Our oldest known ancestor could probably walk, say researchers
The oldest known ancestor of humankind walked on two legs but could still climb trees like an ape, a study of some 7m-year-old bones suggests.
Researchers analysed the fossil remains of Sahelanthropus tchadensis, unearthed 21 years ago in the deserts of Chad, central Africa. At the time, the discovery was said to have had “the impact of a small nuclear bomb” as it pushed back the ancestral line of hominids – the line leading to Homo sapiens – by a million years, closer to the split with chimpanzees.
The question as to whether the species walked upright remained unanswered. Now, a team in France say they are “pretty confident” that Sahelanthropus was indeed bipedal.
But other experts have expressed doubts about the study, published in the journal Nature, sparking debate about the lifestyle of Sahelanthropus and even whether it sits on our evolutionary branch.
The researchers examined a thigh bone and two forearm bones unearthed at the discovery site in the Toros-Menalla region of the Djurab desert in Chad. They analysed 23 features of the fossils that they say point to bipedalism and indicate a closer relationship to humankind 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 the obligate bipedalism in Homo,” said Jean-Renaud Boisserie, a co-author of the study from the University of Poitiers.
More recent hominid fossils, including the 3m-year-oldskeleton of Lucy, suggest bipedalism is a defining feature of our lineage.
“We are pretty confident,” said Franck Guy, also a 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.”
Prof Bernard Wood, of George Washington University, who was a coauthor of a previous study that concluded Sahelanthropus was not habitually bipedal, said: “These critically important fossils deserve better treatment than this shoddy paper provides. The study cherrypicks evidence, ignores recent studies that point to different conclusions than the ones the authors try to defend, and it fails to explore other equally, if not more likely, functional interpretations of these fossils.
“All of the three bones resemble chimpanzees more closely than any other living great ape, including modern humans. That does not mean Sahelanthropus was a chimpanzee, but it was likely closely related to chimpanzees, and its lifestyle was chimpanzee-like. It was not an upright,
ground-living ape of the kind that were likely to have been our earliest ancestors.”
Prof Fred Spoor, an expert in human origins at the Natural History Museum in London, who was not involved in the research, said the new study suggesting Sahelanthropus did walk on two legs appeared convincing.
“I think what is striking in this case is that as far back as 7m years ago, so close to the potential split with the line to chimpanzees, that even then there is a recognisable signal for bipedal behaviour. It really looks like being twolegged, 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 evidence presented, it could be arboreal or ground or both, and is mixed with climbing.”