Scientists may have just pushed back the timeline for when our ancestors first started walking upright.
A new study suggests that Sahelanthropus tchadensis, a species that lived about seven million years ago, was able to walk on two legs—making it one of the earliest known relatives of humans to show this crucial trait.
For years, researchers have argued over whether Sahelanthropus was truly bipedal. The species was discovered in the early 2000s in what is now Chad, in central Africa.
Most of the early attention focused on its skull, which showed a mix of ape-like and human-like features.
But without clear evidence from leg bones, scientists could not agree on whether it walked upright or moved mainly like a modern ape.
Now, a team of anthropologists has taken a fresh and detailed look at other bones found at the site, especially a thigh bone (femur) and a forearm bone (ulna).
Using advanced 3D imaging and careful comparisons with both living animals and fossil species, the researchers uncovered strong evidence that Sahelanthropus was adapted for walking on two legs.
The most important discovery is a small but crucial feature on the femur called a femoral tubercle.
This is the attachment point for the iliofemoral ligament, the strongest ligament in the human body.
This ligament helps keep the hip stable when standing and walking upright. Until now, this feature has only been found in hominins—species on the human family tree.
Its presence in Sahelanthropus strongly suggests that it regularly used a bipedal posture.
The researchers also confirmed two other traits linked to upright walking. One is a natural twist in the femur that helps the legs point forward, making walking more efficient.
The other is the structure of the muscles around the hips and buttocks, which help stabilize the body during standing and movement. These traits had been suggested before, but the new study provides stronger confirmation using modern analysis tools.
In addition, the team found that Sahelanthropus had relatively long legs compared with its arms. Apes typically have long arms and short legs, which suit climbing and swinging through trees.
Humans and early human ancestors, on the other hand, have longer legs, which are better for walking on the ground. While Sahelanthropus did not have legs as long as modern humans, its proportions were closer to early human ancestors than to apes.
Together, these features paint a clear picture. Sahelanthropus likely walked on two legs when on the ground, but it probably still spent a lot of time in trees. Its brain was about the size of a chimpanzee’s, and it likely climbed to forage for food and to stay safe from predators. In other words, it was not human—but it was also not just an ape.
This finding matters because it shows that bipedalism, one of the defining traits of being human, evolved very early.
It suggests that our lineage began walking upright long before large brains or advanced tools appeared. The ancestor that first took those steps may have looked much more like today’s chimpanzees and bonobos than like us.
By providing direct fossil evidence of upright walking, this study strengthens the case that Sahelanthropus tchadensis belongs on the human family tree—and that the story of how we became walkers on two legs began earlier than scientists once believed.
