Humans and chimpanzees split from a common ancestor 6 million years ago. But how quickly did we swap the benefits of climbing for those of walking? A new line of study suggests that we made the jump early in our development.
Anthropologist Jeremy DeSilva found that chimps flex their ankles by as much as 45 degrees when climbing, while humans can manage only 15 or 20 degrees. Next, he compared great-ape ankles with the ankles of our oldest humanlike ancestors. To his surprise, DeSilva found that those ancestors already had ankles that were more human than apelike. The takeaway? Given that climbing confers big advantages — escape from predators, access to fruit — the benefits of walking upright (and keeping our hands free for defense, attack, and other work) must have been big enough from the get-go for it to become a dominant trait.
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