A research team led by Stony Brook University investigating human and chimpanzee locomotion have uncovered unexpected similarities in the way the two species use their upper body during two-legged walking. The results, reported in Nature Communications , indicate that our early human ancestors, including the famous fossil ‘Lucy’ (a species known as Australopithecus afarensis), may have been able to use their torsos to increase walking efficiency in the same way as modern humans. The research team used high-speed cameras to track and compare how the torsos of humans and chimpanzees actually moved during bipedal walking. They studied the movements by way of three-dimensional kinematic analyses and computer-generated comparisons. They discovered that the main difference between human and chimpanzee bipedalism is that chimps swing their hips much more. “Only when our early ancestors were able to reduce this hip rotation were their upper bodies able to play a human-like role in promoting efficient bipedal walking,” said Thompson. “When this actual transition occurred is still an open question.”