'Lucy' was already walking as upright as us 3.2 million years ago

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 that revolutionized the study of human evolution, already walked as upright as we do.

The research, led by Ashleigh Wiseman, from the University of Cambridge, has modeled in 3D the muscles of the legs and pelvis of the famous Lucy, discovered by Donald Johanson in Ethiopia in 1974.

Named in honor of the Beatles' success (“Lucy in the Sky with Diamonds”), it is one of the most complete skeletons of Australopithecus, of which 40% of the bones are preserved.

In life, Lucy was 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 was an early human species that lived in eastern Africa more than three million years ago and managed to adapt to the forests and savannah, allowing it to survive for almost a million years.

But their main feature is that they could do something that primates cannot do: walk on two legs.

However, although paleoanthropologists agree that Lucy was bipedal, they disagree on how she walked, and while some believe that she moved in a crouching position and that, like chimpanzees -our common ancestor- she could walk on two legs, others believe that she moved in a bipedal way. more similar to our upright bipedalism.

A consensus on walking fully upright has begun to emerge in the last 20 years, and Wiseman's work bears this out. Details of their 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 on Lucy, which enabled 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.

Then, he used the virtual models of Lucy's skeleton to “rearticulate” the joints, that is, to recompose the skeleton and recreate its movements in life, and finally, he compared them with the muscles of modern humans.

The team recreated 36 muscles in each leg, most of which were much larger in Lucy and bulkier than those of modern humans.

For example, the major muscles in Lucy's calves and thighs were more than twice the size of those of modern humans, since we have a much higher ratio of fat to muscle.

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 the knee joints as much as a healthy person can today.

“We are now the only animal that can stand upright with our knees straight, but Lucy's muscles suggest that she was just as adept at bipedalism as we are, although she may have been at home in trees as well.. It is likely that it walked and moved in a way that we do not see in any living species today,” Wiseman summarizes.

These reconstructions will help to study mobility in humans, and determine “what drove our evolution” and what capabilities “we have lost”, concludes the researcher.