Revolutionary Simulations Illuminate the Path of Human Evolution

The University of Liverpool has spearheaded an international consortium of researchers to reevaluate the locomotion abilities of Australopithecus afarensis, the early human progenitor famously epitomized by the fossil known as ‘Lucy’.

Karl Bates, Professor of Musculoskeletal Biology, gathered specialists from various institutions throughout the UK and the Netherlands. Together, they employed state-of-the-art computer simulations to reveal the running mechanics of this ancient species, utilizing a digital model of ‘Lucy’s’ skeleton.

Prior studies on the fossilized footprints of Australopithecus conducted by numerous research teams have indicated that Lucy likely walked quite upright and more similarly to a human rather than a chimpanzee. These latest discoveries indicate that Lucy’s overall bodily structure constrained running speed when compared to contemporary humans, thus supporting the notion that human physiology evolved in order to enhance running capability, with maximum speed being a more significant factor than previously believed.

Professor Bates stated: “When Lucy was unearthed 50 years ago, it was the most complete skeleton of an early human ancestor available. Lucy is an intriguing fossil because it encapsulates what one might consider an intermediate phase in the evolution of Homo sapiens. Lucy connects the divide between our tree-dwelling predecessors and modern humans, who efficiently navigate on two legs.

“By modeling running abilities in Australopithecus and contemporary humans, we have been able to explore queries regarding the evolution of running in our ancestors.
“For many years, scientists have engaged in discussions over whether a more efficient walking capability or enhanced running performance was the primary catalyst driving the evolution of numerous distinctly human traits, such as elongated legs, shorter arms, stronger leg bones, and arched feet. By demonstrating how Australopithecus walked and ran, we are starting to answer these queries.”

The team employed computer-based motion simulations to emulate the biomechanics and energetics of running in Australopithecus afarensis, alongside a model of a human. In both Australopithecus and human simulations, the team performed multiple simulations where various features believed to be crucial for modern human running, like larger leg muscles and an extended Achilles Tendon, were alternately included and excluded, thereby recreating evolutionary events digitally to observe how they impact running velocity and energy expenditure.

Muscles and other soft tissues do not fossilize, hence paleontologists are unaware of the size of ‘Lucy’s’ leg muscles or other vital metrics. Nevertheless, these innovative digital models varied muscle attributes from chimpanzee-like to human-like, yielding a spectrum of estimates for running speed and efficiency.

The simulations demonstrate that while Lucy could run upright on both legs, her top speeds were considerably slower than modern humans. Indeed, even the fastest speed predicted for Lucy (in a model with very human-like muscles) was notably modest at merely 11mph (18kph). This speed pales in comparison to top human sprinters, who achieve peak velocities exceeding 20mph (38kph). The models also indicate that the range of intermediate (‘jogging’) speeds that animals utilize for longer distances (‘endurance running’) was severely limited, possibly implying that Australopithecus did not partake in the extended hunting strategies considered essential for the earliest humans.

Professor Bates further remarked: “Our findings emphasize the significance of muscle structure and body ratios in the advancement of running skills. Skeletal robustness does not appear to have been a limiting factor, but evolutionary modifications to muscles and tendons contributed significantly to enhancing running speed and economy.

“As we commemorate the 50th anniversary of Lucy’s discovery, this research not only illuminates her abilities but also highlights the progress modern science has made in unraveling the narrative of human evolution.”

The research, ‘Running performance in Australopithecus afarensis,’ was published in Current Biology (DOI:10.1016/j.cub.2024.11.025).