They cite studies indicating that plants engineered to make their own insecticides can accelerate the evolution of resistant insects and may ultimately render the few remaining organic insecticides ineffective. And they note that crops engineered to be tolerant of chemical weedkillers can lead to more widespread use of those chemicals, which could wipe out weedy homes for beneficial insects and harm the birds that feed on those insects. Separately, some critics have raised the possibility that genetically modified foods may harm people's health. No adverse effects have been documented, they concede. Studies suggest that bacteria in people's or animals' intestines may be able to pick up those genes from digested food and perhaps accelerate the evolution of antibiotic-resistant microbes.
Allergies are a potential problem, too, critics note.
Two years ago, scientists tried to make soybeans more nutritious by inserting into them a Brazil nut gene. Nonetheless, some people fear that consumers with rare allergies may suffer life-threatening reactions to other foods harboring unlabeled foreign genes. Only now is research starting to examine all these potential risks to see how likely they are in reality. Unfortunately, the picture remains unclear. A new report sponsored by BIO, for example, concluded last month that agricultural biotechnology has increased crop yields, reduced farmers' use of pesticides and herbicides and reduced soil erosion in the United States.