Early human ancestors spent longer time on trees than thought

Early human ancestors spent longer time on trees than previously thought, remaining very active climbers till much later, a new study has found.

Despite the ability to walk upright, early human ancestors represented by the famed "Lucy" fossil spent much of their time on trees, researchers say.

The discovery appears to have finally ended the debate over whether this bipedal hominid still continued to climb trees, much like their earlier ape ancestors.

Australopithecus afarensis (the species of the well-known "Lucy" skeleton) was an upright walking species, but the question of whether it also spent much of its time in trees has been the subject of much debate, partly because a complete set of A afarensis shoulder blades has never before been available for study.

For the first time, Midwestern University Professor David Green and Curator of Anthropology at the California Academy of Sciences, Zeresenay Alemseged, have thoroughly examined the two complete shoulder blades of the fossil "Selam," an exceptionally well-preserved skeleton of an A afarensis child from Dikika, Ethiopia, discovered in 2000.

Further preparation and extensive analyses of these rare bones showed them to be quite ape-like, suggesting that this species was adapted to climbing trees in addition to walking bipedally when on the ground.

"The question as to whether Australopithecus afarensis was strictly bipedal or if they also climbed trees has been intensely debated for more than thirty years," said Green.
"These remarkable fossils provide strong evidence that these individuals were still climbing at this stage in human evolution," he said.

Dr Alemseged, assisted by Kenyan lab technician Christopher Kiarie, spent 11 years carefully extracting the two shoulder blades from the rest of the skeleton, which was encased in a sandstone block.

"This study moves us a step closer toward answering the question 'When did our ancestors abandon climbing behaviour?' It appears that this happened much later than many researchers have previously suggested," said Alemseged.

Researchers found that these bones had several details in common with those of modern apes, suggesting they lived part of the time in trees.

For instance, the socket for the shoulder joint was pointed upward in both Selam and today's apes, a sign of an active climber. In humans, these sockets face out to the sides.
The new findings are published in the journal Science.