Travelers come to the city of Trujillo in northwestern Peru for its elegant plazas, unsullied colonial architecture, nearby archaeological riches and even the ultrafresh local catch of its ceviche restaurants. I, however, journeyed to Trujillo in search of a sprawling, scraggly vine.

It is known to botanists as Solanum pimpinellifolium, or simply “pimp.” The plant is the wild ancestor of all the tomatoes we eat today, and still grows wild in northern Peru and southern Ecuador. And although you may never have occasion to nibble one of its tiny red fruits, no bigger than a shelled pea, you owe this humble, untamed species a debt of gratitude every time you enjoy a spicy red sauce or slurp the sweettart juices of a summer beefsteak from the garden. “If it wasn’t for the genes of these wild species, you wouldn’t be able to grow tomatoes in a lot of areas,” Roger Chetelat, a renowned tomato expert at the University of California, Davis, told me before my trip to Trujillo.

Although you’d never know it from the colorful cornucopia on display at any farmers’ market on a summer Saturday, all modern domestic tomatoes (known botanically as Solanum lycopersicum) are remarkably similar. Taken together, they possess no more than 5 percent of the total genetic variation present within the wild species and primitive varieties. The domestic tomato’s progenitor has the other 95 or more percent. Modern tomatoes may taste good and offer eye appeal, but they lack many genes that allow them to fight disease and survive drought.

By contrast, the pimps and about a dozen other tomato relatives that grow wild in western South America are a tough crew, adapted to survive without the help of farmers in dramatically different climates: from some of the driest, harshest desert landscapes in the world to humid, rain forest lowlands to chilly alpine slopes. As far as we know, the inhabitants of the region never domesticated them. But a thousand miles to the north, the pre-Columbian residents of what is now southern Mexico set about planting and cultivating them, saving the seeds of those that bore the biggest, tastiest fruits and crossing desirable plants with one another. Distance prevented these early farmers from crossbreeding their new varieties with the original populations.

Domesticated tomatoes may have been more palatable, but they lacked the tenacity of the ones left behind in South America. And they grew more inbred when Spanish explorers brought a few seeds from present-day Mexico to Europe, further separating tomatoes from their ancestral roots. The tomatoes grown today in the United States and elsewhere are offspring of those European strains.

Beginning in the 1940s and 1950s, botanists started correcting this problem by crossbreeding the tough untamed species with domesticated cultivars to give them the immunity and vigor of their wild relatives. Pimps alone supplied genetic traits that allow tomatoes to resist devastating fungal diseases such as late blight, verticillium wilt and fusarium wilt.

Researchers found the wild tomatoes to be so valuable that they launched expeditions to western South America to collect seeds and preserve them in climate-controlled repositories such as UC Davis’s C. M. Rick Tomato Genetics Resource Center, which Chetelat heads. The center acts like a bank, sharing its more than 3,800 specimens with breeders and scholars around the world. Like any bank, it needs a steady stream of new deposits to continue operating, and those new deposits have to come from the wild. Over the past few decades, it’s grown harder to find them. According to Chetelat, there are

two main reasons.

One was evident after my driver, Carlos Chávez, left the outskirts of Trujillo and drove north along the Pan American Highway, here a straight ribbon of blacktop that bisects a desert that makes Arizona’s desert look positively lush. We drove for miles without seeing any sign of life—not a tree, shrub, blade of grass, nor even a cactus—on the sandy plain that spread out from the dun-colored peaks of the Andes on one side to a dark gray curtain of fog demarking the cold waters of the Pacific on the other.

We careered through a small town whose single dusty street was congested with moto-taxis, rickety conveyances that look like the offspring of a tryst between a motor scooter and a pedicab. On the far side of town, what had been nothing but unbroken sand became a horizon-to-horizon sea of sugarcane occupying every precious inch of the irrigated fields, right up to the highway’s edge. Chetelat had told me that pimps once thrived along the area’s fencerows, roadsides and ditch banks, but that intensive agricultural production had destroyed their habitat. Any wild tomatoes that managed to find a nook into which to sink their roots, he said, have been killed by herbicides sprayed over the sugarcane fields to kill weeds.

When I told Chávez that Chetelat had given me GPS coordinates for a clump of pimps he’d found on a field trip a few years earlier up in the mountains away from the cane fields, the driver shook his head. He told me that what the locals called tomatillos silvestres (little wild tomatoes) used to grow in the area. He remembered picking them and snacking on them as a boy during visits to his grandparents’ small farm on the outskirts of Trujillo. But it had been years since he’d seen one. “They are all gone,” he said.

The second problem facing scientists such as Chetelat is purely political. Beginning in 1992, members of the United Nations approved a treaty called the Convention on Biological Diversity. It established international regulations on the exploitation of genetic resources, including seeds and plants. If researchers from one nation want to use biological resources from another nation, they must first get its consent and fully inform the donor country about what they plan to do with the material. A corporation or university that profits from use of the biological resources must share the money equitably with the country of origin.

Every single member of the UN but one ratified the treaty, the notable exception being the United States. “Before, you could just take the seeds out of the country and distribute them to researchers and breeders,” Chetelat said. “Now you need prior consent to go in and collect. Then you need a separate

permit to export the seeds out of the country. Finally, you have to negotiate an agreement about how you would share any benefits that arise from any seed distribution. It has been impossible to negotiate such agreements with Peru.” Chetelat said he wouldn’t be as concerned if the government of Peru or university scientists there were actively collecting and properly storing wild tomato seeds, similar to the way the country has assembled native potato varieties at its International Potato Center. But Chetelat said that is not being done.

In the meantime, industrial agriculture continues to overtake former pimp habitat. Chetelat is particularly troubled about northern Peru, the area where pimpinellifolium populations are at their most diverse. “With the agricultural development, we’ve already lost populations we wanted to collect. And the worst thing is that we really don’t know what we are losing,” he said.

It was beginning to look as if my quest for pimps was going to be literally fruitless. Chávez and I turned up a narrow secondary road. The flat alluvial plain at the base of the mountains was an oasis crowded with small vegetable farms—corn, potatoes, rice, squash, leafy greens, domestic tomatoes—crosshatched by irrigation canals that channeled glacial runoff from a small river to the thirsty crops. The system has been in place in the area for at least 5,400 years.

After a few miles, the farms disappeared, and the road wound upward through a craggy landscape of sheer cliffs and precipitous valleys. Peruvian highway engineers apparently don’t see the value of guardrails, much to my sweatypalmed terror. But because there were no farms or sugarcane plantations, pimps at least had a chance of finding a spot where they could grow. Just outside Tembladera, a village wedged between the mountains and the turquoise waters of a reservoir, we stopped where my GPS indicated there should have been “a pretty good cluster,” according to field notes Chetelat had scribbled during his earlier expedition. A pretty good cluster of boulders, I thought, seeing no greenery whatsoever. Chávez approached three women who were walking up from town carrying grocery bags. They had a quick exchange that included a lot of head shaking. He came back to the car with the bad news I’d expected: no tomatillos silvestres.

We executed a U-turn and began retracing our route out of the mountains. We’d barely gotten rolling when I caught a flash of yellow out of the corner of my eye. “Stop,” I said, scrambling to get out of the car. There, growing out of a crevice in the rock ledge, was a familiar-looking, jagged-leafed vine spangled with miniature versions of the tomato flowers that bloom during the summer in my garden. Chávez was delighted and began pawing at the vine, stuffing any red berries he encountered into his mouth and repeating, “Tomatillos silvestres, tomatillos silvestres.”

I plucked a red berry, rolled it between my thumb and index finger and tasted. Sure enough, the pimp had the bright, sweet-tart pop of a tomato, but you’d have to pick for hours to get enough to make a salad. Its size belied its botanical importance. Perhaps this one pimpinellifolium, still stubbornly alive on a rock, was a sign of hope. But without the scientific and political will to harness the genetic power of the wild Peruvian tomato, it could just as easily be a sign of impending doom. In the coming decades, domestic tomatoes will doubtless face drought, new diseases, environmental destruction and climate change. To survive, they will need all the genetic resources they can get.