This Strolling Ape May Be the Earliest Human Ancestor

Whenever you’re taking a stroll, you reap the benefits of a key function that separates us from our ape family—bipedalism, or strolling upright on two legs. 

Fossils with indicators of this trait can level scientists to our earliest human ancestor, or the primary member of the hominin group that features fashionable and extinct people. A potential candidate for this historical relative: Two many years in the past, scientists introduced the identification of Sahelanthropus tchadensis, a hominin species from round 7 million years in the past—across the time when people cut up from apes.

Back then, researchers had examined jaw bits, tooth, and most of a skull from S. tchadensis, which have been present in what’s now the nation of Chad. More latest analysis has zeroed in on two items of forearm bones and a part of a thigh bone or femur that have been later recognized as belonging to the identical species.

Since S. tchadensis was unveiled, scientists have squabbled over the likelihood that it was bipedal. Some have even questioned whether or not the creature was a hominin in any respect.

Now, evaluation of limb bones from this species recommend that it might certainly stroll on two legs. While the bones they noticed look much like these of chimpanzees, they discovered a number of compelling items of proof of bipedalism, findings reported in Science Advances.

A workforce from throughout the United States took an in depth have a look at these bones and found a key indicator of bipedalism: a femoral tubercle, a bony bump on the femur the place the iliofemoral ligament attaches; it’s the largest and strongest ligament within the human physique, and hyperlinks the femur to the pelvis. This function has solely been present in bipedal hominins, and it’s a essential ingredient for upright strolling. 

Read extra: “How Posture Makes Us Human”

They additionally confirmed hominin-like particulars within the bones that have been pinpointed in previous research: a twist within the femur that helps orient the legs ahead, and muscle tissue that maintain the hips steady and help in strolling, standing, and working. Additionally, the femur was comparatively lengthy in contrast with the ulna, a bone within the forearm, one other trace of bipedalism.

S. tchadensis did have shorter legs than fashionable people, however its femur size wasn’t too far off from a pattern taken from Australopithecus, a genus of early hominins that advanced round 4 million years in the past.

Overall, the proof means that “bipedalism evolved early in our lineage and from an ancestor that looked most similar to today’s chimpanzees and bonobos,” stated examine co-author Scott Williams, an evolutionary morphologist at New York University, in a statement.

This species “was essentially a bipedal ape that possessed a chimpanzee-sized brain,” Williams added. It appears to have spent a lot of its days in bushes, looking for out meals and security, however was tailored to stroll on the bottom. S. tchadensis could provide an instance of an “early form of habitual, but not obligate, bipedalism,” the authors famous within the paper, as they suppose bipedal habits grew over the course of evolution earlier than it turned a extra closely utilized hominin attribute.

Ultimately, the trail towards traversing the world on two legs could have confirmed a marathon, not a dash.

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Lead picture: Didier Descouens / Wikimedia Commons

• Molly Glick

  Posted on January 2, 2026

  Molly Glick is the e-newsletter editor of Nautilus.