In the mid-twentieth century, American plant breeders, frustrated by their dependence on natural variation in creating new crops and flowers, eagerly sought technologies that could extend human control over nature. Their search led them to celebrate a series of strange tools: an x-ray beam directed at dormant seeds, a drop of chromosome-altering colchicine on a flower bud, and a piece of radioactive cobalt in a field of growing crops. According to scientific and popular reports of the time, these mutation-inducing methods would generate variation on demand, in turn allowing breeders to...