A rchive Date
[ 13-06-2003 ]
Category
[ Science ]
sub-Categoy
[ Archaeology ]
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[http://www.chron.com/cs/CDA/ssistory.mpl/world/1948530
Discovery of skulls puts new face on man's origin
Scientists marvel at 160,000-year-old fossils
By JOHN NOBLE WILFORD
New York Times
June 11, 2003, 10:55PM
In the 160,000-year-old fossilized skulls of two adults and a child found in Ethiopia, scientists think they see for the first time the faces of the immediate ancestors of modern humans.
Except for a few archaic characteristics, the skulls are readily recognizable. They are longer than their Neanderthal contemporaries from Eurasia or earlier ancestors. Their midfaces are broad, but the nasal bones are tall and narrow. The brow ridges are less prominent than the glowering visages looking down from earlier branches of the family tree. The cranial vaults are higher and within modern dimensions.
The discovery of the oldest near-modern human remains, announced Wednesday, is considered a major step in establishing the time and place for the emergence of anatomically modern Homo sapiens, probably about 150,000 years ago in Africa, as genetic studies have suggested.
"We can now see what our direct ancestors looked like," said Dr. Tim D. White, a paleoanthropologist from the University of California at Berkeley, who is a leader of the international team that excavated and analyzed the skulls.
That had been impossible until now because of the frustrating gap in fossil evidence between 100,000 and 300,000 years ago, when the transition from prehumans to modern humans is thought to have occurred.
Dr. Christopher Stringer of the Natural History Museum in London, who did not participate in the research, hailed the findings as "some of the most significant discoveries in early Homo sapiens so far."
Another independent observer, Dr. Richard G. Klein of Stanford University, said, "These are basically modern people, remarkably modern in appearance."
The discovery team and other scientists said in interviews that the research appeared to confirm the idea that modern humans originated in Africa and then spread into Asia and Europe. In that case, they said, the enigmatic Neanderthals, which became extinct in Europe 30,000 years ago, could not have been direct forebears of today's humans.
In a report in today's issue of the journal Nature, released online Wednesday morning, White and his collaborators concluded that the Ethiopian skulls "represent the probable immediate ancestors of anatomically modern humans" and that "their anatomy and antiquity constitute strong evidence of modern-human emergence in Africa."
The "out of Africa" hypothesis, forcefully advocated by Stringer among others, had gained wide support in the two decades since molecular research on the genetic diversity among human populations pointed to a common ancestor in Africa, which inevitably became known as the African Eve. The research was based on evolutionary changes in mitochondrial DNA, which is passed from mother to daughter. Other studies of the male Y chromosome reached similar conclusions.
But scientists had been unable to pin down the time of origin or find supporting fossil evidence. The earliest fossils of modern Homo sapiens, from Ethiopia, South Africa and Israel, are not much more than 100,000 years old.
If correct, White's group emphasized, the new research ruled out the alternative multiregional hypothesis, held by a minority of scientists. They proposed that modern humans evolved in different parts of Africa, Asia and Europe at roughly the same time from ancient local populations. The Homo erectus species, which had migrated out of Africa much earlier, were thought to have evolved into Asian humans and European humans, possibly through intermediate stages, including Neanderthals.
Dr. Milford Wolpoff of the University of Michigan, who is a leading proponent of the multiregional theory, questioned whether the skulls had any bearing on the Neanderthals' place in human evolution.
"All the specimens show is that there was a trend of evolution in Africa toward modernity, just as there was in China and Europe," Wolpoff said.
But White's group said the fossil skulls showed that Homo sapiens with almost entirely human characteristics had already evolved in Africa before Neanderthals evolved into their classic form. Soon afterward, fully modern Homo sapiens entered Europe, presumably from Africa by way of the Middle East, and the Neanderthals went into decline.
"We can conclusively say that Neanderthals had nothing to do with modern humans," said Dr. Berhane Asfaw, a co-leader of the discovery team from the Rift Valley Research in Addis Ababa, the Ethiopian capital.
In a background news release to the journal articles, the discoverers said that even if descendants of the transitional people from Ethiopia "interbred with surviving Neanderthal populations, the latter appear to have contributed very little to the modern human gene pool."
The team concluded, "In this sense, we are all African."
The skull fossils were found in 1997 in an arid valley bordering the Middle Awash River near the village of Herto, 140 miles northeast of Addis Ababa. The fossils were buried between layers of volcanic ash, from which project geologists determined their age to be about 160,000 years. The fossils were so badly fragmented, however, that it took years of cleaning, reassembling and analyzing before the discoverers felt they could report their findings.
"The key point is that we now have good fossil evidence of people like us evolving in Africa when the only people in Europe were Neanderthals," said Klein of Stanford. "The Herto humans are anything but Neanderthals."]
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