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By Root 1330 0

far too little to wipe out vitamin A deficiency. In 2005, four years after Potrykus accused his critics of mass murder, Syngenta scientists discovered that adding an extra gene from corn helped boost the level of the vitamin A precursor more than twentyfold. It was a huge increase, but there’s no solid evidence yet of how much benefit it brings to people who eat it. Some nutritionists have warned that it may not bring much benefit at all, because vitamin A has to be consumed along with dietary fat in order to be properly absorbed by the body. It’s possible to suffer vitamin A deficiency—even to go blind—on a diet that contains vitamin A. Foods such as milk, eggs, and many vegetables offer the right combination of vitamin A and fat, but rice does not. Just because Golden Rice is at the cutting edge of genetic engineering doesn’t mean that it will cut down vitamin A deficiency any more than conventional methods have.

Using words like salvation to describe transgenic crops makes as little sense as calling them Frankenfoods. We are thrown back and forth between the extremes of abject terror and hope for miracles of loaves and transgenic fish. Genetically modified crops are hardly miraculous. They are living things, as much subject to the rules of life as E. coli or humans. And just as E. coli has evolved defenses against some of our best antibiotics, natural selection is undermining the worth of the most popular transgenic crops.

About 80 percent of all the transgenic crops planted in 2006 were engineered for the same purpose: to be resistant to a herbicide known as glyphosate. Glyphosate kills plants by blocking the construction of amino acids that are essential to their survival. It attacks enzymes that only plants use, with the result that it’s harmless to people, insects, and other animals. And unlike other herbicides that wind up in groundwater, glyphosate stays where it’s sprayed, degrading within weeks. A scientist at the Monsanto Company discovered glyphosate in 1970, and the company began selling it as Roundup in 1974. In 1986, scientists engineered glyphosate-resistant plants by inserting genes from bacteria that could produce amino acids even after a plant was sprayed with herbicides. In the 1990s, Monsanto and other companies began to sell glyphosate-resistant corn, cotton, sugar beets, and many other crops. Instead of applying a lot of different herbicides, farmers found they could hit their fields with a modest dose of glyphosate alone, which wiped out weeds without harming their crops. Studies indicated that farmers who grew the transgenic crops used fewer herbicides than those who grew nontransgenic plants—77 percent fewer in Mexico, for example—while getting a significantly higher yield.

For a while it seemed as if glyphosate would avoid the fate of many other herbicides before it: the evolution of weeds resistant to herbicides. Glyphosate seemed to strike at such an essential part of their biology that no defense could possibly evolve. Of course, it also seemed for a while as if E. coli couldn’t evolve resistance to Michael Zasloff’s antimicrobial peptides. And after glyphosate-resistant crops had a few years to grow, farmers began to notice horseweed and morning glory and other weeds encroaching once more on their fields. Farmers in Georgia have had to destroy fields of cotton because of infestations of resistant Palmer amaranth. When scientists have studied these resurgent weeds, they’ve discovered genes that now make the plants resistant to glyphosate.

There’s no evidence that these weeds acquired their resistance from the transgenic crops. They most likely got it the old-fashioned way: they evolved it. Using glyphosate on transgenic crops proved to be so cheap and effective that farmers flooded huge swaths of land with a single herbicide. They created an enormous opportunity for weeds that could resist glyphosate and drove the quick evolution of stronger and stronger resistance. And once the weeds evolved their resistance, they appear to have passed on the resistance genes to other weedy species.

When