Study Suggests 3.2 Million-Year-Old Lucy Spent a Lot of Time in Trees

By Joanna Klein

Lucy was a small one. She weighed about as much as the average 2nd grader and stood about three-and-a-half feet tall. But that lady (or pre-lady, because Australopithecus afarensis like her weren’t quite human) was strong. Her famous skeleton, a 3.18 million-year-old fossil also known as AL 288-1, tells us so. But to build arm bones as strong as hers, she, and possibly other members of her species, probably spent a lot of time in trees, suggests a study published Wednesday in the journal PLOS One.

Lucy, discovered almost half a century ago, was the most complete skeleton of the earliest hominid ever found at the time. She changed our understanding of human evolution. There’s little doubt Lucy walked on two feet like a modern human, or that she climbed trees to sleep, avoid predators or gather food. Some scientists — including some involved in this study — even think she died after a fall from one. But just how much time she spent in trees has been a subject of contention because interpretations of her ancient skeletal clues are hard to prove. For the latest study, researchers looked at the ways bones can grow stronger or weaker with everyday use. And by examining the internal structure of Lucy’s upper right arm and leg bones and comparing them with the bones of around 100 chimpanzees and 1,000 modern humans, they concluded that climbing trees wasn’t just some trivial task. Lucy did it enough that the ratio of strength between her arms and legs is slightly more chimpish than human.

“That doesn’t mean she was acting like a chimp, just that she was stressing her limbs more like a chimpanzee than a modern human,” said Christopher Ruff, a paleoanthropologist at Johns Hopkins University who led the study.

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