Stone Age farmers were, in a sense, the first genetic engineers. They started by planting the seeds of wild plants, and then later selected the most productive of their domesticated plants to provide the next year's seed stock. Over thousands of years, this process gave rise to the modern plant crops we now grow.

In the early 20th century, scientists practiced selective breeding by applying Gregor Mendel's classical laws of genetics to quicken the pace of crop improvements. Gregor Mendel discovered that when he took pollen from a male plant whose characteristics he liked and pollinated a female plant, their offspring took on the characteristics he had chosen. (Wells 12-13) This was important because, for the first time, scientists could breed the strongest, disease resistance, most nutritious and flavorful plant crops. But selective breeding, which involves sexual reproduction of plants and animals, has several limitations. First of all, these techniques are slow, and require years to make new crop varieties. Secondly, only closely related species can mate with each other; over time a primitive plant can become so different from its modern cousin that they can no longer interbreed. (Opposing Viewpoints 116)

Recent discoveries in biology have increased scientist's understanding of how genetic information is passed from cell-to-cell and generation-to-generation. Biologists recently learned about deoxyribonucleic acid, or DNA the molecule that codes the instructions of growth, maintenance, and reproduction of all living things. (Encarta 2000 1) Each instruction is called a gene. Once scientists had learned how to identify single genes of a desired trait, biologists developed a new technique that enabled them to not only transfer one gene from one plant to another, but also between plants and animals. They could now introduce new traits into a plant within a 9-month - 1 year span of time, instead of the 4 - 5 years it took with selective breeding. (Encarta 2000 1)

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