Knuckle-walking

Knuckle-walking is a form of quadrupedal walking in which the forelimbs hold the fingers in a partially flexed posture that allows body weight to press down on the ground through the knuckles.

Gorillas and chimpanzees use this style of locomotion as do anteaters and platypuses.

Anthropologists once thought that the common ancestor of chimpanzees and humans engaged in knuckle-walking, and humans evolved upright walking from knuckle-walking: a view thought to be supported by reanalysis of overlooked features on hominid fossils.

Since then, scientists discovered Ardipithecus ramidus, a human-like hominid descended from the common ancestor of chimpanzees and humans. Ar. ramidus engaged in upright walking, but not knuckle-walking. This leads scientists to conclude that chimpanzees evolved knuckle-walking after they split from humans 6 million years ago, and humans evolved upright walking without knuckle-walking.