Ancient bones confirm that the earliest known human ancestor walked upright

Ancient bones confirm that the earliest known human ancestor walked upright

Ancient bones confirm that the earliest known human ancestor walked upright

What may be the earliest known human ancestor, an ape-man called Sahelanthropus tchadensis that lived in Africa about 7 million years ago, walked upright for much of that 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 and reinforce the idea that it may be an evolutionary hallmark of our lineage.

“Our conclusion is that we most likely have 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 re-evaluation of three fossilized limb bones – a femur from a thigh and two ulnas from the forearms – found in Chad’s Djurab Desert on the southern edge of the Sahara. than 20 years ago.

A single skull of one Sahelanthropus individual, called Toumaï – meaning “hope of life” in the local Daza language – was found at the same site, and there has been debate since whether it was our ancestor. But the new study reinforces the suggestion that it was.

say the researchers 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 began walking on two legs is widely debated by scientists, it is likely that bipedalism led to larger brains to better control the now freed forelimbs, which then evolved into human hands.

Image: Sahelanthropus (Franck Guy/ PALEVOPRIM/ CNRS / University of Poitiers)

Image: Sahelanthropus (Franck Guy/ PALEVOPRIM/ CNRS / University of Poitiers)

It has also been suggested that walking upright is more energy efficient than climbing, and that early hominins faced a changing climate where they had to be flexible in finding food.

Advanced intellectual abilities, such as 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, director of the Institute of Human Origins at Arizona State University who was not involved in the latest study.

One of the distinguishing features of the Toumaï skull is that the hole for the spinal cord is located in front of similar holes in non-erect monkeys, suggesting that the skull was on top of the spine, rather than in front of it.

Some previous assessments of the limb bones from the site – Guy emphasizes that they could be from other individuals – suggested Sahelanthropus may not have gone upright after all.

But the latest study rejects that idea based on a battery of scientific tests that included biometric measurements and internal X-ray scans.

By comparing Sahelanthropus bones with those of other extinct apes and modern humans, as well as chimpanzees, gorillas and orangutans – our closest living relatives – the researchers determined that 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 their arms to stabilize themselves, like modern humans—and in a quadrupedal fashion, with their forelegs helping to carry their weight.

Humanity separated from the chimpanzee group during the recent Miocene, most likely between 10 and 7 million years before the present.  This divergence resulted in very distinct morphologies: the limb bones, for example, present differences specifically related to a quadrupedal locomotion for chimpanzees and a bipedal locomotion for extant humans.  (Franck Guy/ PALEVOPRIM/ CNRS / University of Poitiers)

Humanity separated from the chimpanzee group during the recent Miocene, most likely between 10 and 7 million years before the present. This divergence resulted in very distinct morphologies: the limb bones, for example, present differences specifically related to a quadrupedal locomotion for chimpanzees and a bipedal locomotion for extant humans. (Franck Guy/ PALEVOPRIM/ CNRS / University of Poitiers)

The study indicates Sahelanthropus is actually the earliest known human ancestor, although it is possible that there were even earlier ancestral species that have yet to be found, said Guillaume Daver, assistant professor of paleoanthropology at the University of Poitiers and the study’s lead author.

“In the future, we may find older hominins [human ancestors] remains that show forms of bipedalism … but we can also find older hominin remains that don’t show bipedalism,” he said.

The findings also indicate that Sahelanthropus probably lived in an environment where both ground bipeds and climbing trees were useful, such as mixed grasslands, forests and palm groves, the researchers wrote – although the site in northern Chad where the fossils were found is a barren desert today.

An indication of that Sahelanthropus was a human ancestor is that the Toumaï skull has relatively small canines.

It’s something seen in other human ancestors and modern humans, but not in other modern apes, and researchers think it could be a sign of reduced aggression.

The study suggests that both upright walking and smaller canines evolved around the same time, said Gen Suwa, a professor of paleoanthropology at the University of Tokyo who was also not involved in the study.

And it may be because walking upright evolved from the need to carry food to mates and relatives, which itself was a sociological adaptation to lower levels of aggression among individuals. “This may have been at the beginning of our origin,” Suwa said in an email.

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