David Quist found more than he was looking for. Two autumns ago, the UC Berkeley graduate student was working in Sierra Norte de Oaxaca in southern Mexico, preparing to lead a workshop for local farmers who had set up an agricultural science lab. The next day's lesson was on a technique to test seeds for evidence of genetic modification. For the exercise, workshop attendees were going to test corn purchased from the local government food store, much of which comes from the United States in this post-NAFTA age. To show his students what a positive signal would look like, Quist had brought along some transgenic corn DNA from the United States, where about forty percent of the crop is now genetically modified. To demonstrate a negative signal, he planned to use native corn, or criollo, grown in Oaxaca, the evolutionary cradle of the species. But while prepping for the workshop, Quist kept getting an alarming result: His negative control was testing positive. The native corn, it seemed, showed evidence of genetic modification.
What Quist saw was either inevitable or horrific, depending on whom you ask. Oaxaca is the center of genetic diversity for maize, and diversity is essential to the survival of a species. It's what keeps entire populations from being wiped out by a single blight, pest, or change in climate. But human tinkering has led to some unfavorable trends; 75 percent of the planet's natural genetic crop diversity has been lost over the last century, according to the UN Food and Agriculture Organization. Much of that loss has been attributed to the commercialization and globalization of agriculture. Transgenic crops -- those bearing genes from other species -- are considered a particular threat to diversity because they are engineered for survival, with special traits such as resistance to insects, chemical sprays, or harsh environmental conditions like salinity or drought. Bioengineering's critics say these very advantages could allow transgenic plants to take over and further homogenize the gene pool.
For Mexico, this is of particular concern. The Mexican government outlawed the planting of transgenic maize in 1998 to protect its national crop from cross-pollination, though it allows import of the gene-altered product as food and animal feed. Despite such regulations, environmentalists worry that modified crops could end up dominating the gene pool anyway, especially with a promiscuous, wind-pollinated species such as corn. Evidence of cross-pollination in remote Oaxaca did not augur well for the government's ability to keep transgenes out, and Quist says he fervently hoped what he was seeing was a false positive.
Quist's advisor, microbial ecologist and UC Berkeley associate professor Ignacio Chapela, suggested that he return home to retest his samples. Back in the team's laboratory at the university's Department of Environmental Science, Policy, and Management, the young researcher ran the maize through several more rounds of experimentation. While tests on two of the samples were negative, four of the six native corn samples indicated the presence of transgenes. Quist also tested a sample from the government food store, which came back strongly positive.
Specifically, Quist was finding a gene fragment from the cauliflower mosaic virus that is often used to boost the expression of newly introduced genes in engineered crops. He also believed he'd found other small DNA fragments common to transgenic crops, and evidence of a diversity of sequences flanking the viral DNA, which led him to conclude that the foreign genetic material had moved around to different parts of the genome, and was being passed from one generation of plants to the next via pollination. Quist and Chapela estimated that, based on their data, one to ten percent of native Mexican maize might be similarly affected.
If correct, the team's conclusions could have profound ecological and political implications. Critics of genetic engineering warn that the invasion of transgenes into native varieties could provoke a host of negative effects: Such a crossover, they say, could create new allergens in food and further shrink agricultural gene pools, leaving whole crop populations vulnerable to destruction -- as occurred in the disastrous Irish potato famine of 1845-1851, during which an estimated 1.5 million people starved to death. Furthermore, they say, poor farmers could become even more dependent on multinational corporations for their seeds. In the case of maize, it's feared that transgenic pollen could mingle with corn's inedible Mexican ancestor, teosinte, turning it into a "superweed." Finding transgenic DNA in the hills of Oaxaca, which were supposedly a bastion of genetic purity, suggested to Quist that cross-pollination might be far worse in the valleys, where the country's industrial maize production is based.
The discovery that transgene fragments seemed to be appearing at different locations within the genome was perhaps even more significant. It undercut the very premise that genetic engineering is a safe and exact science, that once new DNA is introduced into a species, humans can know and control exactly where the gene goes, how it will be expressed, and if it will be passed on to other plants.
The researchers knew their claims would be scrutinized closely when they published their results in the British journal Nature last November. After all, Quist says, the peer-review process had consisted of four rigorous reviews over an eight-month period by a team of anonymous experts. But no one could have predicted the magnitude of the controversy to come.
Over the past seven months, publication of the team's results has led to what some now call the "Mexican maize scandal." It has prompted Greenpeace to call for an investigation by the international Commission for Environmental Cooperation set up under NAFTA. It has left the Mexican government scrambling to confirm or deny the conclusions, and forced a prominent Mexico-based research center to defend the integrity of its gene bank. And it has fomented a contentious battle between prominent scientists and environmentalists, between those who would dismiss the study as junk science or defend Quist and Chapela as public-interest researchers victimized by an industry-led smear campaign to discredit them.
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