Footprints reveal how early humans first walked

By AAP and AG staff 21 July 2011
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The discovery of ancient intact footprints suggest early humans began walking upright earlier than thought.

HUMAN FEET WERE WALKING in far more ancient times than previously thought, research has shown.

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 new discovery of human-like footprints dating back almost 3.7 million years.

The prints, preserved in rock sediment in Laetoli, Tanzania, display a gait more like that of modern humans than the awkward upright walking posture adopted by chimpanzees, orangutans and gorillas.

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 have been left by Australopithecus afarensis, a primitive early human that may be a direct ancestor of everyone living today.

Fully upright

Scientists compared their analysis of the prints with data from footprint studies of modern humans and apes. Computer simulations were also used to predict what kind of footprints would have been formed by different gaits.

“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,” says lead researcher Professor Robin Crompton, from the University of Liverpool. “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 bipedal walking of chimpanzees and other apes.

“Quite remarkably, we found that some healthy humans produce footprints that are more like those of other apes than the Laetoli prints. The foot function represented by the prints is, therefore, most likely to be similar to patterns seen in modern humans. This is important because the development of the features of human foot function helped our ancestors to expand further out of Africa,” he says.

The research, published in the Royal Society journal Interface, suggests the ability to walk in a modern human way evolved almost four million years ago in a species thought to have spent at least some of the time in trees.

However, other aspects of the Australopithecus afarensis body design were quite unlike those of modern humans, says Robin. “The characteristic long-legged, short body form of the modern human allows us to walk and run great distances, even when carrying heavy loads.”

Australopithecus afarensis had the reverse physical build, short legs and a long body, which makes it probable that it could only walk or run effectively over short distances. We now need to determine when our ancestors first became able to walk or run over the very long distances that enabled humans to colonise the world,” he says.

Ground-dwelling development

Co-author Dr Bill Sellers, from the University of Manchester, says that the “shape of the human foot is probably one of the most obvious differences between us and our nearest living relatives, the great apes. The difference in foot function is thought to be linked to the fact that humans spend all of their time on the ground, but there has been a lot of debate as to when in the fossil record these changes occurred. Our work shows that there is considerably more functional overlap than previously expected.”

“The Laetoli footprint trail is a snapshot of how early human ancestors used their feet 3.7 million years ago. By using a new technique for averaging footprints, foot pressure information from modern great apes, and computer simulation of walking in the proposed Laetoli printmaker, we can see that the evidence points to surprisingly modern foot function very early on in the human lineage.”