Walking upright on two legs is what makes us distinctly human. Chimpanzees can manage it for short stretches, but they lack the specialized anatomy that lets us stride easily across landscapes. Now, a new analysis of 7-million-year-old fossil bones suggests this ability emerged far earlier than scientists previously thought—reshaping our understanding of when and how our ancestors made this pivotal shift.
The fossils belong to Sahelanthropus tchadensis, a species that lived in Africa millions of years ago with a brain roughly the size of a chimp's. Yet Scott Williams, a paleoanthropologist at New York University, and his team found something unexpected in the bones: structural features consistent with bipedal walking. The femur—the thighbone—and the bony attachment point for a powerful leg ligament both show adaptations for upright movement. Their analysis, published in Science Advances, suggests Sahelanthropus was already walking on two feet.
Why does this matter? Bipedalism was transformative. It allowed early human ancestors to leave the forest canopy and venture into open grasslands and savannas. It freed the hands—no longer needed for knuckle-walking—for carrying, manipulating objects, and eventually making tools. This single shift opened new ecological niches and new possibilities for survival.
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Start Your News DetoxThe evidence isn't airtight. Williams and his colleagues worked with 3D models of limited fossil material: a crushed skull, some forearm bones, and a partial femur. Carol Ward, a paleoanthropologist at the University of Missouri, points out that the most telling bones—the knee joint and pelvis—haven't been found yet. Those would provide unambiguous proof of bipedalism. So the current findings are suggestive rather than definitive.
But that's how paleontology works. Each new fossil, each new analysis, adds a brushstroke to a picture drawn across millions of years. Scientists remain confident that further discoveries will clarify the timeline and mechanics of how bipedalism emerged. The story of how we learned to walk is far from finished—it's still being written in stone.
