THERE HAS BEEN a revolution in the world of genetics. It is called epigenetics. The Greek prefix “epi” implies something that comes in addition to something else; epigenetics adds to the study of genes the study of how they get turned on or off. Although a Martian eavesdropping on conversations about genetics in the popular media would surely conclude that genes and traits correspond in a one-to-one ratio, in reality the twenty thousand to twenty-five thousand genes in the human genome do not automatically spawn traits. Read more...