Mankind’s oldest known ancestor walked on two legs but could still climb trees like a monkey, according to a study of bones 7 million years old.
Researchers have analyzed the fossil remains of Sahelanthropus tchadensis, unearthed 21 years ago in the deserts of Chad, Central Africa. At the time, the discovery would have had “the impact of a small nuclear bomb” because it pushed back the ancestral line of hominids – the line leading to Homo sapiens – a million years, closer to the split with chimpanzees.
Whether the species walked upright remained unanswered. Now a team in France say they are “fairly confident” that sahelanthrope was bipedal.
But other experts have cast doubt on the study, published in the journal Nature, sparking debate about the lifestyle of the sahelanthrope and even if it relies on our evolutionary branch.
Researchers examined a thigh bone and two forearm bones discovered at the find site in the Toros-Menalla region of Chad’s Djurab desert. They analyzed 23 features of the fossils that they believe point to bipedalism and point to a closer relationship with humanity than apes.
“We can conclude from the evidence that we have habitual bipedalism, plus quadrupedal arborealism, which is what is observed for early hominids, and then gradually turns into obligate bipedalism in Homosaid Jean-Renaud Boisserie, co-author of the study from the University of Poitiers.
More recent hominid fossils, including one 3 m years old skeleton of Lucy, suggest that bipedalism is a defining characteristic of our lineage.
“We are quite confident,” said Franck Guy, also co-author. “What we show is that the morphological pattern of the femur is more similar to what we know in humans, including fossil humans, than in apes.”
Professor Bernard Wood, of George Washington University, co-author of a previous study concluding sahelanthrope was not usually bipedal, said: “These crucially important fossils deserve better treatment than that provided by this shoddy article. The study selects evidence, ignores recent studies that point to different conclusions than the authors are trying to defend, and it fails to explore other equally, if not more likely, functional interpretations of these fossils.
“The three bones look more like chimpanzees than any other living great ape, including modern humans. That’s not to say sahelanthrope was a chimpanzee, but he was probably closely related to chimpanzees and his way of life resembled that of chimpanzees. It was not an upright, ground-dwelling ape of the kind that would probably have been our earliest ancestors.
Professor Fred Spoor, a human origins expert at the Natural History Museum in London, who was not involved in the research, said the new study suggested sahelanthrope walked on two legs looked convincing.
“I think what’s striking about this is that 7 million years ago, so close to the potential split with the chimpanzee lineage, that even then there is a recognizable signal of bipedal behavior It really seems like being bipedal, being bipedal, is the defining nature of our evolutionary tree,” he said.
Dr Sandra Martelli, an associate professor at University College London, who was also not involved in the study, said: ‘The type of bipedal locomotion cannot be decided on the basis of the evidence presented, it can be arboreal or terrestrial or both, and is mixed with climbing.”
Our oldest known ancestor could probably walk, researchers say