in your face—I took courage from Calvin Schwabe.

Schwabe was a man not easily disgusted. A veterinary epidemiologist at the University of California, Davis, he specialized in parasitic worms that get passed from dogs and wild animals to people and end up in their liver, lungs, and brain. When Schwabe moved to Davis, in 1966, after a decade studying tapeworm infestations in Lebanon and Kenya, he found the local culture a little tame. He was famous for taking grad students to ethnic restaurants and chiding the chefs for not using authentic ingredients. He hosted dinners of grilled guinea pig and deep-fried turkey testicles.

Squeamishness is more than a minor character flaw, Schwabe believed. It’s an existential threat. Even in America, people go hungry every day although they’re surrounded by perfectly nutritious food. Pets, for instance. “Some 3,500 puppies and kittens are born every hour in the United States,” Schwabe wrote in “Unmentionable Cuisine,” his cookbook of taboo foods, published in 1979. “The surplus among them represents at least 120 million pounds per year of potentially edible meat now being totally wasted.” “Unmentionable Cuisine” is a work of calculated outrage, but it’s not “A Modest Proposal.” It’s a practical guide, Schwabe wrote, for the not too distant day when people may have no choice but to eat stewed cat (page 176) and beetles in shrimp sauce (page 372). If we were all just a little less finicky, we could feed the world.

It’s a sensible argument, but then food preferences are rarely amenable to sense. Our tastes are us, we like to think. We were born hating lamb or fermented fish, even if half the world loves nothing better. And it’s true that everyone experiences food differently. The woman beside you on the bus may have three times as many taste buds as you do, and different genes regulating those tastes. Depending on which version of the TAS2R38 gene you have, you may be highly sensitive to bitter foods, mildly sensitive, or not sensitive at all. People with dense, hypersensitive taste buds are often called supertasters, and are said to represent about a quarter of the population. Another quarter, with sparse, insensitive taste buds, are called nontasters, and the rest fall somewhere in between.

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But it’s not that simple. Supertasters don’t always live up to the name—in some studies, they react to food just as regular tasters do—and genetic effects tend to fade. Children who are hypersensitive to bitterness are often especially fond of sugar. But that predilection disappears in adults, while the taste for bitterness grows. Being a finicky eater makes evolutionary sense for a toddler, lumbering around sticking things in his mouth. Better to spit them out if they don’t taste familiar. But we learn to pick our poisons, and then to love them beyond reason. We go from Pabst to I.P.A., milk chocolate to dark, latte to espresso, homing in on the bitterness we once avoided. “Our biology is not our destiny,” Julie Mennella, a biopsychologist at the Monell Chemical Senses Center, in Philadelphia, told me. “We’re omnivores, and there is a lot of plasticity in the brain.” Taste begins as nature and ends as nurture.