“Why Our Early Ancestors Stumbled: The Surprising Truth Behind Lucy’s Running Struggles”

A recent investigation analyzes the running abilities of Australopithecus afarensis, the species of the famous fossil “Lucy,” who existed more than 3 million years ago in East Africa. The results, published in Current Biology, utilize advanced 3D modeling techniques along with musculoskeletal simulations to examine the movement of Lucy’s body, revealing essential insights into the evolution of human running.

Lucy’s skeleton has been a focal point in understanding bipedalism in early hominins. Although she and her counterparts were capable of upright walking, their running abilities were significantly inferior to those of contemporary humans. As noted by Karl Bates, an evolutionary biomechanics specialist at the University of Liverpool and one of the study’s co-authors, “Even if you engage all the muscles, she was still slower.”

Related: Research shows Lucy and early hominins might have utilized tools 3.2 million years ago.

Simulations based on the fossilized remains of Lucy indicated that her maximum speed was about 11 mph (5 m/s), which is considerably slower than modern humans, whose sprinting velocities often exceed 18 mph (8 m/s) and can peak over 27 mph in exceptional athletes such as Usain Bolt. Additionally, running demanded 1.7 to 2.9 times more energy from Lucy than it does for a modern human, rendering her movement far less efficient.

Video illustrating the optimal maximal-speed running gait (4.26 m/s) for the Au. afarensis
model variation featuring modern human-like triceps surae architecture and muscle mass.
Credit: K. T. Bates et al., Current Biology (2024)

The research attributes Lucy’s slower pace and higher energy expenditure chiefly to her anatomical proportions and muscle structure. With elongated arms, a smaller physique, and a differently shaped Achilles tendon, Lucy lacked the spring-like mechanics that modern humans have for effective running. In contrast, modern humans benefit from a more elastic Achilles tendon along with shorter muscle fibers, which facilitate efficient energy storage and release during running, lowering the effort required to move forward.

The Achilles tendon and surrounding calf muscles—collectively termed the triceps surae—are crucial for contemporary running performance. These adaptations allow for both speed and endurance, characteristics missing in A. afarensis. Even when researchers modeled Lucy with human-like muscle arrangements, her running remained slower, further highlighting the effects of her smaller size and distinctive skeletal configuration.

The results underscore that the attributes allowing modern humans to excel in running did not simply arise as a byproduct of bipedal locomotion but necessitated specific evolutionary adaptations. Bates and his associates contend that changes in body proportions, especially the evolution of longer legs and more effective ankle structures, were vital for enhanced running performance. These adaptations likely transpired with the emergence of the genus Homo, around 2 million years ago, as early humans adjusted to novel environments and challenges.

Running presented considerable advantages to our ancestors, ranging from pursuing prey over vast distances to evading predators and exploring fresh territories. However, Lucy’s less efficient running implies that her species mostly depended on alternative survival strategies, such as climbing or gathering food within limited ranges.

While this study provides groundbreaking insights into Lucy’s running capabilities, the researchers intend to broaden their inquiry to encompass factors such as fatigue, bone strain, and upper body dynamics. These additional elements could yield further clarity on the evolutionary shift from the upright walking of early hominins to the running abilities mirrored in modern humans.

Lucy’s narrative serves as a reminder that human evolution was a gradual journey, defined by subtle yet significant modifications over millions of years.