Paleoanthropologists mark the divergence between apes and hominids with the adaptation ofbipedalism five to six million years ago. In this paper, I argue that while the first upright hominids occurred in this time frame, the process ofbecoming a fully efficient biped took much longer and was not complete until Homo erectus at 1.8 million years ago. To provide context to the puzzle ofhow and why our ancestors evolved upright walking, I examine many of the prevailing theories ofbipedal origins, including the aquatic ape hypothesis, the heat hypothesis, and the carrying hypothesis.



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