Lucy, an Australopithecus Afarensis that lived three million years ago
Our bodies propel us forward at impressive speeds, with our muscles and tendons playing a vital role. But there was a time in our past when the first members of our family tree weren’t that fast.
About 3.2 million years ago, a hominin known as Australopithecus afarensis lived in East Africa. In 1974, the fossils of one of its most famous members, Lucy, were found in Ethiopia, an important discovery that allowed us to learn a little more about how our relatives moved and stood upright.
According to , Lucy’s skeleton showed that her species could walk upright on two legs, but her proportions and muscular arrangement were very different of current humans.
After studying her structure using 3D computer simulations, researchers concluded that Lucy could run on two legs, but will never have been able to match the speeds that, so naturally, modern humans can achieve.
“Lucy’s maximum running speed was considerably lower to that of our human model” – approximately 18 km/h. For reference, Usain Bolt’s top speed is over 27 mph (43 km/h) and a recreational runner’s top running speed is about 14 mph (22 km/h).
Furthermore, the investigation revealed that Lucy used among 1.7 and 2.9 times more energy than modern humans to run that fast, which suggests that she would have required significantly more energy to run a given distance than a modern human.
Australopithecines like Lucy had large upper bodies, long arms and short legswhich likely limited his running speed. Still, scientists have discovered that another reason that could explain Lucy’s slow and inefficient running may have been a Achilles tendon and triceps surae with different shapesa group of muscles in the calf (or calf).
We modern humans have a long, elastic Achilles tendon that connects our calf and ankle muscles to our heel bone. This anatomical arrangement allows us to have a powerful and efficient ankle, which is extremely important for high performance in running.
When the team modeled Lucy’s movement with human-like Achilles tendon and calf muscles, she proved to be even slower. The differences were mainly due to their smaller body size.
“This context emphasizes the crucial role of the Achilles tendon and triceps surae architecture in the evolution of hominin running energetics”, wrote the scientists, in the published in Current Biology. “Key features in the human body plan evolved specifically to improve running performance.”
