When human ancestors evolved to walk upright, they may have done so in trees, suggests new research published [December 14] in the journal Science Advances.
The findings contrast with a prevailing theory about human bipedalism—walking on two feet—known as the savanna hypothesis. This theory posits that human ancestors began walking upright when forests retreated and the landscape transformed into more open, savanna-like areas. As a result, hominins began spending less time in trees and more time on the ground, traveling and foraging for food, per the hypothesis. The ability to walk on two feet would have been helpful for seeing over tall grass, as well as for carrying objects, scientists suggested.
However, the new research proposes human ancestors instead may have begun walking upright to move around tree branches in search of food.
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Scientists reached this conclusion after studying wild chimpanzees—which are humans’ closest living relatives—in the Issa Valley of western Tanzania. The chimpanzees’ environment is what’s known as a savanna-mosaic, which features both open landscapes with few trees and densely forested areas with lots of trees. Scientists were keen to study these chimpanzees, because this environment closely resembles that of early human ancestors.
