It's an hour-and-a-half drive over switchbacks from the southern Mexican city of Oaxaca to the village of Capulalpan, a settlement of some 1,500 people nestled in the Sierra Norte Mountains. The thick forest and remoteness of this mountainous region has long enabled the local Zacateca Indians to maintain their cultural integrity and, to a great extent, write their own rules. When Mexican clocks were turned back for daylight saving time in the spring, the Zacatecans refused to make the adjustment, insisting that they live in "God's time," not in what they derisively call "Fox time," referring to President Vicente Fox in far-off Mexico City. Carlos Castaneda wrote about this region as a center for natural transcendence in his book Journey to Ixtlan. But over the past year, this tiny puebla among the cedars and the wild mustard of the Sierra Norte has been unwillingly thrust into the center of a worldwide controversy over something quite different than the quality of its peyote: genetically engineered corn.

Last winter a team of plant scientists from the University of California, Berkeley, published a paper in the journal Nature asserting that the genes from genetically altered corn had been discovered in the local varieties of corn grown here in Capulalpan. The news traveled quickly. The biotechnology industry has long claimed that genetic engineering is predictable: that the genes end up where they are put, and that their presence in the environment can be controlled. But the discovery of genetically engineered (GE) corn in Capulalpan appeared to defy those claims. In 1998 the Mexican government outlawed the planting--although not the eating- -of GE corn, in order to protect the genetic diversity of the crop that is the country's most important food supply.

Preserving the rich genetic diversity of Capulalpan's corn is a matter of more than sentimental significance. When disaster strikes corn anywhere in the world--disease, too much rain, not enough rain, a new pest--plant scientists traditionally come to this region, which stretches from the Sierra Norte Mountains down to the southernmost state of Chiapas and into Guatemala, for the germ plasm to rejuvenate beleaguered domestic varieties. Genetic diversity is what provides a hedge against unanticipated environmental changes. In the state of Oaxaca alone, corn grows in sixty different varieties, in shades of blue, black, purple and white, as well as the yellow that we have come to associate with our most widely grown crop.

"This is the world's insurance policy," says Mauricio Bellon, director of the economics programs at the International Maize and Wheat Improvement Center (CIMMYT), the world's foremost public research facility for corn. "The diversity of these land races, these genes, is the basis of our food supply. We'll have great science, we'll have great breeding, but at the end of the day, the base [of this crop] is here. We need this diversity to cope with the unpredictable.... The climate changes, new plant diseases and pests continue to evolve. Diseases we thought we had controlled come back. We don't know what's going to happen in the future, and so we need to keep our options open. And this," says Bellon, in the middle of a Oaxacan cornfield, "is what keeps our options open."

The villagers in Capulalpan had no idea what genetic engineering was until they found the errant genes in their fields. Genetic engineering involves introducing genes from a separate organism into corn--or any of a number of other food crops--in order to express a desired trait. Olga Maldonado, the first villager in Capulalpan to discover transgenic elements in her corn, found the very concept bewildering. "Maybe it comes from some other plant," she said, "or animal--it has another ingredient that's different from corn."

Americans, too, might be blindsided by such a revelation, even though most of us eat genetically engineered products practically every day. Walk through your local supermarket, and you'll find it in breakfast cereals, canned drinks, processed foods of every sort. Unless it's duly labeled, chances are anything with processed soy or corn has been genetically modified. The most popular sweetener today is not sugar, but corn syrup--and most corn syrup is made from genetically modified corn. GE corn and soybeans are fed to animals, so it's in our beef, our pork, our chicken and our milk. Over the past five years, the products of genetic engineering have slipped almost unnoticed into the American food system. Though there is no hard evidence that these products are harmful to human health, foreign and domestic scientists and activists are questioning their long-term impact on the environment, whether their much-heralded benefits are actually coming true and whether the introduction of what is, in essence, a new living organism into the ecosystem can be so easily controlled. And now here these organisms were in Mexico--which had banned the planting of genetically engineered crops four years ago. If the genetic traces could make their way all the way to tiny Capulalpan, where else are they going to go?