October 7, 2022

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Ancient bones confirm that the earliest human ancestors walked upright

Ancient bones confirm that the earliest human ancestors walked upright

What may be the oldest known human ancestor, an ape man named Sahelanthropus tchadensis Who 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 walking on two legs – 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 SahelanthropusSaid Frank Gay, a paleoanthropologist at the University of Poitiers and a researcher at the French scientific agency CNRS, one of the study’s authors.

Jay and colleagues study, Published Wednesday in the journal Naturebased on a reassessment of three fossilized bones of the limbs – the femur of the thigh and two of the ulna of the forearm – found in the Chad desert on the southern edge of the Sahara more than 20 years ago.

a single skull of Sahelanthropus An individual, called Toma—meaning “life hope” in the local Daza language—was found at the same site, and there has been debate since then as to whether he was our ancestor. But the new study reinforces the suggestion that it was.

Researchers believe Sahelanthropus They lived just a few million years after the last common ancestor of modern humans – who also walk upright – and chimpanzees who don’t.

Although why our ancestors started walking on two legs is much debated by scientists, it is possible that walking on two legs led to larger brains to better control now the liberated forelimbs, which then evolved into human hands.

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3D shell thickness contrast map of the femur (left to right) of Sahelanthropus, an extant human, chimpanzee and gorilla (in back view). Frank Jay / Palivoprim / National Center for Scientific Research / University of Poitiers

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

Advanced intellectual abilities, such as the use of tools, language, and abstract thinking, are believed to have come much later.

“All we know at this point is that bipedal walking evolved long before brain enlargement and tool use,” said paleoanthropologist Johannes Haile-Selassie, director of the Institute of Human Origins at Arizona State University who was not involved in the latest study.

One distinguishing feature of Toma’s skull is that the spinal cord hole is placed in front of similar holes in monkeys that did not walk erect, indicating that their skull was on top of their spine, rather than in front of it.

Some previous evaluations of limb bones from the site suggested they could be from other individuals – Jay stresses. Sahelanthropus Maybe he didn’t walk upright after all.

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

file comparison Sahelanthropus Bones With the bones of other extinct apes and modern humans, as well as the bones of chimpanzees, gorillas and orangutans – our closest living relatives – researchers have determined that the ancient species may have been walking upright for most of the time.

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The arm bones, however, indicate Sahelanthropus It can also climb trees, both in a bipedal way – using its arms to stabilize itself, like modern humans – and in a quadrilateral way, in which its front limbs help it bear its weight.

Humanity separated from the chimpanzee group during the last Miocene, probably between 10 and 7 million years before the present.  This difference resulted in quite distinct shapes: the limb bones, for example, show differences associated specifically with the four-legged locomotion of chimpanzees and the bipedal locomotion of the remaining humans.
Humanity separated from the chimpanzee group during the last Miocene, probably between 10 and 7 million years before the present. This difference resulted in quite distinct shapes: the limb bones, for example, show differences associated specifically with the four-legged locomotion of chimpanzees and the bipedal locomotion of the remaining humans.
Frank Jay / Palivoprim / National Center for Scientific Research / University of Poitiers

study indicates Sahelanthropus It is indeed the oldest known human ancestor, although it is possible there were earlier ancestral species not yet found, said Guillaume Daver, associate professor of palaeoanthropology at the University of Poitiers and lead author of the study.

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

The results also indicate that Sahelanthropus The researchers wrote that they likely lived in an environment where walking on two feet on the ground and climbing trees was beneficial, such as mixed grasslands, forests, and palm groves – although the site in northern Chad where the fossils were found is a barren desert today.

One indication that Sahelanthropus One of the human ancestors was that the skull of Toma had relatively small canine teeth.

This is something seen in other human ancestors and modern humans but not in other modern apes, and scientists believe it may be a sign of reduced aggression.

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

This may be because walking upright evolved from the need to carry food to friends and relatives, which was itself a social adaptation to lower levels of aggression between individuals. “This may have been at the dawn of our origins,” Suwa said in an email.