paleoanthropology

On the fate of “Lucy,” our hominin relative

Everyone’s favorite Australopithecus afarensis “Lucy” is at the center of a debate regarding the circumstances of her death.

New research from the University of Texas at Austin proposes that Lucy’s cause of death was a fall out of a tall tree, based on CT scan analyses of multiple fractures in her bones.

Lucy (the common name of specimen AL 288-1) was first discovered in 1974 at the Hadar site in the Afar region of Ethiopia. She has been dated to ~3.18 million years old. 40% of her skeleton was recovered, which makes her one of the oldest and most complete hominin specimens ever found.

Lucy’s skeleton, like most all other fossils, has experienced damage in the 3 million plus years since she was buried. CT scans that the University of Texas team conducted of Lucy skeleton largely concurs with the original description of the skeleton’s post-mortem damage; however, they differ in their interpretations of the causes.

The University of Texas team propose that a portion of Lucy’s fractures are actually perimortem—meaning they occurred at or near the time of death. They described what they believe to be ‘greenstick’ fractures, when a bone partially bends and breaks like a twig. Based on clinical comparisons, fractures like these would be produced by a “vertical deceleration event” and not by fossilization processes.

The team thus concluded that Lucy died from a fall out of a tall tree. Since Lucy’s species A. afarensis walked on two legs at this time (i.e. were bipedal), they inferred that that adaptations that facilitated bipedality compromised their ability to safely climb in trees.

However, William Kimbel—the director of the Institute of Human Origins at Arizona State University—has worked in the Afar region for many years and disagrees with this interpretation. He has been quoted to say, “I think the methodology falls short of providing a realistic explanation for the majority of breaks in Lucy’s bones. We see this kind of damage frequently in a wide variety of animals that did not fall from trees. The authors did not go through the detailed, formal evaulation of alternative explanations of the breaks,”

Additionally, Donald Johanson, who was a member of the team that originally discovered Lucy, shares Kimbel’s sentiments. He was quoted to say, “Terrestrial animals like antelopes and gazelles, elephants and rhinos and giraffes—all these bones show very similar fracture and breakage patterns as Lucy. You can be sure they didn’t fall out of trees.”

So while the University of Texas team produce a compelling story about Lucy’s last moments, it is at this time nothing more than a story. It may well be impossible to concretely discern the cause of Lucy’s death, but interest in the matter will certainly be renewed.

Left image by author, right image of Lucy cast from Arizona State University’s Institute of Human Origins [x] | Kimbel’s quotation [x], Johansonn’s quotation [x] | Nature article about Lucy’s death [x]

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