If you eat, and you're American, that means you're putting genetically modified substances into your body. "Transgenic" plants, which existed only in laboratories a decade ago, have become sufficiently common that already roughly one-half of the U.S. soybean crop and one-third of the corn crop are sprouting from genetically engineered seeds. Some tomatoes, papayas, potatoes, squash, and other crops now occur in genetically modified varieties, and more such plants are on the way. Owing to the ubiquitous use of corn sweeteners and soy-based oil in processed foods, it's now close to impossible to avoid consuming genetically engineered crop by-products. Even wandering down the organic-foods aisle may not help. Mori-Nu brand tofu, popular in California, now carries a cryptic label announcing that it contains "a full spectrum of naturally occurring isoflavones, including genistein." For those of you who aren't Ph.D. nutritionists, this means the tofu is made from gene-engineered soy.

Should we worry about genetically modified farming? Opposition to genetically modified crops was a theme of the December 1999 riots at the World Trade Organization meeting in Seattle. Many activists, including many people of faith, are leery of this new technology. Opposition in Europe is particularly intense. Fear of scientific tampering with the food supply is not irrational: we all have a clear self-interest in knowing whether food is healthful and wholesome. Even if it turns out that genetically engineered crops are safe, will they alter our relationship with our daily bread?

Today, few Americans worry about whether they will have food on the table, though we must never forget the estimated 800 million people worldwide who are malnourished. (For United Nations updates and donation information on global food needs, see www.thehungersite.com.) But beyond keeping us alive, our daily bread provides one of the day's reliable pleasures, to say nothing of a connection to the cycle of life. Break a piece of freshly baked bread, preferably with a friend: the warm, expanding aroma is the scent of biology itself, what the Bible calls a "sweet savour." Gene-engineered bread--will it have the same savour?

So far, there's no indication that genetically modified crops have caused any harm to human health. The genes being moved around in "transgene" plant breeding aren't lab products; rather, they're naturally occurring DNA that have caused no harm in the organisms from which they were taken. For this reason, the National Academy of Sciences and the American Medical Association have said there are no known health risks with genetically engineered crops.

Some aspects of transgenic food, in fact, are good for you. Thoseisoflavones, for example, are a healthful protein, which some studies associate with reduced cancer risk. Soybeans are being genetically engineered to include isoflavones to make them more nutritious; other soy engineering projects seek to reduce the bean's content of polysaturated fat, allowing for lower-fat vegetable oil. Plant biologists are attempting to use genetic engineering to splice the allergens out of peanuts, add vitamins to potatoes, and achieve other improvements. Some researchers, for example, are splicing cauliflower DNA into potatoes, so that potatoes can contain beta carotene, a precursor to vitamin A that's linked to lower heart disease, according to some studies. If a cauliflower gene is inserted into a potato, does this create something fundamentally unnatural, or represent merely a high-tech extension of the selective breeding that has produced what we now think of as "traditional" crops? Bear in mind that modern high-yield wheat barely resembles the Middle Eastern grasses from which it was originally bred; today's full, rich high-yield maize is unrecognizable next to its ancestor teosinte, the wispy Mexican plant that North Americans began selectively breeding several thousand years ago.

Almost nothing grown on today's farms, including on organic farms, is wholly natural. And it seems that hasn't hurt us: Americans live longer every year, with better health indices on almost every point, including declining rates of most cancers.

Then there are the environmental questions raised by genetically engineered crops. Most of the transgene corn now grown in the United States has been DNA-spliced to make its own bacillus thuringiensis (B.T.), a naturally occurring microorganism that kills farm pests such as the European corn borer. Corn with B.T. is essentially its own pesticide, and the use of pesticides by American farmers appears to be dropping as transgene crops are adopted. (BT has no known effect on human health; organic farmers have been spraying it on crops for decades.) But B.T. corn might have unwelcome environmental effects; some preliminary tests suggest that its pollen may kill the caterpillar of the monarch butterfly. Once millions of acres of B.T. corn are planted, it seems inevitable that insects that are resistant to this natural pesticide will evolve; the B.T. gene may also "outcross" into wild plants, causing weeds with built-in insect resistance.