First footing, as scientists find an old acquaintance
Until now it was believed the characteristic human foot and ability to walk upright on two legs emerged around 1.9 million years ago.
But scientists have made a discovery of human-like footprints dating back almost 3.7 million years in rock sediment in Laetoli, Tanzania.
The prints display a gait more like that of modern humans than the awkward posture adopted by chimpanzees, orang-utans and gorillas when they walk upright.
Eleven individual prints were found in good condition. In contrast, previous finds have generally been of single prints, making it difficult to distinguish between genuine and artificial features.
The footprints are thought to belong to Australopithecus afarensis, a primitive early human that may be a direct ancestor of everyone living today.
Lead researcher Professor Robin Crompton, from the University of Liverpool, said: "It was previously thought that Australopithecus afarensis walked in a crouched posture and on the side of the foot, pushing off the ground with the middle part of the foot, as today's great apes do.
"We found, however, that the Laetoli prints represented a type of bipedal walking that was fully upright and driven by the front of the foot, particularly the big toe, much like humans today, and quite different to chimpanzees and other apes."