The gene is “one of the most powerful and dangerous ideas in the history of science,” argues Siddhartha Mukherjee in The Gene: An Intimate History. Since its discovery by Gregor Mendel, an obscure Moravian monk, the gene has been both a force for good and ill. In the 1930s, the Nazis exploited the pseudoscience of eugenics as a prelude to the Holocaust. Today, gene therapy holds out the hope of eradicating hereditary conditions like Huntington’s disease and even psychological disturbances, such as schizophrenia. [See how the DNA revolution is giving us unprecedented power.]

National Geographic caught up with the author as he was driving across the Williamsburg Bridge in New York City. Mukherjee, a professor of medicine at