Origins of Bipedalism

Why do we walk on two legs? If you asked a roomful of anthropologists, you'd likely not get the same answer from any two of them. Specialists cite everything from changing landscapes to needing to keep cool to heightening sexual attraction as probable causes of our upright stance, generally agreeing only on one point: that everyone else's hypothesis is wrong. Here, sample leading hypotheses and vote for the one that you prefer. Then hear paleoanthropologist Donald Johanson's take on all this.—Rima Chaddha

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