for National Geographic News
Three fossil skulls recovered from the windswept scrabble of Ethiopia's dry and barren Afar rift valley lend archaeological credence to the theory that modern humans evolved in Africa before spreading around the world.
The fossils include two adult males and one child and are estimated to be 160,000 years old. They were found among stone tools and butchered hippopotamus bones. Cut marks on the skulls suggest an early form of mortuary practice.
Prior to the discovery of these fossils, evidence for the out-of-Africa theory of evolution for modern humans was largely based on the analysis of genetic variation in people alive today. Archaeological evidence from 100,000 to 300,000 years ago was scarce.
As a result, another theory that modern humans evolved simultaneously in various parts of the world at roughly the same time from ancient local populations, such as the Neandertals in Europe, maintained plausible traction.
Timothy White, a paleoanthropologist at the University of California at Berkeley, said that the fossils he and his colleagues found in Ethiopia fill this gap in the archaeological record and support the argument that Neandertal was an evolutionary side branch unrelated to modern humans.
"The genetic data predicted we would find fossils that showed none of the characters we see in Neanderthal but rather would show characters on their way to becoming us, and indeed we have tested that hypothesis by finding these new fossils," he said.
The international team of scientists recovered the fossils outside the pastoral Afar village of Herto in 1997. Since the discovery, White and his colleague Berhane Asfaw have methodically dated, pieced together, and analyzed the fossils. They published two papers on the find in the June 12 issue of Nature.
"We are all very pleased we can contribute new information on a period that was previously very poorly known," said White, who serves as the team's American spokesperson.
Owing to the mix of primitive and modern features exhibited by the fossil skulls, White and colleagues assign them to a new subspecies of Homo sapiens they named Homo sapiens idaltu. Idaltu means elder in the Afar language.
Chris Stringer, a paleontologist at the Natural History Museum in London, said that "in terms of completeness and dating these are perhaps the most important early human fossils found."
Previous fossils purportedly from this epoch have been fragmentary and were not well dated. The fossils from Ethiopia, however, were found sandwiched between two layers of ash from regularly erupting volcanoes and are very well preserved.
"These are complete enough to show they are modern humans and they are really well dated," said Stringer, who wrote an accompanying perspective in Nature on the find.
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