What is perhaps the earliest known human ancestor called an ape-man? Sahelanthropus tchadensis which lived in Africa about 7 million years ago, walked upright most of the time, according to a new study.
The findings suggest that the ability to walk upright — known as bipedalism — occurred very early in the human family tree, reinforcing the idea that it may be an evolutionary feature of our lineage.
“Our conclusion is that, most likely, we have features associated with bipedal locomotion sahelanthropussaid Franck Guy, a paleoanthropologist at the University of Poitiers and a researcher for the French scientific agency CNRS, one of the authors of the study.
Guy and colleagues’ study, published Wednesday in the journal Nature, is based on a reassessment of three fossilized limbs — a femur of a thigh and two ulnas of forearms — found in Chad’s Djurab Desert on the southern edge of the United States. Sahara. than 20 years ago.
A single skull of a sahelanthropus individual, named Toumaï – meaning ‘hope of life’ in the local Daza language – was found in the same spot and there has been debate ever since as to whether it was our ancestor. But the new study bolsters the suggestion that it was.
The researchers think sahelanthropus lived just a few million years after the last common ancestor of modern humans — who can also walk upright — and chimpanzees, who don’t.
While scientists have much debate about why our ancestors started walking on two legs, it’s likely that bipedalism led to larger brains to better control the now-released forelimbs, which then evolved into human hands.
It has also been suggested that upright walking is more energy efficient than climbing, and that early hominids faced a changing climate in which they had to be flexible in finding food.
Advanced intellectual abilities, such as the use of tools, language and abstract thinking, are said to have emerged much later.
“All we know at this point is that bipedalism evolved long before the brain was enlarged and tools were used,” said paleoanthropologist Yohannes Haile-Selassie, the director of the Institute of Human Origins at Arizona State University, who is not involved. was in the last study.
One of the distinguishing features of the Toumaï skull is that the hole for the spinal cord is placed in front of similar holes in monkeys that did not walk upright, suggesting that the skull lay on top of its spine rather than in front of it.
Some previous reviews of the site’s limbs – Guy emphasizes they could be from other individuals – suggested sahelanthropus maybe not walking upright.
But the latest study rejects that idea based on a series of scientific tests that include biometric measurements and internal X-ray scans.
By comparing the sahelanthropus bones with those of other extinct apes and modern humans, as well as those of chimpanzees, gorillas and orangutans — our closest living relatives — the researchers determined the ancient species probably walked upright most of the time.
However, the arm bones indicate: sahelanthropus could also climb trees, both in a bipedal fashion – using its arms to stabilize itself, like modern humans – and in a quadrupedal fashion, with its front legs helping to support its weight.
The study indicates: sahelanthropus is indeed the earliest known human ancestor, although it’s possible there were even earlier ancestor species that have not yet been found, said Guillaume Daver, an assistant professor of paleoanthropology at the University of Poitiers and the lead author of the study.
“In the future we may find older hominids” [human ancestors] remains that show forms of bipedalism … but we can also find older hominid remains that do not show bipedalism,” he said.
The findings also suggest that sahelanthropus likely lived in environments where both ground bipeds and climbing trees were useful, such as mixed grasslands, woodlands and palm groves, the researchers wrote — although the site in northern Chad where the fossils were found is today a barren desert.
An indication that sahelanthropus was a human ancestor is that Toumaï’s skull has relatively small canine teeth.
You see that in other human ancestors and modern humans, but not in other modern apes, and scientists think it could be a sign of decreased aggression.
The study suggests that both upright walking and smaller canines evolved at about the same time, said Gen Suwa, a professor of paleoanthropology at the University of Tokyo who was also not involved in the study.
And that may be because upright walking evolved from the need to carry food to friends and relatives, which itself was a sociological adaptation to lower levels of aggression among individuals. “This may have been at the beginning of our origins,” Suwa said in an email.