Free Tasty by John McQuaid

bitter things as long as I’ve been an adult. Non-tasters tend to be insensitive to other flavors, too, one possible explanation for why I like spicy food, and have trouble telling fine wines apart.
    Then I took a leap forward into the twenty-first century. My family and I spit into tiny plastic test tubes, sealed them up, and sent them to the genetic testing service 23andMe in Mountain View, California, named for the twenty-three pairs of human chromosomes. The company’s genetic profiling technology traces your place in the human family: the continents your ancestors came from, your risk for possible diseases with genetic components, the amount of Neanderthal DNA you carry thanks to ancient inbreeding. The test also reveals which type of Arthur Fox’s bitter gene you have. After a few weeks, I got the results from the company website. All of uswere non-tasters. This meant both my wife and I had inherited two copies of a particular non-tasting variant of the gene from our parents, and then passed these on to our kids. (The tests also showed 3 percent of our genome was Neanderthal; about average.) This fit my son’s profile, with his penchant for spicy foods. But it seemed to contradict my daughter’s preference for bland ones.
    Between Fox’s time and ours, the human genome—all its genetic material—has been discovered, unspooled, recorded, and partially decoded. Person to person, our genetic code differs on the order of only a tenth of a percent. But that small amount accounts for vast differences in body type, skin color, disease risks—and taste.
    In the 1930s no one knew what a taste gene looked like, how it worked, or how the tongue or the brain could distinguish bitter from sweet. There were tantalizing hints about what occurred in these strange domains, but they were nearly impossible to detect with the scientific tools of the time: too small for a microscope, yet larger and more complicated than the chemist’s traditional bailiwick of molecular reactions in test tubes. One scientist called it “the world of neglected dimensions.”
    By the 1960s, Massachusetts Institute of Technology molecular biologist Martin Rodbell was able to describe the strange biology of taste and genes using the lingo of the then-dawning digital age. Cells, he suggested, respond to their surroundings like a computer handles inputs and outputs. Something called a receptor was in charge of input: it sensed certain things such as bitter molecules, or hormones. Like flipping a switch, this triggered an electrical reaction inside the cell that beamed out a message across the nervesand to the brain, or another part of the body. Rodbell called this switch the “transducer.” Taste, in other words, could be understood as a simple form of computing. A braised steak, a cup of coffee, a bitter berry—all contain thousands of different substances. Taste receptors—each made by a taste gene—extract essential information out of the chemical chaos of lunch and turn it into a code that the brain can interpret, so it can then react.
    The anatomy of taste is a testament to just how wrong the original tongue map was. The average human tongue contains about ten thousand taste buds—tiny structures found on the visible, nub-like papillae. During a meal, the mix of food and drink in the mouth enters a bud via a single, pore-like opening at its tip. A bud is a knotted clump of fifty to eighty specialized cells, each detecting one of the basic tastes. One part of a coiled receptor protein protrudes out of a cell, the other part sits inside. The outside strand grabs molecules floating by, forming a temporary chemical bond. This makes the loops inside the cell pull apart, like the stems at the bottom of a bouquet when the middle is grasped too tight. This signal, essentially flipping the nerve cell to “on,” triggers the cascade of signaling from the tongue to the brain that culminates, a