Family tree fall: human ancestor Lucy died in arboreal accident, say scientists

Extract from The Guardian

Researchers claim analysis of 3.2m-year-old skeleton of ‘grandmother of humanity’ shows injuries consistent with those of humans falling on hard ground, but others query findings

Branching off … a still from a reconstruction video of human ancestor Lucy the ape falling from tree to sustain injuries. Photograph: John Kappelman/University of Texas at Austin

Ian Sample Science editor

@iansample

Tuesday 30 August 2016 01.00 AEST 

The ancient human ancestor known as Lucy may have met her death more than 3m years ago when she tumbled out of a tree and crashed to the woodland floor, a team of US researchers claim.
A fresh analysis of the “grandmother of humanity” points out a number of cracks in the fossil bones that the scientists say match traumatic fractures seen in humans who suffer serious injuries from high falls on to hard ground.
“The consistency of the pattern of fractures with what we see in fall victims leads us to propose that it was a fall that was responsible for Lucy’s death,” said John Kappelman, an anthropologist who led the study at the University of Texas in Austin. “I think the injuries were so severe that she probably died very rapidly after the fall.”

A hypothetical scenario for Lucy’s fall out of a tall tree and the subsequent vertical deceleration based on the patterning of bone fractures. The first segment depicts about the last half of the fall from 7.4 m with a real time duration of 0.45 seconds. The second segment shows a close-up of the last 2.2 m of the fall. The third segment shows as low-motion (about 1/5 speed) close-up of the last 1.7 m of the fall. The last frame illustrates the fractures. Credit: John Kappelman, University of Texas at Austin

But the claims, published in the prestigious journal Nature, were roundly dismissed by scientists who spoke to the Guardian. They point out that a lot can happen to a skeleton in 3.2m years. Lucy’s body may have been trampled by stampeding beasts before sediment covered the bones and gradually encased them in rock.
“There is a myriad of explanations for bone breakage,” said Donald Johanson at Arizona State University, who discovered Lucy more than 40 years ago in the Afar region of Ethiopia. “The suggestion that she fell out of a tree is largely a “just-so story” that is neither verifiable nor falsifiable, and therefore unprovable.”
Tim White, a paleoanthropologist at the University of California in Berkeley, said the cracks were no more than routine fossil damage. “If paleontologists were to apply the same logic and assertion to the many mammals whose fossilised bones have been distorted by geological forces, we would have everything from gazelles to hippos, rhinos, and elephants climbing and falling from high trees,” he said.
Lucy was discovered in 1974 when Johanson and his student, Tom Gray, were searching for ancient animal bones on the parched terrain near the village of Hadar in northern Ethiopia. The chance finding of a piece of arm bone led them to uncover more remains of an ape-like animal. Eventually, they gathered about 40% of the skeleton.
That evening as the team celebrated at camp the Beatles song Lucy in the Sky with Diamonds came on providing the scientists with a name for their discovery. The species, Australopithecus afarensis, meaning “southern Ape from Afar”, walked upright, but had long, strong arms and curved fingers, making Lucy more adept at life in the trees than modern humans.
Kappelman became intrigued by some of the cracks in Lucy’s bones after examining high resolution x-ray scans of the fossils. The cracks had been described before and put down to natural processes such as erosion and fossilisation. But Kappelman thought there might be another explanation.
Working with Stephen Pearce, an orthopaedic surgeon, the scientists identified cracks in more than a dozen bones, ranging from the skull and spine to the ankles, shins, knees and pelvis, which look like compressive fractures sustained in a fall. One injury to the right shoulder matches the kind of fracture seen when people instinctively put their arms out to save themselves, the scientists believe. Kappelman calls it “a unique signature” for a fall and evidence that the individual was conscious at the time.

3D printouts of Lucy’s right humerus reconstructed Photograph: John Kappelman/University of Texas at Austin

From the scientists’ calculations, Lucy, who weighed less than 30kg, could have suffered similar injuries in a fall from about 15 metres. If Australopithecus afarensis climbed trees to nest, the animals could have spent hours a day at this or even greater heights. “We know that chimps fall out of trees and often it’s because they step on a branch that turns out to be rotten, and boom, down they come,” said Kappelman.
“Based on clinical literature these are severe trauma events. We have not been able to come up with a reasonable way that these could be fractured postmortem with the bones lying on the surface or even if the dead body was being trampled on. If somebody is trampled on the bone breaks in a different way. It doesn’t break compressively,” said Kappelman.
But Johanson is not impressed. The cracks on Lucy’s bones are similar to the damage seen on other early human and ancient mammal fossils throughout Africa and the rest of the world, he said. “We don’t know how long the fossilisation process takes, but the enormous set of forces placed on the bones during the build up of sediments covering the bones is a significant factor in promoting damage and breakage,” he added.

One of White’s major complaints is that the scientists fail to prove beyond doubt that the cracks in Lucy’s bones occurred around the time of death. “Such defects created by natural geological forces of sediment pressure and mineral growth are very common in fossil assemblages. They often confuse clinicians and amateurs who imagine them to have happened around the time of death,” White said. “Every single element of the Lucy fossil has cracks. The authors cherry pick the ones that they imagine to be evidence of a fall from a tree, leaving the others unexplained and unexamined.”
Kappelman concedes that we can never know for sure what happened. “None of us were there. We didn’t see Lucy die,” he said. “Thinking about testing this idea, it’s hard to get someone to fall out of a tree, but we have tests going on every single day in every emergency room on planet Earth when people walk in with fractures from falls,” he said.
In pondering Lucy’s death, she came back to life, Kappelman added. For the first time she became a living, breathing individual, because I could understand what I propose to be her death. We have all fallen down. For an instant in time you can identify with her and imagine exactly what this individual, who lived over 3m years ago, was doing at that instant.”