Human ancestor Lucy's cause of death solved, scientists say

The famous human ancestor known as Lucy walked the Earth, but it was her tree climbing that might have led to her demise, a new study suggests.

An analysis of her partial skeleton reveals breaks in her right arm, left shoulder, right ankle and left knee injuries that researchers say resulted from falling from a high perch such as a tree.

Lucy likely died quickly, said John Kappelman, an anthropologist at the University of Texas at Austin, who published the findings Monday in the journal Nature.

"I don't think she suffered," Kappelman said.

But several other researchers, including Lucy's discoverer, disagree. They contend most of the cracks in Lucy's bones are well documented and came after her death from the fossilization process and natural forces such as erosion.

How Lucy met her end has remained a mystery since her well-preserved fossil remains were unearthed more than four decades ago. Her discovery was significant because it allowed scientists to establish that ancient human ancestors walked upright before evolving a big brain.

Lucy was a member of Australopithecus afarensis, an early human species that lived in Africa between about 4 million and 3 million years ago. The earliest humans climbed trees and walked on the ground. Lucy walked upright and occasionally used her long, dangling arms to climb trees. She was a young adult when she died.

Tim White, a paleoanthropologist at the University of California, Berkeley, called the study's conclusion a "misdiagnosis." The Texas researchers "appear to have focused only on the cracks that they could attribute to an imagined fall, ignoring the additional abundant cracks," White said in an email.

• New human ancestor lived alongside Lucy
• Humanity's ancestors walked 3 million years ago

The split highlights the difficulty of pinpointing a cause of death from fossilized remains. Scientists rarely know how early humans died because skeletons are incomplete and bones tend to get crushed under sand and rocks.

Over the years, Lucy's discoverer Donald Johanson has tried to solve the mystery.

Lucy's skeleton, which is 40 per cent complete, was recovered in Ethiopia in what was an ancient lake near fossilized remains of crocodiles, turtle eggs and crab claws.

"There's no definitive proof of how she died," said Johanson of Arizona State University.

No signs of healing

The Texas team examined Lucy's bones and used high-tech imaging. Kappelman said the scans revealed multiple broken bones and no signs of healing, suggesting the injuries occurred around the time of death.

He reconstructed her final moments: The 1.06-metre (3-foot-6-inch) Lucy fell from at least 12 metres (40 feet)and hit the ground at 56 kilometres per hour (35 miles per hour). She landed on her feet before twisting and falling. Such an impact would have caused internal organ damage. Fractures on her upper arms suggest she tried to break her fall.

Kappelman theorized that Lucy's walking ability may have caused her to be less adept at climbing trees, making her more vulnerable to falling from heights.

Not everyone agrees that her tree-climbing skills were lacking. Other scientists point out that there have been documented falls by chimpanzees and orangutans, which spend more time in trees than Lucy's species.

"Without a time machine, how can one know that she didn't just get unlucky and fall?" William Harcourt-Smith of the American Museum of Natural History said in an email.