Origins of Bipedalism

Apie

Why do we walk on two feet? If you asked a roomful of anthropologists, you'd likely get a different answer from each person. In the course of human evolution, was there one key factor—changing landscapes, the need to keep cool, the advantage of attracting a mate? Here, sample leading hypotheses and vote for the one you prefer. Then hear paleoanthropologist Donald Johanson's take.