An unprecedented agricultural experiment is being conducted at America's dinner tables. While none of the processed food we ate 20 years ago contained genetically engineered ingredients, now 75 percent of it does - even though the long-term human health and environmental impacts are unknown. The Food and Drug Administration doesn't require labeling of genetically engineered foods. In 1992, the FDA ruled that genetically engineered foods didn't need independent safety tests or labeling requirements before being introduced. But one of its own scientists disagreed, warning there were profound differences" with genetically engineered foods. Genetically engineered seed manufacturers were allowed to sell their products without telling consumers. A 2006 survey found that 74 percent of Americans had no idea that genetically engineered foods were already being sold. About 94 percent of U.S. grown soybeans are genetically engineered and contain a gene that protects them against glyphosate, now the nation's most widely used pesticide. Almost all the research on the safety of genetically engineered foods has been conducted by the companies that sell them. A recent poll found 93 percent of Americans think genetically engineered foods should be labeled. This month, 384,000 people signed a Just Label It (www.justlabelit.org) petition urging the FDA to mandate genetically engineered food labeling nationally.