"We oppose the introduction of animal genes into plant foods," declares a pledge adopted at the 33rd World Vegetarian Congress. "When animal genes are inserted in bio-engineered foods, these plant foods are no longer truly vegetarian," argues an article in the Vegetarian Advocate.

It is easy to see how committed vegetarians, concerned as they are with animal welfare, might be worried about the effects of genetic engineering on the health and well-being of animals. But it is far from clear why vegetarians would object to inserting animal genes into plants. Ethical vegetarians want to prevent animal suffering. But genes have no feelings, no capacity to suffer, no desires of any kind. Genes are just sequences of the chemical bases adenine, cytosine, guanine, and thymine that provide recipes for combining amino acids to produce various proteins. Worrying about eating animal genes is akin to worrying about the ethical implications of eating a page out of a steak cookbook.

Consider the case of the "flounder tomato," often cited by vegetarian worrywarts. Flounder produce a kind of natural anti-freeze that allows them to thrive in arctic waters. In the early 1990s, the biotech company DNA Plant Technology inserted the gene responsible for this ability into tomato plants. The idea was to produce a tomato that could be frozen and thawed without becoming mushy. Unfortunately, the experiment didn't pan out. Consequently, despite the impression left by various activist Web sites, 11 years later no such tomatoes are being sold anywhere.

But what if the flounder tomato had been a success? Would eating one make the consumer a carnivore? Hardly. A report from the New Zealand government's Institute of Crop and Food Research calculates that the 1 million or so plant cells in a mouthful of a fruit or vegetable to which an animal gene had been added would contain less animal DNA than a single human cell.

Vegetarians (although not strict vegans, who eschew all animal products, including milk and eggs) already have a precedent to guide them on the issue of animal genes in food. Until 1990, the vast majority of cheese was produced using a curdling agent called rennet, the sole source of which was the linings of the fourth stomachs of slaughtered calves. Twelve years ago, the U.S. Food and Drug Administration approved a biotech version called chymosin, which is produced by yeast and bacteria into which the calf gene for the enzyme has been spliced. Now nearly 80 percent of all hard cheeses made in the United States are produced with the biotech enzyme. Many vegetarian groups have embraced cheeses made with chymosin as "vegetarian cheese." They recognize that an animal gene spliced into a fungus is saving millions of calves from being slaughtered for their rennet. Surely this is an animal-friendly result.

Incidentally, another advantage is that biotech chymosin makes cheeses kosher and halal. Observant Jews and Muslims no longer have to worry whether the enzyme used for curdling comes from calves slaughtered according to religious requirements.

If some vegetarians are concerned about animal genes in plants, perhaps we should all be worried about cannibalism. After all, researchers have spliced human genes into plants and animals. Again, so what? These human genes are not to be confused with actual human beings; they are recipes for useful proteins that might be used as medicines, not fingers or toes that might serve as macabre hors d'oeuvres.

Besides, people eat human genes all the time. Breast-fed babies, for example, typically consume more than 200,000 human cells from their mothers per milliliter of milk. And as the New Zealand report notes, "the simple act of a passionate kiss or oral sex may result in the consumption of considerably more animal DNA, from another individual, than [would] eating a mouthful of a transgenic plant containing an animal gene."

In any case, as Canada's National Institute of Nutrition points out, "There really is no such thing as an 'animal gene' or a 'plant gene.' In fact, humans have many genes in common with other animals, plants and even bacteria." Mexican plant geneticist Luis Herrera-Estrella likewise notes that "about 60% of the plant genes have very similar copies in animals." This is not surprising, since all living things share the same genetic toolbox.

Not all vegetarians are confused on this issue. Microbiologist Emanuel Goldman of the New Jersey Medical School, for example, tried to persuade the World Vegetarian Congress that animal genes inserted into bacteria, yeast, or plants offer "the most realistic opportunity yet" to free humanity from having to kill or exploit animals. Thoughtful vegetarians should resist being co-opted by the anti-biotech movement.