Further controversy on human origins
New research supports the theory that the ancestors of modern humans came from many different regions of the world, not just a single area -- but critics remain far from convinced.
The study, published in the current issue of Science by University of Michigan anthropologist Milford H. Wolpoff and colleagues, is the second study in a week to fuel the debate on the origin of the human species.
Australian researchers set off a storm last week when they announced that their analysis of mitochondrial DNA from 'Mungo Man' also supported the so-called 'regional continuity theory'. Their study is due to be published this month in the Proceedings of the National Academy of Sciences.
The study presented in this week's Science comes to the same conclusion following a comparison of early modern and archaic fossil skulls from around the world.
"Ancient humans shared genes and behaviours across wide regions of the world, and were not rendered extinct by one 'lucky group' that later evolved into us," says Wolpoff. "The fossils clearly show that more than one ancient group survived and thrived."
The researchers analysed the similarities and differences between fossil skulls from Australia and Central Europe, and peripheral regions far from Africa, where according to the dominant "Out of Africa" theory -- also known as the "Eve" or "Replacement" theory -- modern humans evolved.
"Basically we wanted to see if this comparison could disprove the theory of multiple ancestry for the early European and Australian moderns," said Wolpoff.
The researchers said they found that the most recent European and Australian skulls shared characteristics with the ancient African and Near Eastern population and with the older fossils from within their own regions. They also found there were many more similarities than could be explained by chance alone -- a finding which amounted to "a smoking gun" for the regional continuity theory.
The findings are the latest evidence in the continuing scientific controversy about the origin of modern humans (Homo sapiens). Most 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. If this theory was true it would mean 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 Australian National University anthropologist Dr Alan Thorne, maintain that there is little evidence that a small group originating in a single geographic region replaced the entire population of early humans.
"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."
Palaeoanthropologist Associate Professor Peter Brown of the University of New England disputes the findings.
"I'm amazed that Science has published this article. If it had been submitted to me by a third year student I would have failed them," he told ABC Science Online.
Professor Brown said that Wolpoff and colleagues had chosen an Australian fossil that was unrepresentative of the skulls of that time.
"It's pathologically different. It has a skull as thick as a bike helmet," he said. "They've just chosen a fossil that suits their theory".
He said that the authors had also ignored literature that was contrary to their theory.
Dr Alan Thorne, however, insists that the evidence is on his and Wolpoff's side.
"What we've found is mitochondrial DNA in an Australian fossil that is much more primitive than anything that's been found in Africa," he said. "And there is no archaeological or physical evidence to support the idea that Aboriginal Australians originated from Africa."