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Since a few 6-million-year-old bones of the species Orrorin tugenesis were discovered in Kenya in 2000, scientists have not been certain that Orrorin could walk upright. A new analysis of the thighbone by biological anthropologists at The George Washington University and Stony Brook University asserts that it was indeed bipedal, and walked with a slow gait not unlike 4-million-year-old “Lucy,” the speciesAustralopithecus afarensis.

The common ancestor of chimpanzees and humans was thought to live between 5 and 7 million years ago. Orrorin may have been one of the earliest hominins to evolve the defining feature of upright walking.