Early humans and apes likely evolved free-moving shoulders and flexible elbows to slow their descent from trees as gravity pulled on their heavier bodies, acording to new research. When early humans left forests for the grassy savanna, their versatile appendages were essential for gathering food and deploying tools for hunting and defense.
“The forelimbs of hominoid primates (apes) are decidedly more flexible than those of monkeys, especially at the shoulder, elbow and wrist joints,” said Dartmouth College graduate student Luke Fannin and colleagues.
“It is tempting to link the greater mobility of these joints to the functional demands of vertical climbing and below-branch suspension, but field-based kinematic studies have found few differences between chimpanzees and monkeys when comparing forelimb excursion angles during vertical ascent (upclimbing).”
“There is, however, a strong theoretical argument for focusing instead on vertical descent (downclimbing), which motivated us to quantify the effects of climbing directionality on the forelimb kinematics of wild chimpanzees (Pan troglodytes) and sooty mangabeys (Cercocebus atys).”
In the study, the authors used sports-analysis and statistical software to compare videos and still-frames they took of chimpanzees and sooty mangabeys climbing in the wild.
They also studied the anatomical structure of chimp and mangabey arms using skeletal collections.
They found that chimps and mangabeys scaled trees similarly, with shoulders and elbows mostly bent close to the body.
When climbing down, however, chimpanzees extended their arms above their heads to hold onto branches like a person going down a ladder as their greater weight pulled them downward rump-first.
“Our findings are among the first to identify the significance of ‘downclimbing’ in the evolution of apes and early humans, which are more genetically related to each other than to monkeys,” Fannin said.
“Existing research has observed…
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