ANN ARBOR --- The ancestors of modern humans came from many different regions of the world, not just a single area, according to a University of Michigan study published in the current (Jan. 12) issue of Science. The study, by U-M anthropologist Milford H. Wolpoff and colleagues, is one of just a few to base its controversial conclusion about the origin of the human species on a comparison of actual human fossils---early modern and archaic fossil skulls from around the world.
"Ancient humans shared genes and behaviors across wide regions of the world, and were not rendered extinct by one 'lucky group' that later evolved into us," says Wolpoff, a professor of anthropology at the U-M and first author of the study. "The fossils clearly show that more than one ancient group survived and thrived."
For the study, Wolpoff and colleagues John Hawks of the University of Utah, David W. Frayer of the University of Kansas, and Keith Hunley of the U-M, examined some of the first early modern human fossil crania from Australia and Central Europe, peripheral regions far from Africa, where modern humans evolved, according to the Eve theory. They compared these Europeans and Australians (between 20,000 and 30,000 years old) with two even older groups who might be their ancestors---archaic fossil crania from the same locations, and even earlier fossils from Africa and the Near East, who would have to be the only ancestors for both of them according to the Eve theory. If the Europeans and Australians had multiple ancestry, including ancestors among their local archaic predecessors, the Eve theory would have to be wrong. "Basically we wanted to see if this comparison could disprove the theory of multiple ancestry for the early European and Australian moderns," notes Wolpoff.
Wolpoff and colleagues selected fossils from Eastern Europe and Australia for the focal point of the comparison because they thought that populations distant from the center of the ancient human population might retain easily identifiable resemblances to ancient peoples, if there were any. They compared a number of different features of the fossil skulls from the Mladec cave in the Czech Republic and a skull from the Willandra Lakes region of Southeastern Australia to the other fossil skulls that could be ancestors. In each case, they analyzed in how many respects the Mladec and Australian skulls were like the other skulls and in how many respects they were different.
They found that the Mladec and Australian skulls shared characteristics distinctive to the more ancient African and Near Eastern population. But at the same time, the fossils also had distinctive resemblances to more ancient fossils within their regions, many more than could be explained by chance alone. "These features amount to a smoking gun for continuity within these regions, " says Hawks.
The findings are the latest evidence in the continuing scientific controversy about the origin of modern Homo sapiens. Many scientists believe that all living humans can trace their ancestry exclusively to a small group of ancient humans, probably Africans, living around 100,000 years ago. This explanation, known as the Eve hypothesis or replacement theory, means that all other early human groups, whose fossils date from this time back to almost two million years ago, must have become extinct, possibly wiped out in a prehistoric genetic holocaust.
Other scientists, including Wolpoff and colleagues Hawks, Frayer, and Hunley, maintain that there is little evidence that a small group originating in a single geographic region replaced the entire population of early humans. The genetic evidence has always been unclear, Wolpoff and colleagues note, because different genes support different theories: mitochondrial genes support replacement theory while nuclear genes support the development of an older, worldwide species of human ancestors.
"In asking the question a different way, and directly addressing the fossils, this study provides compelling evidence that replacement is the wrong explanation," says Wolpoff. "Instead, the findings support the theory of multi-regional evolution. Modern humans are the present manifestation of an older worldwide species with populations connected by gene flow and the exchange of ideas. Modern human groups are very much more similar than different because of comparable adaptations to ideas and technologies that spread across the inhabited world and because of the dispersals of successful genes promoted by selection."
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