Skulls confirm we're all out of Africa

Skeletal remains from the Anne and Bernard Spitzer Hall of Human Origins at the American Museum of Natural History are seen in New York,February 7, 2007. An analysis of thousands of skulls shows modern humans originated from a single point in Africa and finally lays to rest the idea of multiple origins, British scientists said on Wednesday.

LONDON (Reuters) - An analysis of thousands of skulls shows modern humans originated from a single point in Africa and finally lays to rest the idea of multiple origins, British scientists said on Wednesday.

Most researchers agree that mankind spread out of Africa starting about 50,000 years ago, quickly establishing Stone Age cultures throughout Europe, Asia and Australia.

But a minority have argued, using skull data, that divergent populations evolved independently in different areas.

The genetic evidence has always strongly supported the single origin theory, and now results from a study of more than 6,000 skulls held around the world in academic collections supports this case.

"We have combined our genetic data with new measurements of a large sample of skulls to show definitively that modern humans originated from a single area in Sub-Saharan Africa," said Andrea Manica of the University of Cambridge's Department of Zoology.

Manica and colleagues wrote in the journal Nature that variations in skull size and shape decreased the further a skull was away from Africa, just like variations in DNA.

The decrease reflects the fact that, while the original African population was stable and varied, only a small number of people embarked on each stage of the multi-step migration out of Africa. This effectively created a series of "bottlenecks", which reduced diversity.

The highest level of variation in skull types was seen in southeastern Africa, the generally accepted cradle of mankind.

The Cambridge work also suggests in-breeding with other early humans, such as Neanderthals, either did not happen or was insignificant. That is in contrast to recent suggestions that such hybrids may have been fairly common.

"We're not saying there was never a single mating between a homo sapiens and a Neanderthal. But I can say, very confidently, that whatever the product of that mating was, it didn't breed back into the population," Manica told Reuters.

Chris Stringer, a palaeoanthropologist at the Natural History Museum in London, said the new research was important for indicating that modern human diversity was derived entirely from Africa rather than coming from inter-mixing elsewhere.