KNM-ER 1470 is know held at the Smithsonian Institutuion in Washington D.C.

Credit: Smithsonian Institution/Wikipedia

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SYDNEY: The ancestors of modern humans resembled apes much more recently than thought, according to a new and unprecedented reconstruction of a fossil skull.

According to U.S. scientists behind the research, humans may have developed their large brains and flat facial profiles as many as 300,000 years later than previously thought.

In 1972 renowned paleoanthropologist Richard Leakey and his team unearthed a fragmented fossil skull in Kenya and reconstructed it by hand. The skull - later dated at 1.9 million years old - belonged to a member of the species Homo rudolfensis, the earliest member of the genus Homo, to which we ourselves belong.

Leakey argued that the skull belonged to one of our first 'human-looking' ancestors, and experts have though it represents the transition to the larger brain, relatively flat facial profile, less pronounced jaw and smaller teeth that define the genus Homo.

However, a new much more detailed reconstruction of how that skull would have looked in life now challenges that idea.

Palaeoanthropologist and craniofacial biologist Timothy Bromage of the New York University College of Dentistry, in New York City, developed a computational method for analysing how the bones of the face grow in living animals and people. He then applied this method to the study of fossil human faces and found that our earliest human ancestors had faces that grew in a fashion more indicative of apes rather than humans.

Bromage also found that the reconstruction of Leakey's famous skull, called KNM-ER 1470, didn't agree with the pattern of facial development his analysis predicted.

"I discovered that the plan of the face, which is common to all mammals, was way off in the reconstruction of this skull," Bromage told Cosmos Online. "Also it was odd that the reconstructed brain size of this skull was always [anomalous] with respect to all other early humans of that time period."

On repositioning the face of H.rudolfensis according to his model, Bromage found that it was protruding - more like an ape. His team also found that the brain was much smaller than previously estimated and more in line with early human contemporaries.

According to Bromage, who presented his findings this week at a meeting of the International Association for Dental Research in New Orleans, the premise that the skull belonged to the Homo genus may have prejudiced Leakey to reconstruct it with the supposed quintessential Homo traits of a flat face and a large brain.

"Leakey produced a biased reconstruction based on erroneous preconceived expectations of early human appearances that violated principles of craniofacial development," said Bromage. "Because he did not employ [biological] principles, he produced a reconstruction that could not have existed in real life."

It's not surprising that Leakey's original reconstruction was incomplete and distorted given the limited technology available at the time, commented Peter Brown, a palaeoanthropologist with the University of New England in Armidale, Australia. "Computer-based CT 3-D methods were not available before 1990, so mistakes were easily made," he said.

The interesting new reconstruction could have more wide-reaching implications, said biological anthropologist Colin Groves of the Australian National University in Canberra. It was on the basis of Leakey's original reconstruction that later anthropologists classified Homo rudolfensis as a separate species, he says.