Human ancestors quickly found their feet
Hominids started walking on two legs six million years ago, shortly after diverging from chimpanzees, according to a study of the inner structure of a fossilised thighbone. The finding puts upright posture at the base of the human family tree. The evolution of upright posture is a key issue in anthropology. Together with large brain size, it marks the dividing line between humans and the great apes.