![Cross-Section of Polygonal Muscle Modeling Approach](https://scitechdaily.com/images/Cross-Section-Polygonal-Muscle-Modeling-Approach-777x680.jpg 777w,https://scitechdaily.com/images/Cross-Section-Polygonal-Muscle-Modeling-Approach-400x350.jpg 400w,https://scitechdaily.com/images/Cross-Section-Polygonal-Muscle-Modeling-Approach-768x672.jpg 768w,https://scitechdaily.com/images/Cross-Section-Polygonal-Muscle-Modeling-Approach.jpg 1500w)
A cross-section of the polygonal muscle modeling approach, guided by muscle scarring and MRI data. Credit: Dr. Ashleigh Wiseman
Digital modeling of the legendary fossil’s soft tissue suggests that Australopithecus afarensis had strong leg and pelvic muscles suited to tree-dwelling, but knee muscles that allowed for fully upright walking.
A Cambridge University researcher has digitally reconstructed the missing soft tissue of an ancient human ancestor – or hominin – for the first time, revealing the ability to stand as upright as we do today.
“Lucy’s muscles indicate that she is as good at bipedalism as we are.” — Dr. Ashleigh Wiseman
Dr. Ashleigh Wiseman has a 3D model of hominin leg and pelvis muscles Australopithecus afarensis using scans of ‘Lucy’: the famous fossil specimen discovered in Ethiopia in the mid-1970s.
Australopithecus afarensis was an ancient man[{” attribute=””>species that lived in East Africa over three million years ago. Shorter than us, with an ape-like face and smaller brain, but able to walk on two legs, it adapted to both tree and savannah dwelling – helping the species survive for almost a million years.
Named for the Beatles classic ‘Lucy in the Sky with Diamonds’, Lucy is one of the most complete examples to be unearthed of any type of Australopithecus – with 40% of her skeleton recovered.
![Lucy 3D Muscle Model](https://scitechdaily.com/images/Lucy-3D-Muscle-Model-777x777.jpg 777w,https://scitechdaily.com/images/Lucy-3D-Muscle-Model-400x400.jpg 400w,https://scitechdaily.com/images/Lucy-3D-Muscle-Model-150x150.jpg 150w,https://scitechdaily.com/images/Lucy-3D-Muscle-Model-768x768.jpg 768w,https://scitechdaily.com/images/Lucy-3D-Muscle-Model-120x120.jpg 120w,https://scitechdaily.com/images/Lucy-3D-Muscle-Model.jpg 1200w)
A digitization of the muscle attachment areas used to build the model of Lucy’s muscles, next to the completed 3D muscle model. Credit: Dr. Ashleigh Wiseman
Wiseman was able to use recently published open-source data on the Lucy fossil to create a digital model of the 3.2 million-year-old hominin’s lower body muscle structure. The study is published in the journal Royal Society Open Science.
The research recreated 36 muscles in each leg, most of which were much larger in Lucy and occupied greater space in the legs compared to modern humans.
For example, major muscles in Lucy’s calves and thighs were over twice the size of those in modern humans, as we have a much higher fat-to-muscle ratio. Muscles made up 74% of the total mass in Lucy’s thigh, compared to just 50% in humans.
A 3D polygonal model, guided by imaging scan data and muscle scarring, reconstructing the lower limb muscles of the Australopithecus afarensis fossil AL 288-1, known as ‘Lucy’. In this model, muscles are color coded. Credit: Dr. Ashleigh Wiseman
Paleoanthropologists agree that Lucy was bipedal, but disagree on how she walked. Some have argued that he moved in a crouching waddle, similar to chimpanzees – our common ancestor – when they walk on two legs. Others believe that his movement is closer to our own upright bipedalism.
Research over the last 20 years has seen a consensus begin to emerge for fully upright walking, and Wiseman’s work adds further weight to it. Lucy’s knee extensor muscles, and the leverage they will allow, demonstrate the ability to straighten the knee joints as much as a healthy person can today.
“Lucy’s ability to walk upright can only be known by reconstructing the path and space occupied by the muscle within the body,” said Wiseman, from Cambridge University’s McDonald Institute for Archaeological Research.
![AL 288-1 vs Human Muscle](https://scitechdaily.com/images/AL-288-1-vs-Human-Muscles-777x899.jpg 777w,https://scitechdaily.com/images/AL-288-1-vs-Human-Muscles-346x400.jpg 346w,https://scitechdaily.com/images/AL-288-1-vs-Human-Muscles-768x889.jpg 768w,https://scitechdaily.com/images/AL-288-1-vs-Human-Muscles-1327x1536.jpg 1327w,https://scitechdaily.com/images/AL-288-1-vs-Human-Muscles-1769x2048.jpg 1769w,https://scitechdaily.com/images/AL-288-1-vs-Human-Muscles.jpg 2024w)
Completed views (ventral, dorsal, lateral and medial) of the polygonal muscle modeling approach in AL 288-1, where 36 muscles were created in each lower limb. Polygonal muscles of AL 288-1 are shown compared to 3D human muscles segmented from MRI scan data. Credit: Dr. Ashleigh Wiseman
“We are now the only animal that can stand upright with straight knees. Lucy’s muscles suggest she’s as good at bipedalism as we are, while possibly also being at home in trees. “Lucy probably walked and moved in a way that we don’t see in any living species today,” Wiseman said.
“Australopithecus afarensis would have roamed areas of open wooded grassland as well as denser forests in East Africa about 3 to 4 million years ago. These changes in Lucy’s muscles suggest that she can effectively exploit both habitats.”
Lucy is a young adult, standing at just over a meter tall and probably weighing around 28kg. Lucy’s brain is about a third the size of ours.
To recreate these hominin muscles, Wiseman started with some living humans. Using MRI and CT scans of the muscle and bone structures of a modern woman and man, he was able to map “muscle pathways” and build a digital musculoskeletal model.
A 3D polygonal model, guided by imaging scan data and muscle scarring, reconstructing the lower limb muscles of the Australopithecus afarensis fossil AL 288-1, known as ‘Lucy’. Credit: Dr. Ashleigh Wiseman
Wiseman then used existing virtual models of Lucy’s skeleton to “rearticulate” the joints – that is, put the skeleton together. This work determined the axis along which each joint was able to move and rotate, simulating how they move during life.
Finally, muscles are overlaid on top, based on paths from modern human muscle maps, as well as what small “muscle scars” are visible (the traces of muscle connection seen in fossilized bones). “Without open access to science, this research would not be possible,” Wiseman said.
These reconstructions can now help scientists understand how the human ancestor walked. “Muscle reconstructions have been used to measure the running speed of a T-Rex, for example,” Wiseman said. “By applying similar techniques to ancestral humans, we want to reveal the spectrum of physical movement that drove our evolution – including the abilities we’ve lost.”
Reference: “Three-dimensional volumetric muscle reconstruction of Australopithecus afarensis pelvis and limb, with estimates of limb leverage” by Ashleigh LA Wiseman, 14 Jun 2023, Royal Society Open Science.
DOI: 10.1098/rsos.230356