When We First Stood Up: New Fossils Pinpoint the Moment Our Ancestors Walked on Two Feet

Ancient Bones Rewrite the Timeline of Human Upright Walking

In the arid badlands of northern Kenya, a team of paleoanthropologists has uncovered a set of 7-million-year-old thigh and shin bones that they say capture the instant our primate relatives stopped knuckle-walking and began striding like modern humans.

The Discovery That Changes Everything

Led by Dr. Amina Hassan of the University of Nairobi, the researchers used micro-CT scans to peer inside the mineralized shafts. What they found were tell-tale patterns of cortical bone thickness—an internal signature of habitual upright walking.

"For the first time we can say, with forensic certainty, that this creature spent more time on two legs than four," Hassan told reporters at the site.

Why This Matters for Human Evolution

Until now, the earliest widely accepted evidence of bipedalism dated to 6 million years ago—nearly a million years younger. The new find pushes back the timeline and suggests that walking upright may have evolved in open woodlands rather than the grassy savannas long invoked in textbooks.

• The bones show a valgus knee angle, aligning the foot under the body’s center of gravity.
• Isotope analysis of surrounding soil indicates a mixed environment of trees and seasonal grass.
• No upper-limb fossils were recovered, but the leg anatomy alone is enough to classify the specimen as an early biped.

From Forest Canopy to Open Ground

By standing up, our ancestors gained a vantage point to spot predators and freed their hands for carrying food and tools. Over evolutionary time, these small advantages compounded, setting the stage for larger brains and, eventually, language.

What Happens Next

The Kenyan team will return to the field next dry season, hoping to uncover pelvic or spinal fossils that could confirm whether this species also possessed the S-shaped spine characteristic of modern humans.