Due to advances in molecular biology, it is now commonplace for scientists to transfer genes from one species to another, with the intention of designing novel organisms with attributes that can benefit humans. This new technology has been most successfully applied to plants. In fact, over the last two decades, scores of different crop species have been genetically engineered, meaning that the crops have been altered by the introduction of foreign genes. To date, the genetically engineered crops that have been approved for commercial production in the United States have been designed primarily to make farming easier and more cost-effective. For example, bacterial genes have been transferred into corn and cotton to produce insect-resistant varieties.