2023-06-14 07:00:02
‘Lucy’, the petite Australopithecus afarensis who lived more than 3 million years ago in what is now the Afar region of Ethiopia, is one of the most famous human ancestors. He was one meter tall and weighed just 28 kilos, he had the face of an ape and his brain was a third of ours, but he was already able to walk on two legs. Now, new research published in the journal ‘Royal Society Open Science’ has revealed that the hominid possessed a musculature that would be the envy of any gym user. Much bigger and more powerful than ours, she allowed her to stand upright like any of us.
Researcher Ashleigh Wiseman, from the University of Cambridge, has digitally reconstructed the missing soft tissue from Lucy’s lower body, something that has never been done before with an early human ancestor. She modeled the muscles of the legs and pelvis in 3D using scans of complete fossils of the hominin, of which 40% of its skeleton is preserved. To do this, she used recently published open source data.
Wiseman virtually reassembled the skeleton to define the axis from which each joint could move and rotate, replicating how it moved during the hominin’s lifetime. Finally, the muscles were layered on top, including a small discernible “muscle scar” (the traces of muscle connection detectable in the fossilized bones).
The research recreated 36 muscles in each leg, most of which were much larger in ‘Lucy’ and took up more space in her legs compared to modern humans. As the saying goes, he was really ‘ripped’.
For example, ‘Lucy’s’ major calf and thigh muscles were more than twice the size of those of modern humans, since we have a much higher fat-to-muscle ratio. The thigh muscles, a ‘rock’, made up 74% of the total mass, compared to only 50% in sapiens.
Paleoanthropologists agree that ‘Lucy’ was bipedal, but not how she walked. Some have argued that she moved in a crouching fashion, similar to chimpanzees, our common ancestor, when they walk on two legs. Others believe that her movement was closer to our own upright bipedalism, a theory that has gained traction in recent years.
Wiseman’s work adds further weight to this idea. ‘Lucy’s’ knee extensor muscles, and the leverage they would allow, confirm the ability to straighten the knee joints as much as a healthy person can today.
Complete views of the muscle modeling in ‘Lucy’, in which 36 muscles per lower limb were created. Shown in comparison to 3D human muscles that were segmented from MRI data
an original movement
“Lucy’s ability to walk upright can only be known by reconstructing the path and space a muscle occupies within the body,” says Wiseman. “Now we are the only animal that can stand upright with straight knees. ‘Lucy’s’ muscles suggest that she was as adept at bipedalism as we are, though she was possibly comfortable among the trees as well. She probably walked and moved in a way that we don’t see in any species alive today,” he says.
According to the researcher, these australopithecines would have roamed open wooded grassland areas, as well as denser forests in eastern Africa, around 3 to 4 million years ago. Reconstructions of ‘Lucy’s’ muscles suggest that it would have been able to “exploit both habitats effectively”.
Wiseman believes his reconstructions may help scientists understand how this human ancestor walked. “Muscle reconstructions have already been used to measure the running speed of a T-Rex, for example,” he says. “By applying similar techniques to ancient humans, we want to reveal the spectrum of physical movement that drove our evolution, including those capabilities we’ve lost,” he adds. All of this will serve to better understand what has often been called the ‘grandmother of humanity’.
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