EARLY humans may not have walked on their knuckles before they stood up on two feet. Instead, our ancestors walked upright in the trees and then set foot on the ground, according to a study comparing the wrist bones of our closest relatives.
Sceptics of this "trees to two feet" idea argue that the ancestor of all African apes, including gorillas, chimps and humans, must have been a knuckle-walker, because both gorillas and chimps knuckle-walk. They also have specialisations such as ridges and concavities on the wrist bones that keep the palm of the hand from collapsing onto the ground when bearing weight. It seems reasonable to think that bipedal walking in humans evolved from this intermediate stage, they argue.
Not so, says Tracy Kivell, a palaeoanthropologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. She and her colleague Daniel Schmitt of ...
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