Run, Lucy, Run! Human Ancestors Could Jog but Not Very Far or Fast

Run, Lucy, run! Human ancestors could run but not very far or fast

Who Gemma Conroy & Nature magazine

Early human relatives walked on two legs, like modern humans, but at a much slower pace, 3D computer simulations suggest. Australopithecus afarensis – a small hominin that lived more than three million years ago.

The analysis provides a detailed picture of hominin running speeds and the muscle adaptations that allowed modern humans to walk long distances, says Herman Pontzer, an evolutionary anthropologist at Duke University in Durham, North Carolina. “It’s a very deep view,” he says. The findings were published this week Current Biology.

A. afarensis it walked upright on two legs, making its fossil a favorite for researchers looking to unravel how bipedalism evolved in the human lineage. But few studies have looked at hominin running ability because it requires more than looking at fossilized remains and bones, says study author Karl Bates, a researcher in evolutionary biomechanics at the University of Liverpool, UK.

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Slow monkey

Bates and his colleagues created a digital 3D model of the skeleton of “Lucy,” a nearly 3.2-million-year-old child. A. afarensis A specimen found half a century ago in Ethiopia. They used the muscle characteristics of modern apes and the surface area of ​​Lucy’s bones to estimate the muscle mass of ancient hominins. The researchers then used a simulator to “run” the Lucy model and compared its performance to that of a digital model of a modern human.

The simulations showed that Lucy could run on two legs, despite lacking the long Achilles tendon and shortened muscle fibers that benefit modern humans’ endurance. But speed wasn’t Lucy’s strength: she could only top out at about five meters per second, even after researchers reengineered her with human muscles. In contrast, the human model walked at approximately 8 meters per second. Even though the researchers removed body size from their modeling, Lucy’s running lagged behind that of modern humans, suggesting that her physical proportions were the main culprit. “Even if you get all the muscles up, it was still slower,” says Bates.

Next, the researchers assessed whether certain muscles play a role in energy expenditure during running. When human-like ankle muscles were added to the Lucy model, the energy cost was comparable to that of other animals of similar size. But running became more difficult for Lucy when the team replaced human ankle muscles with monkey muscles. This suggests that adaptations of the Achilles tendon and surrounding muscles allow modern humans to run for long periods of time.

Bates and her colleagues plan to investigate whether fatigue and bone strain also affected Lucy’s running.

This article is and was reproduced with permission first published December 19, 2024.