Credit: Credit: artwork and composite byJohn Gurche, photograph by Brian Richmond
Early human upright walking. A 6 million-yea- old thighbone, or femur (center), represents an upright walker of one of the earliest human ancestors (Orrorin), and resembles 2-3 million year old thighbones of australopiths (left, bottom). Thighbones of Homo (right) mark a transition toward a more modern gait about 2 million years ago.