“Our oldest representatives practiced bipedalism (on the ground and in trees),” said study author Franck Guy, a researcher at the University of Poitiers in France. The remains of ancient beings show that bipedalism arose shortly after the ancestors of chimpanzees and humans diverged in their evolutionary paths, he added.
There is still more to find in these fossils. Its characteristics show that Sahelanthropus tchadensis also retained the ability to climb trees proficiently, according to the study.
These ancestors were hominins, or species more closely related to humans than chimpanzees, and mark an early stage in our evolutionary divergence, said Daniel Lieberman, a professor of human evolutionary biology and a paleoanthropologist at Harvard University. Lieberman was not involved in the study.
Bipedalism in these ancestors isn’t exactly a surprise. The arm and leg bones analyzed in this study were found in Chad in 2001 along with a nearly complete skull, according to the study. However, it’s not clear if they came from the same individual, said study author Guillaume Daver, an assistant professor of paleontology at the University of Poitiers.
The skull showed a downward-pointing point where the head and spinal cord meet, a trait that would make walking on all fours much more difficult, Lieberman said.
New limb analysis from that find provides even more evidence that hominins traveled on two legs when they roamed the Earth about 7 million years ago, he added.
“It’s a glimpse into what put the human lineage on a separate evolutionary path from our ape cousins,” Lieberman said. While recent findings support what early studies already suggested, fossils from this era are rare, so each discovery is important evidence, she added.
And the new study “makes it quite unlikely that the common ancestor we share with chimpanzees looked like a chimpanzee,” Guy said.
Bipedalism set the fire
Bipedalism was extremely important to our evolution, but it didn’t make much sense to our ancestors, Lieberman said.
Walking on two legs makes the animal slower, more unstable and more at risk of back pain, none of which are useful for survival, he added.
“There must have been a big advantage,” Lieberman said. Scientists have a hypothesis about what it could have been.
Our common ancestor with apes looked a lot like a chimpanzee, and we know they need to use a lot of energy to walk — twice as much as humans when adjusted for body size, Lieberman said.
When the evolutionary paths of humans and chimpanzees diverged, Earth’s climate was changing and Africa’s rainforests were crumbling, so our ancestors had to travel farther to get food, he said. The hypothesis is that walking on two legs gave them more energy to travel.
“What really set us off on this different evolutionary path is that we were bipedal, or we walked on two legs,” Lieberman said. “It helps us really understand the origins of humanity.”
There are many things that define us as humans, such as language, tools and fire, he said. And in the 1870s, Charles Darwin, without any of the evidence we have now, surmised that walking on two legs was the spark that started it all, Lieberman said.
And now we can see that bipedalism was a big ape differentiator and free up our hands to develop tools, Lieberman said.
“We proved that Darwin was right,” he said. “That’s great”.
