In 2001, high in the Sierra Norte de Oaxaca mountains of southern Mexico, UC Berkeley graduate student David Quist hiked along some of the world’s oldest cornfields. Quist was sampling cobs for DNA testing, and what he found kicked off a scientific firestorm and brought attention to a subtle threat to the future of global agriculture. In those ancient Mexican varieties, Quist detected the DNA signature of genetically modified (GMO) corn. A living …