Scientists discover cause of death of oldest human ancestor

Over 40 years after paleoanthropologists discovered Lucy, one of the oldest hominin fossils ever found, new research suggests that our 3.18-million-year-old ancestor died after falling from a large height.

When Lucy’s skeleton was discovered in Ethiopia in 1974, it was found to be relatively complete, eventually allowing scientists to conclude that Lucy’s body was subjected to severe injury not long before her death, though her exact cause of death had since been up for debate. However, findings from scientists from the University of Texas at Austin suggest that skeletal fractures obtained by Lucy close to the time of her death are consistent with injuries sustained from a high fall, such as one from a tree.

“Lucy has been at the center of a vigorous debate about the role, if any, of arboreal locomotion in early human evolution,” stated the study’s abstract, referring to the physical traits of Lucy’s species Australopithecus afarensis. “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.”

Arboreal locomotion is the ability for animals to move within trees and is a trait whose role has long been debated to have played a part in early human evolution. This makes the paper’s point crucial in the argument for arboreal locomotion in early human development, with the finding implying that Lucy would have been capable of arboreal locomotion.

A research team, led by Dr. John Kappelman, professor of anthropology, first used computed tomographic scans to determine that Lucy’s bones had been fractured prior to her death. In total, more than 35,000 high-resolution images were generated, allowing the team to see details of the fracture that had previously been undiscovered. Lucy’s upper right arm bone was fractured, but was discovered to contain bits of bones held in place by soft tissue. In the case of a body buried and compressed by sediment, these bits of bone are typically scattered, but the contrary condition of Lucy’s bone implies that the fracture was obtained prior to death and not years after.

Other damaged bones from Lucy’s skeleton were analyzed the same way and their conditions were found to be consistent with that of her upper right arm bone. The right humerus was also broken in several places, along with Lucy’s shoulder blade.

The study concluded that Lucy’s injury was the result of “an impact following a vertical deceleration event when an accident victim consciously stretches out their arm in an attempt to break their fall. Compressive contact between the hand and the ground impacts the humeral articular head against the glenoid [part of the shoulder blade].”

The pattern of the fractures also indicated that the injuries occurred while Lucy was still alive, but she did not live long after the event, as evidenced by the fact that her bones showed no healing.

The team compared their findings to similar scans of patients from hospital emergency rooms in order to come to their conclusion. Based on her estimated height and weight, Lucy most likely had to fall from a large distance in order to suffer the injuries to her bones. She began her fatal fall feet first, eventually landing on her heels and extending her arms out in order to brace herself for impact, thus resulting in the injuries to her arms.

Lucy’s skeleton was found in what is now the village of Hadar, Ethiopia, an area known for its relative abundance of fossils. In addition to being a fossil site, the area is also known for once being a grassy woodland area populated by many trees. This is consistent with the paper’s theory that Lucy fell from a tree.

If Lucy really fell from a tree, this would disprove the theory that A. afarensis was a completely terrestrial species of hominin. Due to her small stature, the paper reasons that Lucy took to the trees at night in order to protect herself and search for sustenance.

“This paper is wonderful: It forces us to put Lucy in context,” said Daniel Lieberman, paleoanthropologist at Harvard University. “It’s our job as scientists to be skeptical but they’ve made a very compelling case.”

According to the study, primates and some modern humans use trees to forage for food, while also suffering great injuries or fatalities due to their exploits. Indeed, the case for our ancestors being able to move on both land and through trees has been made stronger due to this study.