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Human-like creature walked upright earlier than thought

10 September 2004

Studies of a thigh bone fossil have uncovered strong evidence that a human-like creature walked upright six million years ago rather than the widely accepted four million years ago.

Australopithecus afarensis illustration © The Natural History Museum, London 2005

Australopithecus afarensis illustration © The Natural History Museum, London 2005

Walking on two feet, bipedalism , is one of the characteristics that distinguishes apes from humans.

‘Dating the beginnings of bipedalism is very important in the human story,' said Chris Stringer, human evolution expert at the Natural History Museum. 'Because, for many experts, it would mark a clear divergence from the ancestral/ape pattern and show that the human lineage had really begun.'

‘Bipedalism probably does represent a fundamental first step in human evolution,’ Stringer said. ‘As Darwin recognised, walking on two legs frees up the arms and hands for tasks like carrying, tool making, and tool use. And much of what happened in human evolution later on stemmed from it.’

CT scans

CT (Computed tomography) scans were carried out on the fossil thigh bone and the density patterns of the bone were much closer to a modern human than to an ape.

Reported on the National Geographic website, Robert Eckhardt, who lead the research team at Pennsylvania State University, said ‘In present-day chimps and gorillas, the thicknesses in the upper and lower parts of that bone are approximately equal. In modern humans, the bone on top is thinner than on the bottom by a ratio of one to four or more.’  The ratio in the fossil was one to three, showing a bone formation more in line for an upright walker.

Eckhardt and the research team report their findings in the journal Science .