In life, Lucy measured 1.10 meters tall, weighed about 27 kilosand had a skull comparable to that of a chimpanzee
The first digital reconstruction of the muscles of a hominin (primitive human) has shown that 3.2 million years ago, ‘Lucy’, the Australopithcus afarensis fossil revolutionized the study of human evolution she was already walking as upright as we were.
The research, led by Ashleigh Wiseman of the University of Cambridge, has modeled in 3D the muscles of the legs and the pelvis of the famous Lucy, discovered by Donald Johanson in Ethiopia in 1974.
Named after the Beatles’ hit (‘Lucy in the Sky with Diamonds’)is one of the most complete skeletons of Australopithecus, of which 40% of the bones are preserved.
In life, Lucy measured 1.10 meters tall, weighed about 27 kilos, and had a skull comparable to that of a chimpanzee and a brain equivalent to a third of ours. It is believed that he was in his 20s when he died, as his wisdom teeth had just come in.
Australopithecus afarensis were an early human species that lived in eastern Africa more than three million years ago and that it managed to adapt to the forests and the savannah, which allowed it to survive for almost a million years.
But their main trait is that they could do something that primates cannot do: walk on two legs
However, while paleoanthropologists agree that Lucy was bipedal, disagree on how he walkedand while some believe that it moved crouched down and that, like chimpanzees -our common ancestor- it could walk on two legs, others believe that it moved in a way more similar to our upright bipedalism.
in the last 20 years consensus has begun to be reached on walking fully upright, and Wiseman’s work corroborates this. Details of his research have been published in the Royal Society Open Science journal.
digital reconstruction
The study was made possible by the open publication of new data about Lucy, which allowed Wiseman’s team to create a digital model of the muscular structure of the hominin lower body.
To recreate Lucy’s muscles, Wiseman used MRIs and CT scans of the muscular and skeletal structures of a modern woman and man to trace “muscle trajectories” and build a digital musculoskeletal model.
He then used the virtual models of Lucy’s skeleton to “rearticulate” the joints, that is, recompose the skeleton and recreate its movements in life and, finally, compared them with the muscles of modern humans.
The team recreated 36 muscles in each legmost of them were much larger in Lucy and bulky than those of modern humans.
For example, the major muscles of Lucy’s calves and thighs were more than twice the size of those of modern humans, since we have a much higher fat to muscle ratio.
In fact, the muscles made up 74% of the total mass of Lucy’s thigh, compared to only 50% in humans.
Lucy’s knee extensor muscles, and the leverage they would allow, confirm the ability to straighten knee joints as much as a healthy person can today.
“Now we are the only animal that can stand upright with our knees straight but Lucy’s muscles suggest that it was as adept at bipedalism as we are, though possibly he felt at home in the trees as well. It is likely that he walked and moved in a way that we don’t see in any living species today,” Wiseman summarizes.
These reconstructions will help study mobility in humansand determine “what drove our evolution” and what capacities “we have lost”, concludes the researcher.