Into the great debate over intelligence and instinct -- over what makes us human -- Susan Savage-Rumbaugh has thrown a monkey wrench. Her work with apes has forced a new way of looking at what traits are truly and distinctly human, and new questions about whether some abilities we attribute to "species" are in fact due to an animal's social environment. She believes culture and tradition, in many cases more than biology, can account for differences between humans and other primates.

Her bonobo apes, including a superstar named Kanzi, understand spoken English, interact, and have learned to execute tasks once believed limited to humans -- such as starting and controlling a fire. They aren't trained in classic human-animal fashion. Like human children, the apes learn by watching. "Parents really don't know how they teach their children language," she has said. "Why should I have to know how I teach Kanzi language? I just act normal around him, and he learns it."

Her latest book is Kanzi's Primal Language: The Cultural Initiation of Primates into Language.

Also, in 2011, she was named one of TIME's 100 Most Influential People.