One cannot overemphasize the role of bipedalism in hominid development. It stands as perhaps the salient point that differentiates the forebears of man from other primates. This unique ability freed the hands for myriad possibilities -- carrying, tool-making, intricate manipulations. From this single development, in fact, stems all modern technology.
(From Mary Leakey, "Footprints in the Ashes of Time." National Geographic, April 1979)
Summarize the different hypotheses offered to explain the development of bipedalism and the evidence that supports or refutes each.