Aldo González is a tall, square-shouldered Zapotec Indian of 45 whose long hair falls halfway down his back. He is one of 400,000 Zapotecs whose ancestors built Monte Albán, one of the greatest and earliest cities of Mesoamerica, and who have lived in this part of Oaxaca, high in the Sierra Juárez mountains, for thousands of years. The Zapotecs refer to themselves as the "people of the clouds," and most in the villages speak Zapotec. Virtually all land is held communally.

González studied electronic communication at a polytechnic university in Mexico City, but soon after receiving his degree he returned to Oaxaca, where he helps run the Unión de Organizaciones de la Sierra Juárez de Oaxaca (UNOSJO), a civil organization that represents Zapotec communities and their concerns. At the top of the list is corn, the farming of which is at the heart of Zapotec culture, as it is for all indigenous cultures in Mexico. But corn culture, and indigenous Mexicans, have been under siege ever since NAFTA went into effect in 1994 and the Mexican government concurrently initiated a number of measures designed to eliminate the country’s small-farm sector, which includes most indigenous corn farmers. The thinking behind the government’s decision was more economic than anti-indigenous—although it was arguably that too. Small farmers have long been the poorest of the poor in Mexico, and from the time of Mexico’s revolution they have received government subsidies. The government’s position on corn has been succinctly explained by Jorge Castañeda, former foreign minister under President Vicente Fox and now a professor at New York University (Fox was elected in 2000, six years after NAFTA). In his book Ex Mex (2007), Castañeda observes that it was "unclear…whether the rest of Mexican society should continue to subsidize 2.5 million families that will never escape from poverty growing corn on barren, rain-fed, tiny plots of land."

Like the Zapotecs, many of these farmers consider growing corn more than an economic activity. It is something closer to a defining way of life. Since NAFTA, to the surprise of government planners in Mexico City, many indigenous farmers, including the Zapotec members of UNOSJO, have in effect chosen to withdraw from the national economy, some weaning themselves off expensive chemical fertilizers and subsisting on the corn they can grow, harvest and barter. Economists refer to this phenomenon as a "retreat to subsistence," and life has not been easy for those who have stuck with farming. Poverty has descended upon the Mexican countryside and especially its indigenous areas, which are concentrated in Mexico’s south. In 2003 the World Bank reported that 40 percent of Mexicans lived in poverty but that in the heavily indigenous southern Mexican states of Oaxaca, Chiapas and Guerrero, 70 percent lived in "extreme poverty," a condition in which a population is unable to secure a daily minimum food requirement.

Despite those who continue farming, like Aldo González, many others have quit. By some estimates, dispossessed farmers account for almost half of the 500,000 or so Mexicans who, until the recent recession, immigrated illegally to the United States each year. González told me of whole villages where only the elderly remain.

Maize—"corn" in the vernacular—is, in the amount produced, the largest grain crop in the world. In most places it is grown as animal feed; but in Mexico, for reasons unique to the country’s culinary history, it provides some 70 percent of the caloric intake of rural families. Part of the process of making tortillas and tamales in Mexico is the pre-Columbian practice of lime cooking known as "nixtamalization," which increases the availability of calcium, amino acids and niacin in corn. Nixtamalization makes maize—especially when combined with beans—a complete protein. In the Popul Vuh, the ancient Maya book of origins, the first men are made of corn; part of the sway that corn holds over the region is that it evolved here. Archaeobotanists believe that some 9,000 years ago in the Rio Balsas valley in the Mexican state of Guerrero, early agriculturists began cultivating teosinte, a native grass, by carefully selecting for a series of mutations that included a sealed seed head and multiple rows of kernels attached to a central axis.

To this day, indigenous farmers continue to comb their fields for successful plants with useful characteristics, saving their seeds and exchanging them with neighbors. This process is central to indigenous culture in Mexico, and through continuous breeding indigenous agriculturists have internalized and accelerated the process of not just crop domestication but also plant evolution. In the Mexican countryside there are fifty-nine corn "landraces," distinct cultivars that have been carefully developed over millenniums by indigenous farmers for different attributes: growth at high altitudes, early or late maturation, the ability to withstand drought or heavy rain and utility for particular dishes or shamanic rituals.

Mexico’s landrace corn is consumed locally, but because it benefits from 9,000 years of breeding for diverse conditions, it represents a reservoir of genetic adaptability that many consider essential to the future of the world’s commercial corn crop. Kathleen McAfee, a political economist at San Francisco State University, observed that Mexican landraces "may even prove vital in the future to the continued productivity of corn farming worldwide, given that new traits must be continuously added to maize and other crops as crop pests evolve and climatic conditions change."

Landrace preservation, moreover, reflects a larger issue. Mexico has long been recognized as one of the world’s most biodiverse regions. Along its mountainous spine, the climate ranges from neotropical to Nearctic. Over time, as the earth has warmed and cooled, various plant communities migrating between North and South America have become isolated among Mexico’s deep valleys and high peaks, where they have evolved in exotic isolation. Indigenous cornfields in Mexico are known as milpas. Typically, milpas contain not just landrace corn but also squash, beans and other crops that farmers have coaxed out of their biodiverse surroundings through astute and assiduous husbandry. Because so many staple crops evolved in the region, it is considered a "center of origin" of crops, one of the few in the world.

What’s particularly notable about Mexican cornfields are the "weeds" that coexist with more established crops and, in many cases, have herbal and culinary uses. A 2004 report by the Commission for Environmental Cooperation (CEC), an environmental organization created by a side treaty of NAFTA, noted that "this group of species are not ‘weeds’" in the narrow American and European sense. "The relationships of Mexican poor peasants with their ‘weeds’ may be quite complex," and weeds "represent a rich genetic resource on which selection towards domestication may take place."

Aldo González and other indigenous farmers are well aware of their link to the ancient practice of plant domestication. One morning not long ago González and I walked into his milpa through stands of dahlias and wild salvia. In addition to showing me his two-month-old white corn and his snaky squash and bean vines, he pointed out a wild, self-sown tomato; an Amaranthus, a relative of the grain crop widely eaten by indigenous people in South America; and a traditional Zapotec medicinal herb used to coax out "malos aires." Around the edges of the field, González identified a wild avocado tree, a grove of guayabas and a huaje tree, an edible bean tree from whose name the city name of Oaxaca is derived. "The important thing," he told me, "is that we clean out and plant the fields but don’t break the connection to the surrounding ecosystem. These fields are part of the natural system; they’re not apart from it."

Inside Mexico, NAFTA was the project of a group widely referred to as "technocrats" in the government of Carlos Salinas de Gortari who belonged to the modernizing wing of Mexico’s ruling party, the Partido Revolucionario Institucional (PRI). When Salinas came into office in 1988, the government—as a legacy of Mexico’s revolution—was highly protectionist, strong on social services and involved in one way or another with just about every aspect of the economy. By the standards of modern free-market economies, Mexico was inefficient and often corrupt, and people were relatively poor, but the government’s social and economic benefits were widespread.

Salinas and his technocrats decided to slash the safety net and throw open Mexico to free trade. Salinas argued that Mexico’s low wages and physical proximity to the United States gave it a natural advantage as an exporter, and he promised to close the wage gap between the two countries by developing an export economy. He thereby aimed to solve the historic problem of immigration to the United States. Mexico, Salinas promised, would "export goods, not people."

For many Mexicans and non-Mexicans at the time, the prospect of change was welcome. According to Laura Carlsen, director of the Mexico City–based Americas Program of the Center for International Policy, "There was a feeling of euphoria. People were convinced [NAFTA] was going to create jobs, create industrial corridors, reduce emigration and get people out of rural areas where they didn’t have services. At that point, no one was talking about the ties of indigenous people to the land."

Part of the thinking behind NAFTA involved the doctrine of "comparative advantage," the idea that in global trade each country should take advantage of its natural strengths. Mexico’s advantage was its cheap and plentiful labor force; however, although corn had evolved in Mexico and has been grown there for thousands of years, the negotiators agreed that the United States had the comparative advantage in corn production. According to Michael Pollan in The Omnivore’s Dilemma (2006), because of hybrid corn and synthetic nitrogen fertilizer, the fruits of the "Green Revolution" of the 1950s and ’60s, the productivity of corn farms in the United States has increased from twenty bushels an acre in 1920 to as many as 200 now.

But Pollan and others have argued that comparisons of small-scale and industrial productivity can be deceptive. Each bushel of industrial corn in the United States requires between a quarter and a third of a gallon of oil for fuel, fertilizer and other applications. This can add up to fifty gallons or more of oil per acre, a level of consumption that is practicable only as long as fossil fuel is cheap. Heavy government subsidies paid to farmers, moreover, have also masked the real cost of corn. Pollan tells us that in Iowa, in 2005, it cost $2.50 to grow a bushel of corn that sold at the grain elevator for $1.45.

Industrial agriculture can also have steep "external costs." Timothy Wise, research director of the Global Development and Environment Institute at Tufts University, points out that corn is one of the most chemically dependent crops. Moreover, the prices at which it is sold fail to account for the associated environmental damage caused by chemicals. High on the list of damages is the growing "dead zone" at the mouth of the Mississippi River in the Gulf of Mexico; roughly the size of New Jersey, the area is almost devoid of marine life as a result of nitrogen runoff.

The NAFTA negotiators overlooked these concerns. Soon after NAFTA was signed, tariffs on corn from the United States were eliminated and US corn began flooding Mexico. Corn was further subsidized for export by the US government and arrived in Mexico at 20 percent below its already subsidized cost of production. Much of the corn from the United States was intended as animal feed, but it depressed the price of corn generally and by 2008 the real price paid to Mexican corn farmers had dropped 50 percent.

Simultaneously, within Mexico the government dismantled programs that had supported small farmers since the revolution. At the time NAFTA took effect, a government agency known as CONASUPO handled more than half of the nation’s corn crop; it administered price supports, offered storage infrastructure and assured minimum incomes through subsidies. By 1999 CONASUPO had been phased out, leaving Mexican farmers to their own devices; meanwhile, in the United States, the 1996 and 2002 farm bills approximately doubled agricultural subsidies.

Not everyone agreed with the NAFTA agricultural measures. Alejandro Nadal, a professor of economics at the Colegio de México, is critical of the government’s failure to think through the dismantling of "the most strategic sector of Mexico’s agricultural economy." As Nadal told me, "There were 3 million corn producers and five people per producer family. That’s 15 million people. Then there were transporters and other attached industries—22 million people—a quarter of the country’s population. Before putting the corn sector into NAFTA, wouldn’t you think about it twice? The government had no single study for why they put corn into NAFTA."

In an essay in Sin Maíz, no Hay País, a book on Mexico’s corn crisis published in 2003, David Barkin, a professor at the Autonomous Metropolitan University of Mexico, quotes a Salinas-era technocrat who says that it was the administration’s policy to remove half of the population from Mexico’s rural areas within five years. It’s unclear what the government ever had in mind for the displaced farmers. At the time, a political scientist who closely monitored Mexican politics told me, "They have no credible prediction as to where these people will be employed. My guess is that they’re thinking Los Angeles."

In general terms, the Salinas administration assumed NAFTA export industries would generate jobs for displaced farmers. It was soon proved wrong. According to NAFTA’s Promise and Reality, a well-regarded 2004 report from the Carnegie Endowment for International Peace, in the first decade of NAFTA a million workers a year entered the Mexican labor force, while the economy created only half a million jobs annually. Perhaps not coincidentally, the tide of immigration to the United States swelled during these years to about the same number—half a million a year.

In New York City I asked the Mexican economist Juan Carlos Moreno-Brid why the Mexican export-oriented economy had not been able to grow the way China’s export-oriented economy has. China, he explained, has followed an industrial policy that has created "linkages" requiring foreign investors to buy materials in China. The effect has been to spread around the export growth. NAFTA, by contrast, was deeply rooted in the philosophy of free trade (economists speak of it as one of the most extreme free-trade agreements ever negotiated) and specifically precluded any such arrangements. Mexico developed an export sector, Moreno-Brid told me, but it consisted largely of maquiladora plants assembling imported components. These plants generated relatively few, relatively low-paid jobs, and their influence has not spread into the larger economy.

There are, of course, other problems with NAFTA. The economist Thomas Palley refers to it as "a watershed in international agreements," a new type of treaty in which production floats between countries "always threatened by competition from poorer countries below." Palley’s point is well illustrated in Murder City, Charles Bowden’s chilling book about the border city of Juárez. Over the past decade, according to Bowden, approximately 100,000 jobs have left Juárez for China because China’s wages are only a quarter of the already punishingly low wages in Juárez. The main consequence of Juárez’s low wages and disappearing jobs is the drug business. "In Juárez," Bowden writes, "the payroll for the employees in the drug industry exceeds the payroll for all the factories in the city."

Genetically modified corn was first commercially planted in the United States in 1996. By 2000 it already accounted for 25 percent of the US crop, and according to The Impact of Genetically Engineered Crops on Farm Sustainability in the United States, a recently released report from the National Research Council, by 2009 it accounted for 85 percent. Virtually all genetically modified corn is of two technologically simple types: a corn implanted with a Bacillus thuringiensis (Bt) gene that imparts resistance to several insects; and another implanted with a gene that creates tolerance to glyphosate, an herbicide. The latter allows farmers to spray entire fields without damaging the crop. The National Research Council report points out that even though genetically modified corn seed costs considerably more, it saves farmers the costs of other, often more environmentally damaging pesticides and herbicides and the labor costs of applying them. "It’s a business model, really," a prominent biologist explained to me.

After harvest in the United States, genetically modified and non–genetically modified corn are freely mixed, and without elaborate testing it is impossible to tell the difference between them. At the time NAFTA was negotiated, genetically modified corn had not been an issue, but as corn from the United States began to inundate Mexico, the Mexican government became concerned that it could crossbreed with Mexican landraces, possibly leading to hybrids that could overrun native corn. In 1998 the government issued a moratorium on planting genetically modified corn. By then, however, the United States was shipping millions of tons of corn to Mexico, any single kernel of which could be genetically modified. The moratorium proved unenforceable. (It has recently been rescinded—although only in areas deemed not to be "centers of origin" of corn.)

Scientists with reservations about genetically engineered crops maintain that the ways in which transgenes—the packages of genetic material implanted in a host plant—interact with the genome of the host are little understood. Transgenes, they argue, are inserted into the host genome largely at random and could make their way to unintended parts of the host genome and switch on unintended genes. "We know very little about what happens after the transgenic insert," Paul Gepts, a professor of plant science at the University of California, Davis, told me.

A larger concern with genetically modified crops is spelled out in Environmental Effects of Transgenic Plants, a 2002 report from the National Research Council. It describes the tendency of introduced crops to hybridize with populations of their wild relatives. In a number of instances, this led to the creation of weedy hybrids that overran local wild populations and made them extinct, sometimes within a decade or less. The report refers to the field of "invasion biology" and notes that there’s more to learn about the reasons for different degrees of invasiveness. The tendency of hybrid species to invade populations of their wild relatives is well documented, however, and the report noted that there was no reason to believe transgenic plants would behave any differently.

These concerns had special resonance in Mexico. Corn cultivation here differs radically from that in the United States. In the United States, commercial corn is grown each year from new seeds. At the end of the year, whatever traits corn possesses—or may have picked up—disappear. In Mexico, by contrast, seed preservation and exchange is central to indigenous corn culture. Landrace corn, moreover, is "open pollinated": through the exchange of pollen, it can pick up and pass along whatever traits happen to be in adjacent plants—including genetically modified plants. If landrace corn happened to pick up genetically modified genes, those genes could be passed through seeds to subsequent generations.

In the United States, moreover, there are virtually no wild relatives of corn, and the possibility that transgenes might move from modified to wild corn plants has been little studied. Regulatory policies are based, as Kathleen McAfee puts it, on the idea that transgenes "will remain confined to the crop and the harvest cycle into which they were intentionally placed." In Mexico, by contrast, there are dozens of landrace corns with which genetically modified corn might interbreed. The Mexican government’s concern, therefore, was that if genetically modified genes were to get into landraces, not only would they not be removable but they could lead to their extinction.

In the late 1990s Zapotec farmers in Oaxaca began to notice what they thought were unusual numbers of mutant plants in their fields. Already inflamed by the government’s agricultural policies, the Zapotecs were deeply suspicious of genetically modified corn and approached two scientists then working in the area, Ignacio Chapela and David Quist of the University of California, Berkeley, and asked them to test the plants for evidence of transgenes.

In their lab, Chapela and Quist found not only evidence of transgenes but also, to their great surprise, what they considered to be clear evidence that the genetically modified genes had fragmented and become redistributed within the host plants. This seemed to fulfill the worst fears of those concerned about genetically modified crops: that implanted genes were unstable and could run wild inside related genomes. In November 2001 Chapela and Quist published their findings in Nature. Their paper caused an immediate uproar. Both scientists had been outspoken in their opposition to a recent funding agreement between their department and Novartis, whereby in exchange for millions of dollars the department had given the agro-biotech giant a significant stake in its research. Reactions to Chapela and Quist’s paper depended largely on how people felt about the Novartis controversy. Critics argued that the article’s evidence failed to support the authors’ second point—that genetically modified genes were unstable within the genomes of their host plants.

Under tremendous pressure, Nature published an unprecedented statement criticizing the evidence for this assertion. Chapela and Quist stood by their findings, and supporters of the two scientists argued that Nature‘s statement was inappropriate: the paper had been peer-reviewed; postpublication debates often discover weaknesses in published research, and the normal procedure would be a follow-up article. The controversy was unusually bitter and personal, and raged far beyond the pages of Nature. Eventually, the Guardian reported that among the most persistent of Chapela and Quist’s critics were a pair of fictitiously named web posters connected to a Washington PR firm hired by Monsanto, the world’s leading producer of genetically engineered seeds.

Chapela and Quist’s paper nevertheless generated further studies—some confirmed transgressed genes, but others did not. Most recently, a study by an international team led by Elena Alvarez-Buylla of the National Autonomous University of Mexico and published in the journal Molecular Ecology seems conclusively to support Chapela and Quist’s findings. Ultimately, the resolution of the issues raised by Chapela and Quist is less significant than the agitation their Nature paper caused in the Mexican countryside. In 2002, not long after the paper appeared, a group of Zapotec leaders from the municipality of Ixtlán de Juárez, supported by three Mexican environmental groups, filed a petition with the Commission for Environmental Cooperation to conduct a study of the implications of the genetically-modified-corn problem.

The CEC’s report, Maize and Biodiversity: The Effects of Transgenic Maize in Mexico, appeared in 2004 and consisted of a workmanlike summary volume and ten beautifully detailed background chapters—a number of which are almost novelistic in their complexity. The background chapters were written by leading biologists as well as experts on the politics and sociology of the Mexican countryside, and they examine the political, social and ecological value of indigenous cornfields and also the ways genetically modified genes might flow through those cornfields. Timothy Wise at Tufts told me that Maize and Biodiversity is "the best study of gene flow to date."

The CEC report argued that because the ecology of a traditional Mexican cornfield is so much more complicated than that of cornfields in the United States, studies conducted in the United States of the interaction between genetically modified corn and its surrounding environment were useless in Mexico. "Will the introduction of transgenic maize have a positive or negative effect on natural ecosystems in Mexico?" one of the CEC background chapters asked, concluding that "existing data on transgenic maize will not address the question sufficiently."

The report held that "the introgression of a few individual transgenes is unlikely to have any major biological effect on genetic diversity in maize landraces." But it went on to argue that not enough was known about the ways genetically modified plants would behave in the complex environment of a Mexican cornfield to rule out the possibility that an introgression of genetically modified genes would produce a weedy superhybrid that could overrun not just native landraces but also the wild teosinte grass that still grows around indigenous cornfields. One of the background chapters pointed out that such an outcome would be a "catastrophe" that could gravely reduce the genetic diversity of the world’s corn.

In the end, the authors of the CEC study unanimously agreed that until the effects of introgressed transgenes could be properly studied, all 6 million tons of US corn then entering Mexico each year should be ground at the border before being transported into the country. In doing so, the report’s authors evoked a regulatory category increasingly used in international environmental law and known as the "precautionary principle." The CEC’s authors argued that, given the possibility of irreversible damage to the heritage of corn in Mexico, the genetically modified corn industry bore the burden of proving its safety. This was significant for US agribusiness because the logic of the precautionary principle had once been used to bar US corn from the European Union.

The reaction in Washington was furious. Judith Ayres, a Bush appointee and the assistant administrator of the office of international activities for the Environmental Protection Agency, appended comments to the summary report. She attacked the degree to which it combined political and scientific issues and failed to consider the benefits of post-NAFTA agricultural developments—particularly to the growth of the Mexican livestock industry (a market for much imported corn). It ultimately lacked "policy relevance," Ayres declared. It was too late for the summary report to be withdrawn, but the ten background chapters that treated different aspects of the problem in such fascinating detail were never published and effectively suppressed. (They are nevertheless archived at www.cec.org/page.asp?PageID=924&ContentID=2796.)

The underlying worry of scientists concerned about Mexico’s landraces is the narrowness of the genetic base of commercial corn. As the effects of climate change become more pronounced, the corn belt in the United States will likely be affected not just by rising temperatures but also changing rainfall patterns. With these altered conditions will arrive plant diseases to which the corn crop has not previously been exposed. The devastation such diseases could wreak is hinted at by the effects of the Southern corn leaf blight in 1970. Before it was controlled, the blight destroyed 50 percent of the crop in some Southern states and 15 percent of the crop nationwide, and it caused $1 billion in damage.

I asked one of the CEC authors, Major Goodman, a professor of crop science at North Carolina State University and one of the nation’s leading corn experts, about the condition of commercial corn in the United States. He compared it with that of potatoes in Ireland before the potato famine and then continued, "We’re basically looking at the descendants of about seven inbred lines and the derivatives of those lines," he told me. "There are an awful lot of similar hybrids out there." Goodman is concerned about two diseases—one in Argentina and one in Africa. "Each is a virus spread by a leaf hopper" (a piercing insect that can spread plant diseases). "A leaf hopper could cling to a person’s luggage or clothing and jump on a plane without trouble. I’m 99 percent certain that not a hybrid on the market has resistance."

The genetic material that the corn industry would use to breed in resistance to such a virus would typically originate in a germplasm bank—a specialized facility that stores the genetic material needed to reproduce important crops (germplasm banks in Mexico contain samples of the seeds of the nation’s landrace corn). But as Goodman put it, "If we are to have climate change, it will be hard to meet the problems it presents out of a germplasm bank. Basically, germplasm banks deal in hundreds of kernels. The only way to make them available, in the case of rampant plant disease, would be to grow them out seed by seed."

Monsanto has recently said that it is working to address climate change and has promised to create crops that will require 30 percent less water, land and energy to grow. Specifically, it promises to develop a "drought gene" designed to dramatically reduce a plant’s water consumption. Monsanto’s drought-resistance work is widely believed to involve "transcription factors," types of master genes that regulate numerous other genes.

Industry critics are skeptical of Monsanto’s claims. Goodman explained to me that to date there were essentially only two commercial gene-implant applications—Bt crops and glyphosate-resistant crops—and that each was the result of single-gene engineering. "Drought tolerance is a genetically complex trait," he said, and the present state of genetic modification is confined to implanting "single genes affecting single traits." Paul Gepts agreed with Goodman’s point that drought resistance was a genetically complex trait and added that it would require an ability to engineer sequences of genes that had not yet been attained. "They may have something," he said, "but I’m skeptical. They have to please their stockholders. They have to attract capital."

Last year the Union of Concerned Scientists released Failure to Yield: Evaluating the Performance of Genetically Engineered Crops, a report that surveyed applications to the Agriculture Department seeking permission for field trials of new types of transgenes. (Applications for the tests are public; the test results are confidential.) The report found that, from among thousands of applications, none beyond implants of single genes with Bt or with glyphosate resistance had resulted in commercially successful products (the report excluded a small number of virus-resistant traits). Failure to Yield attributed this state of affairs to the complexity of the roles played by the genes being experimented with (including transcription factors) and described these genes as being "parts of genetic networks that have multiple and far-reaching effects on the growth or development of the plant." Unlike the single-gene products now on the market, the report noted, the multiple-gene applications had greater potential for "deleterious unintended side effects."

Farmers have recently faced other problems with genetically modified crops. The seed industry has become concentrated in very few hands, and prices have soared. In the meantime, a number of weeds that had, until recently, been killed by glyphosate have evolved glyphosate resistance with alarming speed, requiring farmers to revert to older herbicides and dampening the appeal of the expensive modified seeds. One Iowa State weed scientist described the situation to the New York Times as "Darwinian evolution in fast forward."

Failure to Yield also looked at crop yield and concluded that genetically modified crops had done substantially less to increase yield than a number of more conventional measures, ranging from organic farming to a technologically sophisticated form of genetic breeding known as "marker-assisted selection." This has not led anyone to conclude that the engineering of transcription factors or other such complex multigene undertakings are unattainable but, rather, that their imminence may be overstated. "Eventually we will be able to engineer more than a single gene," Goodman says, "but there are complications, and it will take a hell of a long time to work them out."

This raises a question. Gepts had explained to me that many of the traits found in landrace corn are located in complex "suites" of genes. These traits include such properties as flowering time, crop yield and drought resistance. Considering that the multiple attributes of landrace corn are themselves the product of a sophisticated, longstanding tradition of crop breeding, would it be fair to think of landrace corn as having already achieved, on some level, the very properties that genetic-engineering firms were spending hundreds of millions of dollars to try to breed into commercial corn? If so, how had peasant farmers done this?

"In indigenous fields," Gepts told me, "these suites result from both environmental pressures and from farmer selection—probably more from the latter. These suites contain traits that have been selected by farmers over time," he said, "farmers with a very keen understanding of plants."

After leaving Aldo González’s milpa I traveled west into the high, dissected plateau that is the home of the Mixtecs, Oaxaca’s second-largest indigenous group. I had arranged to meet Jesús León Santos, the head of a Mixtec organization known as CEDICAM, which works to support traditional Mixtec agriculture. In recognition of CEDICAM’s efforts, Jesús León had won a prize not long before from the Goldman Environmental Foundation in San Francisco.

Jesús León met me in his battered pickup truck outside the Mixtec town of Nochixtlán. As we drove, he recited a maxim of his father’s: "Plant to eat first or you’ll wind up working for others." He spoke of pressure from the government to persuade Mixtecs to plant hybrids, abandon their traditional landraces and use chemical fertilizers. He recounted the post-NAFTA decline in prices paid for corn and the simultaneous sharp rise in the price of fertilizers. ("Fertilizers damage the land, but the biggest damage is to the people, because they lose the ability to live off the land," he said.) He described government policies of descampesinoización—getting rid of small farmers—and of efforts to turn farmers into manos de obra, workers for factories and maquiladoras. He reflected on the toll of emigration: how it was mostly men who left and that husbandless households damaged the transmission of values between generations ("It will have an effect in the future").

Eventually, we arrived at Jesús León’s milpa. He pointed out the landrace corn, squash, beans, a wild potato and various quelites—a Nahuatl word that has become a generic indigenous term for usable milpa weeds. I asked Jesús León about the ways milpa agriculture seemed to be about improving on nature, on natural processes.

He stopped—with the whole vulnerable world of traditional human agriculture around his feet. "No," he said, and seemed to care deeply that I follow precisely what he was saying. "It’s not a way of improving nature—it’s a way of getting closer to the processes of nature, getting as close as possible to what nature does."