Early human ancestors spent longer time on trees than thought

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Washington, October 26: Early human ancestors abandoned climbing behaviour much later than many researchers had previously suggested, according to a new study.

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 by Dr. Alemseged.

Further preparation and extensive analyses of these rare bones showed them to be quite apelike, 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. These remarkable fossils provide strong evidence that these individuals were still climbing at this stage in human evolution,” said Dr. Green.

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 Dr. Alemseged.

Selam was a three-year-old A. afarensis girl who lived about 3.3 million years ago, and she represents the most complete skeleton of her kind to date.

The analysis of the shape and function of the bones revealed that A. afarensis shoulder blades are apelike, indicating a partially arboreal lifestyle.

Drs. Green and Alemseged also found that, like living apes, the shoulder anatomy of juvenile and adult representatives of A. afarensis were quite similar.

“Human scapulae change shape throughout ontogeny in a significantly different manner than closely related apes,” said Dr. Green.

“When we compared Selam’s scapula with adult members of Australopithecus afarensis, it was clear that the pattern of growth was more consistent with that of apes than humans,” he explained.

At the same time, most researchers agree that many traits of the A. afarensis hip bone, lower limb, and foot are unequivocally humanlike and adapted for upright walking.

The new findings are published in the latest issue of the journal Science. (ANI)