University of Liverpool—The University of Liverpool has led an international team of scientists to take a fresh look at the running capabilities of Australopithecus afarensis, the early human ancestor famously represented by the fossil ‘Lucy’.
Karl Bates, Professor of Musculoskeletal Biology, convened experts from institutions across the UK and the Netherlands. Together they used cutting-edge computer simulations to uncover how this ancient species ran, using a digital model of ‘Lucy’s’ skeleton.
Previous work on the fossilized footprints of Australopithecus by multiple research teams has suggested that Lucy probably walked relatively upright and much more like a human than a chimpanzee. These new findings demonstrate that Lucy’s overall body shape limited running speed relative to modern humans and therefore support the hypothesis that the human body evolved to improve running performance, with top speed being a more critical driver than previously thought.
Professor Bates said: “When Lucy was discovered 50 years ago, it was by far the most complete skeleton of an early human ancestor. Lucy is a fascinating fossil because it captures what you might call an intermediate stage in Homo sapiens’ evolution. Lucy bridges the gap between our more tree-dwelling ancestors and modern humans, who walk and run efficiently on two legs.
“By simulating running performance in Australopithecus and modern humans with computer models, we’ve been able to address questions about the evolution of running in our ancestors.
“For decades scientists have debated whether more economical walking ability or improved running performance was the primary factor that drove the evolution of many distinctly human characteristics, such as longer legs and shorter arms, stronger leg bones and our arched feet. By illustrating how Australopithecus walked and ran, we have started to answer these questions.”
The team used computer-based movement simulations to model the biomechanics and energetics of running in Australopithecus afarensis, alongside a model of a human. In both the Australopithecus and human models, the team ran multiple simulations where various features thought to be important to modern human running, like larger leg muscles and a long Achilles Tendon, were added and removed, thereby digitally replaying evolutionary events to see how they impact running speed and energy use.
Muscles and other soft tissues are not preserved in fossils, so palaeontologists don’t know how large ‘Lucy’s’ leg muscles and other important parameters were. However, these new digital models varied the muscle properties from chimpanzee-like to human-like, producing a range of estimates for running speed and economy.
The simulations reveal that while Lucy was capable of running upright on both legs, her maximum speeds were significantly slower than those of modern humans. In fact, even the fastest speed the team predicted for Lucy (in a model with very human-like muscles) remained relatively modest at just 11mph (18kph). This is much slower than elite human sprinters, which reach peak speeds of more than 20mph (38kph). The models show the range of intermediate (‘jogging’) speeds that animals use to run longer distances (‘endurance running’) was also very restricted, perhaps suggesting that Australopithecus didn’t engage in the kind of long-distance hunting activities thought to be important to the earliest humans.
Professor Bates continued: “Our results highlight the importance of muscle anatomy and body proportions in the development of running ability. Skeletal strength doesn’t seem to have been a limiting factor, but evolutionary changes to muscles and tendons played a major role in enhancing running speed and economy.
“As the 50th anniversary of Lucy’s discovery is celebrated, this study* not only sheds new light on her capabilities but also underscores how far modern science has come in unravelling the story of human evolution.”
The study, ‘Running performance in Australopithecus afarensis’ was published in Current Biology (DOI:10.1016/j.cub.2024.11.025).
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Reconstruction of “Lucy”, Warsaw Museum of Evolution. Shalom, CC
BY-SA 3.0, Wikimedia Commons
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Article Source: University of Liverpool news release
*Running performance in Australopithecus afarensis, Current Biology, 6-Jan-2025. 10.1016/j.cub.2024.11.025
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