'Eve theory' of human evolution discounted
SAN DIEGO (AP) Anthropologists analyzing ancient skulls from around the world say modern humans did not arise from one migration from Africa, but from small groups that journeyed to every continent and intermingled with archaic humans such as the Neanderthal.
In a study appearing Friday in the journal Science, the researchers said that distinctive features in ancient skulls, some dating back more than 200,000 years, suggest that modern humans descended independently from common ancestors that lived on nearly every continent and mingled with earlier human types.
"There was no single wave of modern humans out of Africa," said Milford H. Wolpoff, a University of Michigan anthropologist and coauthor of the study. Modern humans originated in Africa, but they migrated in small groups over thousands of years and journeyed to Asia, Europe and even as far as Australia, he said.
"It was not a single wave," Wolpoff said. "It was more like a leaky faucet. They moved out in dribbles."
This is contrary to the "Eve theory," which holds that modern humans evolved in Africa and moved into the rest of the world in one movement of perhaps 10,000 people. Once on the other continents, the theory holds, the moderns supplanted the more ancient humans, such as the Neanderthal.
But Wolpoff and his coauthors said that skulls dated 25,000 to 30,000 years from Europe and Australia share characteristics of 40,000- to 200,000-year-old archaic human skulls found in Europe, Indonesia and Africa.
The more recent skulls from Europe, for instance, showed clear evidence of a Neanderthal influence, along with features of the early modern humans that evolved in Africa. Early modern human skulls from Australia had similarities to more ancient skulls from Indonesia.
Wolpoff said this suggests modern humans dribbled out of Africa in small numbers and spread to distant lands, where they mingled with a more ancient human type that lived in those places.
Eventually, he said, the superior genes of modern humans dominated the species through natural selection, and the clearly identifiable archaic humans, such as the Neanderthal, disappeared.
"The Neanderthal disappeared as a result of interbreeding," Wolpoff said.
Traces of those archaic humans survive in the genes of modern humans, said John Hawks, a University of Utah anthropologist and coauthor of the study. And these genes produce distinctive markings on modern human skulls.