SCIENTISTS: LUCY SPENT MORE TIME IN TREES THAN PREVIOUSLY THOUGHT
Lucy climbed trees, walked with a wobbly gait and had stronger muscles than humans, according to a new analysis of our ancient ancestor’s fossilized remains.
The work, published Wednesday in PLOS One, is the first to mine the internal bone structure of the world’s most famous Australopithecus afarensis for information on how the petite hominid lived her life 3.18 million years ago.
“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 Christopher Ruff, a professor of functional anatomy and evolution at Johns Hopkins University School of Medicine, and the lead author on the study. “We’re saying she probably used trees on a daily basis.”
To come to this conclusion, the authors turned to a micro-CT scan of Lucy’s skeleton that was taken at the University of Texas, Austin in 2008. Lucy’s fossilized bones had been scanned not long after their discovery in the early 1970s, but the instruments back then were not powerful enough to show the internal structure of her bones.
“Lucy is a fully mineralized fossil, so she’s like a rock, and the problem with lower energy CT is that they can’t see through rock,” said John Kappelman, a UT professor of anthropology and geological sciences who did the recent scans. “Up until 2008, we had had no data at all on the internal structure of her bones. She was radiographically opaque.”
Being able to peer into the interior of Lucy’s bones has shed a whole new light on how Lucy lived her life, Ruff said.
Like our bones, Lucy’s bones respond to pressure. The more force exerted on them, the stronger they become.
For example, the bones in a professional tennis player’s playing arm can be 50 percent stronger than in the non-playing arm. The same is true for pitchers and their pitching arm.
“Bones adapt,” Ruff said. “With overuse you add more bone, with underuse you lose bone.”
Ruff and his team concentrated on cross-sectional scans of Lucy’s one remaining thigh bone and her two remaining upper arm bones. Particularly, they were looking for how tissue was distributed along the bone shaft as an indication of strength.
“It’s the same type of analysis that an engineer would use in designing a bridge,” Ruff said.
Next, the group compared the relative strength of Lucy’s bones to those from a database of more than 1,000 pre-20th-century humans and 100 chimpanzees.
Previous work on chimpanzees and gorillas revealed that measurements like these matched up with locomotion behavior. For example, animals that climbed trees had relatively stronger upper limbs compared with those that did not climb trees.
The authors found that Lucy’s upper limb strength was intermediate between humans and chimps, but a bit closer to the chimp side. This suggests that she used her upper limbs significantly more than we do, although not as much as chimpanzees, which frequently climb trees.