Human Shoulders and Elbows First Evolved as Brakes for Climbing Apes
Published:01 Apr.2024 Source:Dartmouth College
Dartmouth researchers report in the journal Royal Society Open Science that apes and early humans likely evolved free-moving shoulders and flexible elbows to slow their descent from trees as gravity pulled on their heavier bodies. When early humans left forests for the grassy savanna, the researchers say, their versatile appendages were essential for gathering food and deploying tools for hunting and defense.
The researchers used sports-analysis and statistical software to compare videos and still-frames they took of chimpanzees and small monkeys called mangabeys climbing in the wild. 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.
Luke Fannin, first author of the study and a graduate student in Dartmouth's Ecology, Evolution, Environment and Society program, said the 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. Existing research has observed chimps ascending and navigating trees -- usually in experimental setups -- but the researchers’ extensive video from the wild allowed them to examine how the animals' bodies adapted to climbing down, Fannin said.