The Year In Ideas: A to Z; Genetic Pollution

The way we think about and deal with pollution has always been governed by the straightforward rules of chemistry. You clean the stuff up or let it fade with time. But what do you do about a form of pollution that behaves instead according to the rules of biology? Such a pollutant would have the ability to copy itself over and over again, so that its impact on the environment would increase with time rather than diminish. Now you’re talking about a problem with, quite literally, a life of its own.

This year, the idea of genetic pollution—the idea, that is, that the genes of genetically modified organisms might end up in places we didn’t want them to go—became a reality. In September the Mexican government announced that genes engineered into corn had somehow found their way into ancient maize varieties grown there—this despite the fact that genetically modified corn seed has not been approved for sale in Mexico. The country where corn was probably first domesticated, Mexico is today the source of the crop’s greatest genetic diversity. Now that diversity could well be threatened.

Companies like Monsanto have long acknowledged that their engineered genes (“transgenes”) might on rare occasions “flow” by means of cross-pollination from one of their crops into neighboring plants. But because sex in nature takes place only between closely related species, and because most crop plants don’t have close relatives in North America, the risk that new genetic traits would contaminate the genome of the world’s important crops was, the companies claimed, remote. As long as genetically modified corn seed wasn’t sold to Mexican farmers, or potato seed to Peruvians, these crucial “centers of diversity” could be protected.

So how did transgenes ever find their way into traditional Mexican corn varieties? It’s a mystery, but the leading theory is that some campesinos in remote mountainous fields outside Oaxaca bought some genetically modified corn as food—then planted the kernels as seed. No matter how it happened, Monsanto’s genes have spread widely in the region.

Why does this matter? The presence of transgenes in what some experts call “the cradle of corn” represents a threat to the crop’s biodiversity. Should the traits introduced into Mexican fields confer an evolutionary advantage (for insect resistance, say) on certain plants, their offspring could crowd out older varieties, leading to the extinction of genes we may someday need. For whenever a food crop suffers a catastrophic failure—as when blights destroyed the potato crop in Ireland in the 1840′s—breeders return to that crop’s center of diversity to find genes for resistance. Next time around, those genes may be nowhere to be found, a casualty of genetic pollution.

Greenpeace has called on the Mexican government to halt imports of genetically modified corn, but the genie is already out of the bottle. Genes released into the environment can replicate themselves ad infinitum. Indeed, some studies suggest that transgenes are particularly “sticky”—better at getting themselves around in nature than ordinary genes, possibly because of the viral and bacterial vectors used to engineer them. So far that’s just a hypothesis; we don’t really know how transgenes will behave once they’ve found their way into a crop’s center of diversity. What we do know, now, is that we’re about to find out.