“Our earliest known representatives were bipedal (on the ground and in trees),” said study author Franck Guy, a researcher at the University de Poitiers in France. The remains of the ancient creatures show that bipedalism appeared soon after chimpanzees and human ancestors diverged in their evolutionary paths, he added. There is even more to be found in these fossils. Their characteristics show that Sahelanthropus tchadensis also retained the ability to climb trees well, 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, professor of human evolutionary biology and paleoanthropologist at Harvard University. Lieberman was not involved in the study. Bipedalism in these ancestors is not exactly surprising. The hand and foot bones analyzed in this study were found in Chad in 2001 along with a nearly complete skull, the study said. However, it is not clear whether they come from the same person, said study author Guillaume Daver, assistant professor of paleontology at the Université de Poitiers. The skull showed a downward-pointing point where the head and spinal cord meet — a feature that would make walking on all fours much more difficult, Lieberman said. The new analysis of the limbs from this find provides even more evidence that hominins were bipedal when they roamed the Earth about 7 million years ago, he added. “It’s a look at what set human ancestry on a separate evolutionary path from our ape cousins,” Lieberman said. While the recent findings support what early studies have already indicated, fossils from this era are rare, so any discovery is an important piece of evidence, he added. And the new study “makes it quite unlikely that the common ancestor we share with chimpanzees was chimpanzee-like,” Guy said.
Bipedism fueled 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 an animal slower, more unsteady and more at risk for back pain, none of which are helpful for survival, he added. “There must have been some really big advantage,” Lieberman said. Scientists have a hypothesis as to what this could be. Our common ancestor with apes was a lot like a chimpanzee, and we know they need a lot of energy to walk — twice as much as humans when you adjust for body size, Lieberman said. When the evolutionary paths of humans and chimpanzees diverged, Earth’s climate changed and rainforests in Africa fell apart, so our ancestors had to travel farther to find food, he said. The hypothesis is that walking on two legs gave them more energy to travel. “What really pushed us down this different evolutionary path is that we were bipedal, or walking on two legs,” Lieberman said. “It helps us really understand the origins of humanity.” There are many things that defined 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 — guessed that walking on two legs was the spark that started it all, Lieberman said. And now we can see that bipedalism was a big difference from apes and helped us free up our hands to develop tools, Lieberman said. “We proved Darwin right,” he said. “That’s kind of cool.”
