Don Johanson describes finding the knee joint in Hadar, Ethiopia, that first indicated a bipedal hominid had lived 3 million years ago, in this video from NOVA: In Search of Human Origins. Johanson's subsequent expedition led to the discovery of Lucy, a 40-percent-complete skeleton of a new species of hominid, now known as Australopithecus afarensis. The final piece of the puzzle was a skull from the same site, which clearly demonstrated that Lucy and her kind were small-brained, although they walked upright.