Monday, 29 August 2016

"Lucy's" Fall Reconstructed

Lucy's fall
Perimortem fractures in Lucy suggest mortality from fall out of tall tree | Nature.

About 3 million years ago a creature midway between a chimpanzee-like ape and a human being fell out of a tree and died of her injuries.

This creature was the best known of some 300 specimens of a species now known to science as Australopithecus afarensis, a species which is one of the candidates for being the direct ancestor of the Homo genus. She is known to the worlds as 'Lucy'.

We've all fallen, and we know at that instant in time what she was trying to do,” he says. “We can actually fully identify with her at that moment, and I just felt a wave of empathy that I've never felt before with any of the other fossils that I've ever studied. My mind just jumped to seeing this little broken form, bleeding out, lying at the foot of a tree.

John Kappelman, project lead.
Lucy was about 3.5 feet tall, weighed about 60 pounds and, judging by her curved fingers, was a member of a species which probably still foraged in trees or took to them for safety. But she was also a member of a species which, judging by her pelvic girdle, lower limb and feet, spent a great deal of their time on the ground walking upright. The latter would have compromised her arboreal dexterity having lost the ability to grip effectively with her toes, unlike her more chimpanzee-like ancestors.

Now scientists believe they have pieced together her last few seconds of life as she fell from some 40 feet, probably out of a tree, hitting the ground at about 35 miles an hour, landing on her feet and falling forward onto outstretched arms.

The fractures in her arms, legs, ribs and skull all point to being perimortal. The investigation was carried out by a team led by John Kappelman, an anthropologist at the University of Texas at Austin, using a powerful form of CT scanning known as High-Resolution X-ray Computed Tomography Facility.

Abstract
The Pliocene fossil ‘Lucy’ (Australopithecus afarensis) was discovered in the Afar region of Ethiopia in 1974 and is among the oldest and most complete fossil hominin skeletons discovered. Here we propose, on the basis of close study of her skeleton, that her cause of death was a vertical deceleration event or impact following a fall from considerable height that produced compressive and hinge (greenstick) fractures in multiple skeletal elements. Impacts that are so severe as to cause concomitant fractures usually also damage internal organs; together, these injuries are hypothesized to have caused her death. Lucy has been at the centre of a vigorous debate about the role, if any, of arboreal locomotion in early human evolution. It is therefore ironic that her death can be attributed to injuries resulting from a fall, probably out of a tall tree, thus offering unusual evidence for the presence of arborealism in this species.

John Kappelman, Richard A. Ketcham, Stephen Pearce, Lawrence Todd, Wiley Akins, Matthew W. Colbert, Mulugeta Feseha, Jessica A. Maisano & Adrienne Witzel
Perimortem fractures in Lucy suggest mortality from fall out of tall tree
Nature (2016)
doi:10.1038/nature19332

Copyright © 2016, Rights Managed by Nature Publishing Group. Reprinted with kind permission under licence #3938340163795.

The authors also include a video reconstruction of the fall together with the points at which these injuries ocurred as she landed and fell forward.

Lucy is, of course still hotly debated by anthropologists about to what extent the species lived on the ground and how much time they spent in trees. This disagreement is just what we would expect of a species which was almost certain in transition between being mainly arboreal and mainly terrestrial.

Lucy and the several hundreds of fossils of her species show a distinctive skeleton adapted for both efficient bipedal walking and climbing trees but the entire combination so beautifully illustrated by Lucy's skeleton is the effectiveness of her species walking and climbing.

Based on the fossil hominin record between 6 million and 2 million years ago, this combination was successful for a very long time, and so I'm not convinced that Lucy's fatal fall is evidence that the success of life on the ground necessarily compromised the survival benefit—and thus the effectiveness—of climbing in Lucy's species.

Rick Potts, director of Smithsonian's Human Origins Program, quoted in SmithsonianMag.

So, while creationists are getting the panties in a wad over whether Lucy was a chimpanzee with human legs, whether Lucy actually existed or is variably a fake, a composite of several fossils from unrelated species, or even a creation of Satan made to mislead us, real scientists are using science to reconstruct her probable last few seconds of life. Meanwhile the serious scientific debate is not about whether she should be in our family tree but where exactly, and where her species should be positioned along a possible continuum between Au. afarensis and Homo erectus.

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