A 40,000-YEAR-OLD skeleton found in China has raised questions about the "out of Africa" hypothesis on how early modern humans populated the planet.
The fossil bones are the oldest from an adult "modern" human to be found in eastern Asia.
They contain features that call into question the widely held view that all humans alive today are descended from a small group of sub-Saharan Africans who made their way out of the continent about 60,000 years ago. Gradually they colonised other parts of the planet, replacing older human species such as the Neanderthals, which became extinct. The older humans had themselves originated in Africa but moved out more than 1 million years earlier.
A rival theory suggests modern humans evolved into their present form in a number of locations around the world, not just Africa.
The new discovery came after local workers stumbled across the bones in Tianyuan Cave, in Zhoukoudian, near Beijing. Experts reported on Monday in the journal Proceedings of the National Academy of Sciences that they had dated the skeleton to between 38,500 and 42,000 years ago. It was the first properly dated adult modern human from eastern Asia known to be more than 30,000 years old.
However, certain features of the individual were puzzling, said the scientists, led by Dr Hong Shang from Washington University in St Louis, Missouri.
As well as having "modern" human traits, the skeleton had physical characteristics normally seen in Neanderthals and other ancient humans such as Homo erectus. These included the difference in size between the front and back teeth, unusually thick and sturdy leg bones, and enlargement of a wrist bone called the hamulus.
The scientists said it was likely there was "at least substantial gene flow" from modern humans who had settled in regions to the south and west of Tianyuan Cave at an earlier date.
But they added: "At the same time,the presence of several archaic features
implies that a simple spread of modern human morphology eastward from Africa is unlikely."
