After six years of analysis, fossil hunters in Africa have confirmed the discovery of the oldest fossilized remains of modern humans yet found -- portions of skulls belonging to people who lived 160,000 years ago. Paleontologists say the discovery adds detail to a crucial period in human evolution, and confirms the hypothesis that modern humans evolved in Africa. NPR's Christopher Joyce reports.
A team led by University of California, Berkeley paleontologist Tim White found the fossils in desert sands near the Ethiopian village of Herto.
"These are the oldest fossils that we can confidently place in our own species, Homo sapiens," says White.
The bones were uncovered in 1997, but it took six years to clean the pieces, glue them together and analyze their features. Because the fossils were in volcanic sediment, they could be reliably dated based on radioisotopes in the soil. White's team puts their age at 160,000 years. That beats the previous record for a human fossil by tens of thousands of years.
Two of the skulls from Herto belonged to adult males, and one to a child of six or seven. Each of the adult skulls was remarkably big.
"We compared this with skulls of 6,000 modern humans, and still after that comparison not one was as big and robust as the Herto male," says White. "These were very, very large robust people."
And yet they were also like modern-day humans in almost every feature. The face is flat with prominent cheekbones, but without the protruding brow ridge of pre-human ancestors or Neanderthals. And the braincase is rounded, like a soccer ball, rather than the football shape of earlier human ancestors.
There are other fossils of early humans almost as old. But they're only fragments, and the dating is unreliable -- a common problem in paleontology. But these skulls are almost complete, says Harvard paleontologist Daniel Lieberman, and that provides what paleontologists crave: certainty.
"What's really exciting about these fossils is that they are the best early modern humans we have ever found and the best dated -- this is just like nailing the coffin shut," says Lieberman. "We've got a good date now."
The fossils also confirm what genetic research has recently proposed: that modern humans evolved in Africa. There's little question that pre-human ancestors first appeared in Africa. Or that about 2 million years ago, they left Africa to populate parts of Asia, the Middle East and Europe. But some say primitive humans evolved into modern humans in many places around the world. Others, such as paleontologist Chris Stringer from the Museum of Natural History in London, say modern humans clearly evolved in in Africa.
"What this discovery in Ethiopia shows is that the shared features of modern humans -- our high-rounded brain case, small brow ridges -- originated in Africa," says Stringer.
Those first real humans, he says, most likely left Africa in a second wave that eventually replaced the remnants of the first, pre-human diaspora.
According to Berkeley's Tim White, the evidence also lays to rest any notion that Neanderthals were direct human ancestors. Rather, he says, they were a branch of pre-human evolution that remained isolated in Europe.
The study appears in the current issue of the journal Nature.
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