The Japan Times
December 1, 2001
By Robin McKie
London

Mankind learned to walk while living in trees, scientists believe

It is the key, defining ability of our species, the one critical evolutionary feature that sets us apart from other creatures. Yet the reason for humanity developing a prowess to walk on two legs has baffled paleontologists for decades.

Despite investigating myriad theories, no researcher has satisfactorily explained why prehistoric ape-men and women got up and remained on their hind feet.

But now a group of scientists has proposed a controversial theory which maintains our upright ability is far more ancient than supposed. They also claim we picked up our two-footed prowess while living in trees. The skills of soccer player David Beckham and dancer Michael Flatley can be traced to this ancient arboreal event.

"Trees were an ideal nursery for the learning of human walking," says Robin Compton of Liverpool University. "They enable an animal to balance itself. They can reach out in any direction, above and below themselves, and find branches. Orangutans do just this sort of thing."

And having got our bipedal act right, we were then perfectly placed, when the climate changed 2 million years later, and forests thinned, to walk out on the savanna with our hands free to make tools and carry food to caves.

This startling evolutionary idea has been put forward by scientists led by Martin Pickford, of the College de France, and Brigitte Senut, of the National Museum of Natural History in Paris. As they claim in "Secrets of the Dead: The first human?" on Channel 4 television in Britain, their discovery of ape-men's bones in Kenya last year provides evidence we could walk on two feet at least 6 million years ago, although most scientists believe our bipedal expertise did not appear for another 2 million years.

The new claim is based on the use of advanced techniques to date soil in which the bones of the ape-man Orrorin tugensis were found. Apart from revealing their antiquity, their studies show the fossils belonged to upright creatures and must therefore be direct ancestors of humans today, the group state.

One femur contains a groove that held muscles linking the bone to the animal's thigh and is typical of a creature that walked on two feet. In addition, 3-D X-ray scans reveal thickening of Orrorin femurs in areas that showed it had a bipedal gait. "Orrorin is something apart from the apes," says Pickford. "Walking, running, standing were major parts of its repertoire."

But, if it is correct, that interpretation raises headaches — for Africa was thickly forested 6 million years ago. There were no plains on which ape-men could have strutted their upright stuff.

So they must have learned to walk in the trees, using branches to help them adopt an upright manner. As the team point out, Orrorin had curved hand and arm bones, typical of a creature that used to hang on to vines and creepers as it moved about.

Many scientists disagree, however. They believe our two-footed gait appeared more recently, possibly to allow us to carry objects or reduce the area of our bodies exposed to harsh African sunlight.

"On its own, the discovery of any 6-million-year-old ape-man is important, but I don't think evidence for its upright gait has been established," Professor Leslie Aiello, of University College London, says. "The scientific community has not had a chance to study these bones yet. They could belong to the ancestor of an ape, not a human."

Professor Chris Stringer of the Natural History Museum London was also doubtful: "Surely it would have been more difficult to pass through dense tree foliage in an upright position."

U.S. paleontologist Don Johanson, of Arizona University, was more supportive. "We could have had tree nests and lived in trees for millions of years," he says.

Regardless of the date of our move to bipedalism, no one disputes its impact. "As a pure problem in architectural reconstruction, upright posture is far-reaching and fundamental, an enlarged brain superficial and secondary," Harvard paleontologist Stephen Jay Gould says. Our silky football skills, not our intellects, define us, in short.

CHIPPY THE CHIMPANZEE may be one of our closest ancestors, but where did he learn to walk? AFP PHOTO