How did our species come to rule the planet? Rick Potts argues that environmental instability and disruption were decisive factors in the success of Homo sapiens: Alone among our primate tribe, we were able to cope with constant change and turn it to our advantage. Potts is director of the Smithsonian Institution's Human Origins Program, curator of anthropology at the National Museum of Natural History in Washington, D.C., and curator of the David H. Koch Hall of Human Origins, which opened at that museum last year. He also leads excavations in the East African Rift Valley and codirects projects in China that compare early human behavior and environments in eastern Africa with those in eastern Asia. Here Potts explains the reasoning behind his controversial idea.