A groundbreaking new study has reignited a fierce scientific debate over the identity of humanity's earliest known ancestor, focusing on a mysterious ape-like creature that roamed Africa seven million years ago.
The Fossil at the Heart of the Debate
At the centre of the controversy is Sahelanthropus tchadensis, a species known only from a handful of fossils unearthed in the Djurab desert of Chad in 2001. The lead researcher of the original discovery, Professor Michel Brunet from the University of Poitiers, France, boldly declared it "the ancestor of all humankind," suggesting it walked upright based on the positioning of its skull.
However, the claim was met with scepticism. Without crucial bones from the lower body, scientists struggled to definitively prove how Sahelanthropus moved. The later discovery of a partial thigh bone and forearm bones did little to settle the argument, leaving a key chapter in our evolutionary story frustratingly blank.
A Fresh Look at Ancient Bones
Now, a team led by Dr Scott Williams of New York University has conducted a fresh, high-tech analysis of these contentious limb bones. By comparing their size, proportions, and 3D contours with those of known hominins and apes, they sought conclusive evidence.
The researchers identified several features they argue are hallmarks of upright walking. A key piece of evidence is a structure on the thigh bone called the femoral tubercle. "It’s the attachment point for the largest and most powerful ligament in our bodies," explained Dr Williams. "It’s a really important adaptation for bipedal walking and, as far as I know, this has only been identified in bipedal hominins."
The team also noted a natural twist in the thigh bone that helps the leg point forward, and evidence of buttock muscles that stabilise the hips during standing and walking. Their findings, published in Science Advances, paint a picture of an "ape-like animal" that lived around the time of the evolutionary split from chimpanzees and was adapted to walking on two legs on the ground, while still likely using trees for foraging and safety.
Unconvinced Critics and the Path Forward
Despite the new analysis, the case is far from closed. Critics point out that many of the bone features still resemble those of African great apes. Dr Marine Cazenave of the Max Planck Institute for Evolutionary Anthropology called the evidence for bipedalism "weak," noting the femoral tubercle is in a damaged area of the bone and may not be directly linked to upright walking.
Dr Rhianna Drummond-Clarke, from the same institute, suggested the evidence could equally point to Sahelanthropus being an early chimpanzee ancestor that later evolved into a knuckle-walker.
The one point of universal agreement among researchers is the need for more fossils. Dr Guillaume Daver and Dr Franck Guy from the University of Poitiers, who support the bipedalism theory, hope new discoveries will be made when the Chadian-French team returns to the site later this year. As Dr Williams succinctly put it, the core problem remains: "I think it’s a case of too few fossils and too many researchers." The quest to find our earliest upright ancestor continues.
