New study shows that the earliest known human ancestors could walk upright

New analysis of ancient leg and hand bones found in Chad in 2001 led researchers to conclude that one of our earliest known ancestors was walking upright 7 million years ago.

A new study published Wednesday in the scientific journal Nature suggests that our ability to walk on two legs, or bipedalism, developed “shortly after the divergence of humans and chimpanzees.”

About 20 years ago, researchers in Chad discovered the nearly complete skull of Sahelanthropus tchadensis, the ancient ape species. They also found arm and leg bones nearby. The skull found had an opening in the middle of the skull that was oriented downward, suggesting that “like bipeds, Sahelanthropus balanced its head on a vertical neck,” human evolution expert Daniel Lieberman wrote in Nature.

3D models of the postcranial material of Sahelanthropus tchadensis. From left to right: the femur, in posterior and medial views. the right and left ulna, in anterior and lateral views. The remains were discovered in 2001 in Chad by the Franco-Chadian Paleoanthropological Expedition (MPFT). / Credit: Franck Guy/PALEVOPRIM/CNRS – University of Poitiers

However, not all scientists agree that the skull provided enough evidence for bipedalism, according to the Associated Press. Some believe that similar features between Sahelanthropus and humans could have evolved independently.

Scientists Guillaume Daver and Franck Guy, who co-authored the study, used the previously undescribed bones of the left thigh (femur) and forearm (ulna) to confirm the original findings. They found that the femur bone had “human-like” characteristics and looked “more like that of a bipedal hominid than a quadrupedal ape,” Lieberman explained.

On the other hand, the forearm bones looked “unmistakably chimpanzee-like,” with arms that could climb trees well.

Based on the evidence the researchers gathered from studying the skull and femur, they determined that the monkey likely walked upright, but could also climb well, Lieberman wrote.

Other than that conclusion, scientists don’t really have much information about the type of ride this species had, he said.

“We know little else about the gait of Sahelanthropus,” Lieberman said. “A mixed walking and climbing repertoire makes sense given that Sahelian lived near a forested lake.”

In addition, there are still many features that Sahelanthropus shares with chimpanzees, he wrote.

“This similarity makes sense if the last common ancestor of humans and chimpanzees was chimpanzee-like, and Sahelanthropus evolved very soon after humans and chimpanzees diverged,” Lieberman said.

The findings of this study are important because the development of bipedalism is considered “a decisive step in human evolution,” according to a press release from the Université de Poitiers in France, whose researchers were involved in the new study, as well as a previous study on the bones in 2005.

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