Lydia M. Hopper is a primatologist who studies how monkeys and apes innovate and learn new skills. She is the assistant director of the Lester E. Fisher Center for the Study and Conservation of Apes at Lincoln Park Zoo in Chicago, IL, where Stephen R. Ross is the director. Ross's research focuses primarily on chimpanzee behavior, cognition, and welfare. He is coeditor of The Mind of the Chimpanzee: Ecological and Experimental Perspectives, also published by the University of Chicago Press.