Seven Million Year Old Ape Confirms Earliest Evidence of Human Bipedalism

Revolutionary Discovery in Human Evolution

A groundbreaking analysis of ancient fossil bones has provided the strongest evidence yet that our earliest known ancestor walked upright seven million years ago. Scientists have found strong anatomical evidence that Sahelanthropus tchadensis was bipedal, including a ligament attachment seen only in human ancestors, making it capable of upright walking .

Sahelanthropus tchadensis was essentially a bipedal ape that possessed a chimpanzee-sized brain and likely spent a significant portion of its time in trees, foraging and seeking safety. Despite its superficial appearance, Sahelanthropus was adapted to using bipedal posture and movement on the ground .

The species, discovered in Chad's Djurab desert by Michel Brunet, a French paleontologist, between July 2001 and March 2002 , has sparked intense debate for over two decades about whether it truly represents humanity's earliest ancestor or simply another extinct ape.

The Smoking Gun Evidence

Using advanced 3D imaging along with other analytical techniques, the research team identified a femoral tubercle in Sahelanthropus. This small but important structure serves as the attachment point for the iliofemoral ligament, the strongest ligament in the human body and a critical component for standing and walking upright .

The discovery is particularly significant because the femoral tubercle provides attachment for the iliofemoral ligament linking the pelvis to the femur and has so far been identified only in hominins . This anatomical feature represents what researchers call a "smoking gun" for bipedalism—a trait found exclusively in species that walk upright.

Scott Williams, the NYU anthropologist who led the research, explains that the analysis revealed three key features that point to bipedalism in Sahelanthropus: the presence of a femoral tubercle, a natural twist within the range of hominins in the femur that helps legs to point forward, and gluteal muscles similar to those in early hominins that keep hips stable and aid in standing, walking, and running .

Rewriting the Human Story

The implications extend far beyond a single species. The researchers also found that Sahelanthropus had a relatively long femur compared to its ulna, which adds further support for bipedal behavior. Apes typically have long arms and short legs, while hominins show the opposite pattern. Although Sahelanthropus had shorter legs than modern humans, its limb proportions differed from those of apes and more closely resembled Australopithecus .

This finding places bipedalism near the very root of the human family tree, suggesting that if Sahelanthropus truly combined chimpanzee-like climbing with meaningful adaptations for upright walking, then bipedalism may have started as a flexible strategy, not a sudden switch .

Williams concludes that their analysis offers direct evidence that Sahelanthropus tchadensis could walk on two legs, demonstrating that bipedalism evolved early in our lineage and from an ancestor that looked most similar to today's chimpanzees and bonobos .

The Ongoing Scientific Debate

Despite this compelling new evidence, the scientific community remains divided. A 2024 study by Cazenave et al. re-examined postcranial evidence, and concluded that it is not sufficient to determine whether Sahelanthropus was a habitual biped, since none of the features are consistent with or unique to bipedal hominins . Other researchers have questioned whether the fossil bones even belong to the same species.

The debate reflects the challenges of interpreting fragmentary fossils from such ancient time periods. As Harvard paleoanthropologist Dan Lieberman notes, "It's not a slam dunk," because the partial fossil thighbone lacks both ends , which typically contain the most diagnostic features for determining locomotion.

However, the new study's comprehensive approach—combining multiple analytical methods and identifying features unique to bipedal species—represents the most thorough examination to date of these crucial fossils. The research suggests that the transition to upright walking began much earlier than previously thought, fundamentally reshaping our understanding of what it means to be human.