Ancient Lucy Had Some Pretty Powerful Legs

Knee extensor muscles were like modern humans', meaning she could have walked like us: researcher
By Arden Dier,  Newser Staff
Posted Jun 15, 2023 9:55 AM CDT

Part of the reason the human ancestor known as Lucy is so famous is that her bones, discovered in Ethiopia in 1974, indicated her hominin species, Australopithecus afarensis, was among the first to walk on two legs more than 3 million years ago. But what would her long-vanished muscles tell us? "With recent advances in computational modeling, it is now possible to investigate these questions," says archaeologist Ashleigh Wiseman of Cambridge University, who set out to re-create Lucy's muscular anatomy in the hope of learning more about how she moved, per CNN. Was it fully upright like a modern human, or in the crouched posture of chimpanzees, whose bent hips and knees prevent a fully upright stance? The answer came through careful construction of digital muscle maps.

Inspired by the research of paleobiologist Oliver Demuth, who's created 3D musculoskeletal models of extinct archosaurs, Wiseman first used MRI and CT scans to create a muscle map of modern humans. She then analyzed virtual models of the Lucy fossil, gaining insight into how each joint could move, before laying muscles on top, taking direction from what Ars Technica describes as "a few telltale traces of scarring from where muscle had once connected to Lucy's fossilized bones." The end result indicated Lucy was powerfully built, with 36 muscles in each leg—the major ones were more than twice as large as those of modern humans, per a release. Almost 75% of Lucy's thighs were muscles (the rest being fat and bone), compared to around 50% in modern humans.

That was "very unsurprising," according to Wiseman, whose research was published Wednesday in Royal Society Open Science, per CNN. What was surprising was that Lucy's knee extensor muscles "were so comparable to the human" and would've allowed her to straighten her legs, Wiseman says. "If Lucy was a biped just like we are and walked exclusively on two legs, then she should be able to move in similar ways as we can." However, it's unlikely that Lucy walked exclusively. Australopiths are thought to have thrived both on the ground and in trees. "These reconstructions of Lucy's muscles suggest that she would have been able to exploit both habitats effectively," says Wiseman, per the release. Therefore, "Lucy likely walked and moved in a way that we do not see in any living species today." (More Lucy stories.)

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