Human Ancestor 'Lucy' Mostly Climbed Trees Than Walked

A team of scientists from John Hopkins Medicine and the University of Texas Austin has determined that Lucy, the 3-million-year-old human ancestor discovered 42 years ago, was mostly a tree climber rather than a ground walker.

The study entitled "Limb Bone Structural Proportions and Locomotor Behavior in A.L. 288-1 ('Lucy')," published in the journal PLOS ONE, analyzed special CT scans of Lucy, discovering evidence that the infamous female hominin spent most of her time in trees.

The proof was in Lucy's internal bone structure. The researchers saw that the hominin's upper limbs were heavily built. Lucy's limbs was akin to tree-climbing chimpanzees, which meant that she used her arms to pull herself up to reach trees. In addition to her limbs were her foot, which scientists noted were structured to better adapt bipedal locomotion. This means that while climbing and grasping trees, Lucy mainly used her arms than her feet.

"We were able to undertake this study thanks to the relative completeness of Lucy's skeleton. Our analysis required well-preserved upper and lower limb bones from the same individual, something very rare in the fossil record," said Christopher Ruff, Ph.D., a professor of functional anatomy and evolution at the Johns Hopkins University School of Medicine, via Science Daily.

Lucy, a 3.18-million-year-old Australopithecus afarensis, was discovered 42 years ago in 1974 by Donald Johanson, an anthropologist from the Arizona State Universitym and graduate student Tom Gray. The two unearthed Lucy in the Afar region of Ethiopia and was considered as one of the oldest and most complete ancestors.

"Our results show that the upper limbs of chimpanzees are relatively more heavily built because they use their arms for climbing, with the reverse seen in humans, who spend more time walking and have more heavily built lower limbs. The results for Lucy are convincing and intuitive," Ruff said.

"It may seem unique from our perspective that early hominins like Lucy combined walking on the ground on two legs with a significant amount of tree climbing but Lucy didn't know she was "unique" -- she moved on the ground and climbed in trees, nesting and foraging there, until her life was likely cut short by a fall -- probably out of a tree," John Kappelman, Ph.D., anthropology and geological sciences professor, added.