What is genetically modified food?

It comes from a plant or animal that has been genetically manipulated, usually by adding a gene from another organism, to give it desirable traits that can't be achieved through normal breeding. Since the first such genetically modified organism — the slow-rotting Flavr Savr tomato — was brought to market, in 1994, the GMO sector has boomed, and now an estimated 70 percent of processed food in the U.S. contains ingredients from crops altered in the lab to make them hardier, more resistant to disease and pests, and more tolerant of herbicides. You almost certainly consume GMO food all the time: 88 percent of the corn and 94 percent of the soy grown in the U.S. is genetically modified, and GMO crops are used to make the high-fructose corn syrup in soft drinks and the hydrolyzed vegetable protein in everything from soup mixes to salad dressings.

What does the California law propose?

Proposition 37, or "The Right to Know Genetically Engineered Food Act," would require that any food containing genetically modified ingredients be clearly labeled. If it passes on Nov. 6, some of America's most popular food products, from Coca-Cola to Corn Flakes, would have to be marked as "partially produced with genetic engineering" — a phrase that food companies fear could be as damning as a skull and crossbones. Similar labeling laws have been proposed in more than a dozen U.S. states, but the food and agriculture industries stopped them by putting intense political pressure on state legislators. This time the question will be decided by regular voters in a referendum. "To my mind, this is letting the free market work the way it's supposed to," said Rosa Rashall, a nutritionist who helped gather some of the 1 million signatures that put the proposition on the ballot. "Informed consumers decide what they want to buy."

What do food producers say?

They say a labeling law would be pointless and anti-scientific, and raise the price of food not only in California but in every state. Genetically altering a corn plant in the lab — splicing in, say, a bacterial gene that repels pests — is just a more sophisticated form of the selective breeding that early civilizations used to domesticate wheat 10,000 years ago. "It used to take several generations, getting the best from each plant, to get where you want to be," said Lisa Dry of Pioneer Hi-Bred, a DuPont subsidiary that creates and sells GMO seed. "Today, we isolate one gene that has a desired effect, one trait, and put it into the plant where you want." Only through such genetic modification, advocates say, will farmers achieve the higher yields necessary to feed a world population projected to reach 9 billion by 2050. They say labeling would hamper the spread of innovations like drought-resistant corn, no-lactose milk, and "golden" rice, a genetically fortified strain that developers say could end the vitamin A deficiency that kills 6,000 people a day in the developing world, including sub-Saharan Africa and India.

Are GMO foods harmful?

There's no scientific evidence that they are. The Food and Drug Administration maintains that GMO foods do not present "any different or greater safety concern than food developed by traditional plant breeding," and in June the American Medical Association said it saw "no scientific justification for special labeling of bioengineered foods." But opponents of GMO foods say the long-term effect of eating what they derisively call "Frankenfoods'' is unknown, arguing that the industry is turning unwitting people into guinea pigs in a massive experiment. It's possible, they contend, that the documented rise in allergies in recent years is the result of our bodies reacting badly to unnatural foods they do not recognize. "Californians have a right to know whether their baby formula, corn chips, or soy milk contain genetically modified ingredients that have not been proven safe," said Stacy Malkan, a pro–Proposition 37 campaigner. That "precautionary principle" is the basis of GMO labeling laws already in place in Australia, Brazil, China, Russia, and the European Union. In Europe, GMO ingredients now show up in only 5 percent of food.

Is the measure likely to pass?

Polls say 65 percent of California voters favor the law, but companies such as Monsanto, DuPont, Nestlé, and Coca-Cola are spending at least $25 million to change their minds in a "No to 37" campaign. If the labeling referendum passes, the food industry will undoubtedly fight the new law in court. Some advocates of GMO foods think it would be more effective to spend money persuading the public that "genetically modified" is a badge of progress rather than something to be feared. "One of the best ways the industry can turn public opinion around is to be honest, to be transparent," said Belinda Martineau, a plant scientist who helped develop the Flavr Savr tomato. That's a risk the biotech industry has so far been unwilling to take.

Superweeds through science

When Monsanto introduced its Roundup Ready seed in the late 1990s, grateful U.S. farmers quickly flocked to buy it. The soy and corn seeds had been genetically modified to tolerate the herbicide glyphosate, so killing weeds became cheaper and more effective, and crop yields soared. But nature is catching up. Weeds like waterhemp, mare's tail, and Palmer amaranth — also called "pigweed on steroids" — have developed resistance to glyphosate, growing into hulking, 6-foot-tall giants impervious to spraying. Such Roundup-resistant "superweeds" have taken root on at least 13 million acres of U.S. farmland, causing an estimated $1.9 billion in damage last year alone. Now Monsanto competitor Dow AgroSciences is seeking USDA approval for its Enlist line of genetically modified seeds, which are resistant to herbicides containing the potent agent 2,4-D. The geneticists' arms race with nature threatens to increase rather than reduce the use of toxic chemicals in agriculture, argues Margaret Mellon of the Union of Concerned Scientists. "This is not the path to sustainability."