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Friday, April 3, 2009

Multiple out-of-Africa migrations seen for early humans

Multiple out-of-Africa migrations seen for early humans

March 23, 2009
World Science staff

Fossil evidence suggests that early, anatomically "modern" humans may have split into many isolated populations before leaving Africa in a series of migrations, scientists report.

Scientists generally believe humans evolved in Africa and from there spread out to other regions, starting over 60,000 years ago.

In new research, Gerhard Weber of the University of Vienna and colleagues used geometric patterns of fossilized skulls found in various parts of Africa to compare the diversity among early representatives of the genus Homo, the evolutionary group to which humans belong.

The researchers concluded that, rather than a single out-of-Africa dispersal, their evidence shows early modern humans in Africa were divided into different populations by the Pleistocene, the era from about two million to 11,000 years ago.

Skulls from early modern humans showed the greatest variation in shape over the last 1.8 million years, indicating that early modern humans had split into multiple, temporarily isolated populations, the researchers explained.

After that breakup there seems to have followed a complex migration pattern in which different populations left the continent left at different times, they added. They report that the skull shapes of early modern humans most closely resembled those found in later humans outside of Africa, providing a link between some isolated African populations with later migration.

Understanding the diversity of anatomically modern humans in Africa before the migrations is crucial to any analysis of modern human origins, the researchers wrote in a paper detailing their findings. "The African continent deserves more attention in the modern human origins debate," they added in the paper, to appear in this week's early online edition of the research journal Proceedings of the National Academy of Sciences.


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