Lucy’s Achilles Heel: Why our ancient ancestor couldn't keep up

A new study published in Current Biology provides insights into the running abilities of Lucy, the 3.2 million-year-old Australopithecus afarensis whose discovery in 1974 has captivated scientists and the public alike. According to research led by Karl T. Bates and his team at the University of Liverpool, Lucy could not have rivaled an average human in a race, as reported by Infobae.

Lucy, an early human ancestor who walked upright on two legs—a milestone in human evolution—had speed and energy efficiency limitations when it came to running. As reported by Live Science, recent findings suggest that while she was bipedal, her speed and energy efficiency were extremely limited, using up between 1.7 and 2.9 times more energy than modern humans to run at her maximum speed.

As reported by Infobae, the researchers employed musculoskeletal modeling techniques to reconstruct Lucy's skeletal and muscular anatomy. "Basically, we reconstructed a simplified digital 'robot' of A. afarensis, composed of all the main skeletal and muscular features that determine running speed," explained Bates, an evolutionary biomechanics researcher at the University of Liverpool.

Simulations revealed that Lucy's maximum running speed was around 18 km/h (approximately 11 mph), inferior to the average sprinting speed of modern humans at 22 km/h. Even when adjusted for differences in body size, the difference remained considerable.

In comparison, an average human athlete can run at a maximum speed of 8 meters per second (around 29 km/h), and the best sprinters, such as Usain Bolt, reach speeds over 43 km/h, demonstrating the difference in running abilities between modern humans and ancient ancestors like Lucy.

The study found that Lucy's physical features, including a wide torso, long arms, and relatively short legs, played a role in her limited running abilities. These proportions were not ideal for optimizing running.

Researchers paid particular attention to the Achilles tendon and calf muscles, which in modern humans work like a spring, accumulating and releasing energy during movement. In Lucy, the Achilles tendon was probably less developed and less elastic, reducing her running efficiency, as reported by Cursor Info.

"Key features in the human body plan evolved specifically for improved running performance," the researchers stated, as reported by Live Science, reminding us that our bodies today are the result of a long series of adjustments shaped by the challenges faced by our ancestors.

Even when the researchers modeled Lucy with human-like Achilles tendon and calf muscles, she was still slower, indicating that other factors contributed to her inefficiency. "Even if you jack up all the muscles, she was still slower," said Bates, as reported by Scientific American.

As reported by SciencePost, the analysis showed that running would have been taxing for Lucy, requiring her more energy than a modern human and suggesting that she would have exhausted her reserves if she had to run long distances. Running required Lucy 2.9 times more energy than it does a modern human, indicating low endurance.

These findings support the theory that adaptations for efficient running evolved later in the human lineage, particularly with Homo erectus, who had body proportions closer to modern humans and anatomical adaptations favoring running.

"The ability to run was central to the survival of our ancestors," noted the researchers, as reported by SciencePost. Running allowed them to hunt prey over long distances, escape predators, and cover territories in search of food.

"Understanding Lucy's physical limitations helps us better grasp the steps that led to the emergence of our current abilities," the researchers emphasized, as reported by SciencePost. Although Lucy was not an exceptional runner, she remains a piece of the evolutionary puzzle.

The research represents the first rigorous attempt to determine the running speed of Australopithecus afarensis. Digital simulations and 3D models offer a window into the past, allowing scientists to explore how these ancestors moved and survived.

This article was written in collaboration with generative AI company Alchemiq