Strong, Thick Arm Bones Hint Lucy The Australopithecus Climbed Trees Like Chimpanzees
Researchers who suggested that the 3.2-million-year-old human ancestor Lucy the Australopithecus died falling from a tree now claim that regardless of her capability to walk upright, she likely climbed trees regularly or even lived up there.
Clues From Lucy's Bones
In a new study published in the journal PLOS One, researchers looked at the internal bone structure of the most famous Australopithecus afarensis to know how the hominid lived.
Bone scans revealed that Lucy's arm bones are thicker and stronger compared with her thigh bones, a pattern more similar to what is seen in chimpanzees than in modern humans and other later human ancestors.
The evidence suggests that while Lucy was able to walk upright on the ground, it climbed, hung and swung in trees and she did this regularly.
"The limb bone structural proportions of A.L. 288-1 provide evidence for substantially more arboreal, i.e., climbing behavior than either modern humans or Homo erectus," the researchers wrote in their study.
"The frequency and magnitude of force required to stimulate bone modeling and remodeling of this kind implies that this behavior was adaptively significant and not a trivial component of the locomotor repertoire."
Scientists can determine which bones get used more by comparing the strength and thickness of the long arm bones relative to those of the long leg bones because the pull on the bones attached to heavily used muscles makes the bone stronger and thicker.
Modern humans spend little time in trees so their arm bones are weaker compared with their leg bones. The ratio is different in chimpanzees that swing, eat, sleep and seek shelter in trees.
Why Lucy Climbed Trees
Researchers said that their findings show Lucy stayed on trees regularly.
"Most people have agreed for a while that she did some tree climbing, or had done tree climbing in the recent past, but there were a lot of questions about whether it was a major part of her lifestyle," said study researcher Christopher Ruff, Johns Hopkins University School of Medicine. "We're saying she probably used trees on a daily basis."
Among the possible reasons why Lucy's kind may have used trees often include the need to escape from predators and to forage food.
Lucy is famous because she has the most complete hominid fossil ever found. The creature was just over 3.5 feet tall and had a brain slightly bigger than that of the modern-day chimpanzee.