Lucy, an early human ancestor, could run upright but much slower than modern humans. New simulations show that muscle and tendon evolution, not just skeletal changes, were key to improving human running speed.
The University of Liverpool has led an international team of scientists in a new investigation into the running abilities of Australopithecus afarensis, the early human ancestor best known through the famous fossil “Lucy.”
Professor Karl Bates, an expert in Musculoskeletal Biology, brought together specialists from institutions in the UK and the Netherlands. Using advanced computer simulations and a digital reconstruction of Lucy’s skeleton, the team explored how this ancient species might have moved and run.
Walking Upright but Running Slowly
Previous studies of Australopithecus fossilized footprints by various research teams have suggested that Lucy likely walked upright and in a manner more similar to humans than chimpanzees. However, these new findings reveal that Lucy’s body shape restricted her running speed compared 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 of 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.”
Simulating Evolution Through Digital Models
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 paleontologists 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.
Limited Running Speed and Endurance
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 unraveling the story of human evolution.”
Reference: “Running performance in Australopithecus afarensis” by Karl T. Bates, Sian McCormack, Evie Donald, Samuel Coatham, Charlotte A. Brassey, James Charles, Thomas O’Mahoney, Pasha A. van Bijlert and William I. Sellers, 18 December 2024, Current Biology.
DOI: 10.1016/j.cub.2024.11.025
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1 Comment
Apples and oranges compared nicely here. Comparing a presumptive being more or less typical for her branch of our species against elite modern human runners is not a fair comparison. Compare her with a young high school runner who competes but won’t compete once graduated.
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