– Lucy, so­cial climber

The early ho­minin’s strong arms sug­gest a life lived aloft. APRIL REESE re­ports.

Cosmos - - Digest -

Lucy, the world’s most fa­mous early ho­minin, may have walked on two legs but she pre­ferred to climb among the trees, a re­cent study sug­gests.

In the decades since the 1974 dis­cov­ery of the 3.18-mil­lion-year-old

Aus­tralo­p­ithe­cus afaren­sis fos­sil, sci­en­tists have de­bated whether Lucy lived pri­mar­ily on the ground or in the trees.

Hop­ing to settle that de­bate, a team led by Christo­pher Ruff at Johns Hopkins Univer­sity in the US scanned Lucy’s arm and leg bones to cre­ate de­tailed 3-D mod­els of their struc­ture. Then the re­searchers com­pared the mod­els with bone scans of other early ho­minins, mod­ern hu­mans and mod­ern chim­panzees.

Lucy’s arm bones, it turns out, were much stronger than her leg bones, and the weaker struc­ture of the leg bones meant she prob­a­bly had a some­what awk­ward, in­ef­fi­cient gait com­pared to later ho­minins. It seems likely, then, that she lived a pri­mar­ily ar­bo­real life, re­ly­ing more on her arms to get around than her legs, the re­searchers con­clude.

“Al­though bipedal when on the ground, the limb bone struc­tural pro­por­tions of [Lucy] pro­vide ev­i­dence for sub­stan­tially more ar­bo­real, i.e. climb­ing be­hav­iour than ei­ther mod­ern hu­mans or Homo erec­tus,” the re­searchers write in the study, pub­lished in PLOS One in Novem­ber.

Stay­ing off the ground would have helped keep Lucy safe from preda­tors, but it also posed its own risks: an ear­lier study found that she died by fall­ing from a tree.

CREDIT: DAVE EINSEL / GETTY IM­AGES

Re­cent scans of Lucy’s skele­ton showed the bones of her arms were stonger than those of her legs – she was there­fore prob­a­bly a tree- dweller.

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