Seated in the bed of a pickup truck, Joshua Tewksbury cringes with every curve and pothole as we bounce along the edge of Amboró National Park in central Bolivia. After 2,000 miles on some of the worst roads in South America, the truck's suspension is failing. In the past hour, two leaf springs—metal bands that prevent the axle from crashing into the wheel well—jangled onto the road behind us. At any moment, Tewksbury's extraordinary hunting expedition could come to an abrupt end.
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A wiry 40-year-old ecologist at the University of Washington, Tewksbury is risking his sacroiliac in this fly-infested forest looking for a wild chili with a juicy red berry and a tiny flower: Capsicum minutiflorum. He hopes it'll help answer the hottest question in botany: Why are chilies spicy?
Bolivia is believed to be the chili's motherland, home to dozens of wild species that may be the ancestors of all the world's chili varieties—from the mild bell pepper to the medium jalapeño to the rough-skinned naga jolokia, the hottest pepper ever tested. The heat-generating compound in chilies, capsaicin, has long been known to affect taste buds, nerve cells and nasal membranes (it puts the sting in pepper spray). But its function in wild chili plants has been mysterious.
Which is why Tewksbury and his colleagues have made multiple trips to Bolivia over the past four years. They're most interested in mild chilies, especially those growing near hot ones of the same species—the idea being that a wild chili lacking capsaicin might serve as a kind of exception that proves the rule, betraying the secret purpose of this curiously beloved spice.
Bounding along in the truck, we reach a cluster of houses next to a river. Somewhere near this spot a few years ago, Michael Nee of the New York Botanical Garden collected a C. minutiflorum specimen, and Tewksbury wants to sample its relatives. In his notes, Nee wrote that the fruit he tasted was sweet. But Tewksbury just encountered the same species several hundred miles away and tasted it himself. That one was spicy, and the discrepancy was worth investigating.
Tewksbury pops a wad of coca leaves—the source of cocaine and Bolivia's answer to espresso—into his mouth and steps smiling into the drizzling rain. A middle-aged man appears outside a low-slung house, his tan shirt open to his belt. Tewksbury says one benefit of his research is he doesn't have to look too hard for his subject. He just asks the local residents, tossing out a few Bolivian names for wild chilies: Any ulupica? Any arivivi?
The man shakes his head at the crazy gringo. Here? No. Up the mountain. Tewksbury is puzzled. "Are there any peppers without the spice?" he asks in broken Spanish. No, the man says. Tewksbury shrugs and crosses the highway to another yard, where a woman stands with a mop. She, too, says he must be mistaken. There's no ulupica here.
The other four people in our group linger at the vehicle. We're wet. Biting flies leave red welts on our necks and arms. Noelle Machnicki, a University of Washington graduate student, has a plane to catch. Tewksbury marches down the road, hops over a strand of barbed wire, and lumbers up a slope through a tangle of moist weeds. The others make halfhearted efforts to scan the area around the truck, while I follow Tewksbury up the hill. As he enters the forest, marble-size red globes catch his eye: C. minutiflorum. Tewksbury bites into a fruit. "Not pungent," he says, slipping a few into an envelope.
He walks over to another plant. It, too, is sweet. Soon he has tasted fruits from eight plants and not one is spicy. This could well be an entirely mild wild chili population—the first ever—he muses, then erupts into a frenzy of free association, cooking up evolutionary trees for the strange chilies. Suddenly, a monkey in the canopy above us leaps from one branch to the next, and rainwater cascades onto our heads. Tewksbury watches the animal's acrobatics before performing some of his own: a vine snags his ankle and he tumbles face first into a chili bush, another C. minutiflorum. Dazed, he plucks a fruit and bites into it. He spits it out and grimaces—this one is hot. He couldn't be happier.
People have been spicing up their food with chilies for at least 8,000 years. At first they used wild chilies, likely adding them to potatoes, grain and corn, says Linda Perry, an archaeobotanist at Smithsonian's National Museum of Natural History. She has found traces of chilies on ancient milling stones and cooking pots from the Bahamas to southern Peru. Based on her studies of potsherds from different archaeological sites, she concludes that people in the Americas began cultivating chilies more than 6,000 years ago. Just why they did is a matter of scholarly debate. Perry believes it was a question of taste. "Chilies were domesticated early and spread very quickly just because people like them," she says. "Do you want a big pot of yams or a pot of yams with chilies thrown in?" Other researchers, such as Jennifer Billing and Paul Sherman at Cornell University, argue that people learned early on that chilies could reduce food spoilage. And some scholars point to medical uses. Ancient Mayans incorporated chilies into medicinal preparations for treating infected wounds, gastrointestinal problems and earaches. Laboratory studies have shown that chili pepper extracts inhibit a number of microbial pathogens, and capsaicin has been used in a local anesthetic.