The findings indicate the ability to walk upright occurred in our ancestors more than 7 million years ago.
3D models of the postcranial material of Sahelanthropus tchadensis. From left to right: the femur, in posterior and medial view; the right and left ulnae, in anterior and lateral view.Franck Guy/ PALEVOPRIM/ CNRS / University of Poitiers
What may be the earliest-known human ancestor, an ape-man called Sahelanthropus tchadensis who lived in Africa roughly 7 million years ago, walked upright for much of the time, according to a new study.
The findings suggest that the ability to walk upright — known as bipedalism — occurred very early on the human family tree and reinforce the idea that it may be an evolutionary hallmark of our lineage.
“Our conclusion is that we have, most likely, features related to bipedal locomotion in Sahelanthropus,” said Franck Guy, a paleoanthropologist at the University of Poitiers and a researcher for the French scientific agency CNRS, who is one of the authors of the study.
The study by Guy and his colleagues, published Wednesday in the journal Nature, is based on a reassessment of three fossilized limb bones — a femur from a thigh and two ulnas from forearms — found in Chad’s Djurab Desert on the southern edge of the Sahara more than 20 years ago.
A single skull of a Sahelanthropus individual, dubbed Toumaï — meaning “hope of life” in the local Daza language — was found at the same site, and there’s been debate since over whether it was our ancestor. But the new study reinforces the suggestion that it was.
The researchers think Sahelanthropus lived only a few million years after the last common ancestor of modern humans — who also walk upright — and chimpanzees, who do not.
Although why our ancestors started walking on two legs is much debated by scientists, it’s likely that bipedalism led to bigger brains to better control now freed-up forelimbs, which then developed into human hands.
It’s also been suggested that walking upright is more energy efficient than climbing, and that early hominins faced a changing climate in which they had to be flexible about finding food.
Advanced intellectual abilities, like the use of tools, language and abstract thought, are thought to have come much later.
“All we know at this point is that bipedality evolved long before brain enlargement and tool use,” said paleoanthropologist Yohannes Haile-Selassie, the director of the Institute of Human Origins at Arizona State University who wasn’t involved in the latest study.
One of the distinctive features of the Toumaï skull is that the hole for its spinal cord is placed forward of similar holes in apes that didn’t walk upright, which suggests its skull was on top of its spine, rather than in front of it.