Walking in the trees.

New Scientist goes out on a limb with a new study that hints that humans may have learned to walk up in the branches before marching on the ground:

Kivell thinks the wrist bones of chimpanzees may instead have adapted to stabilise the wrist while standing on one tree branch and holding onto another, with knees and elbows bent…. “When you’re walking on ice, you bend your elbows and knees to make yourself more stable,” says Kivell. “You do the same thing when you’re walking on a branch.”

Indeed, modern chimps and bonobos do exactly that. The posture may put more bending strain on the wrist, leading to the kinds of adaptations visible today, Kivell says. She and her colleagues hope to test this idea in the future.

Advocates of the knuckle-walking theory are not convinced.