Early human ancestors were far more efficient at walking upright than scientists had previously thought, a study has suggested. By comparing chimpanzees and humans walking, researchers noticed surprising similarities they say could have implications for the walking ability of hominin species Australopithecus afarensis.
Walking upright in humans is characterised by the co-ordinated movements of the hips and upper body – both move in opposite directions to allow for longer steps and to save energy. It was thought chimpanzees' torsos are too rigid to make this movement possible – but analysing their walking style has shown otherwise.
Researchers from the Stony Brook University in New York used kinematic analysis to look at the independent motions of the hips, lumbar and thorax in humans and two chimpanzees – Leo and Hercules – that had been trained to walk upright. The findings showed that Hercules and Leo's upper bodies do a small twist when they walk.
While the direction in which the thorax is aligned during strides differs with humans, the movement relative to the pelvis is almost identical between the two species. If you held the hips still, the ribs compensate for the movement by the same amount.
Publishing their findings in the journal Nature Communications, the authors say the chimpanzee-like morphology of early human ancestors like hominin Australopithecus afarensis would not have hindered them walking upright – and that this ability would have been present early on in hominin evolution.
"On the basis of similarities in trunk morphology with chimpanzees, Au. afarensis has been hypothesised as lacking an ability to rotate the thorax to counter pelvic rotations," they wrote. "However, the striking similarity in relative pelvis-to-thorax motion in humans and chimpanzees suggests that some ability of the thorax to counter pelvic rotations was also present in early hominins."
They said that while further research is needed to reach a consensus on the thoracic shape of early hominins, if some early species are found to have a more human-like ribcage this would support the idea that a more human-esque walking motion was possibly among our early ancestors.
"Our data show that regardless of the precise reconstruction of thoracic shape and lumbar length in the last common ancestor and other fossil hominins, counter rotations of the thorax and pelvis would have been feasible early in the evolution of human bipedalism."