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Tracking the Movements of Early Humans
By Nicholas Wade

The New York Times 1-2 december 2002

COLD SPRING HARBOR, New York - Through the wizardry of modern genetics, it is possible to reconstruct the travels of the earliest humans as they moved out from their ancestral home in northeast Africa and spread around the globe. More details of these historic itineraries emerge each year, many at an annual conference of population geneticists and archaeologists at the Cold Spring Harbor Laboratory on Long Island in New York.
Geneticists can track these emigrations because of the train of errors that slowly accumulates in certain regions of the DNA. After a population splits, the people who go east will accumulate a different set of errors from those who venture West.

From the population splits implied by these error patterns, geneticists can reconstruct family trees of different lineages in the grand genealogy of humankind, and even assign rough dates to the branch points.
At this year's conference, which ended recently, Dr. Peter Underhill of Stanford University in California showed how scholars could begin to link the data in the genome's archive with historical events. Anatolia, the ancient name for Turkey, bas long been a corridor for armies and peoples traveling between Europe and Asia.
Dr. Underhill bas been analyzing the various Y chromosome lineages present in today's Turkish population. He has found one lineage whose ancestors may have carried the agricultural revolution from Anatolia to Europe during the Neolithic era, 8,000 to 3,000 years ago. Anatolians with another Meage may be descendants of the Bronze Age Hattic culture, he said. Curiously the Seljuk Turks, who wrested Anatolia from the Byzantine Empire in the llth century, left only a faint genetic signal of their presence, Dr. Underhill said. Though the conquerors imposed their culture over a wide region, an army of 40,000 made little genetic difference to a population that had reached 12 million by Roman times.
Most of the evidence suggests there was only one emigration of modern humans from Africa, a small group that left some 40,000 to 50,000 years ago an populated first Asia and then Europe. But some geneticists think there may have been an earlier exodus of people whd traveled by boat along the south ern'Asian coasts, eventually reaching Australia. The people of Australia and Papua New Guinea are dark skinned and somewhat different from most other Asians and Europeans.
To test the idea of a southern route, Dr. James F. Wilson of University College London compared the DNA of the dark skinned aboriginal tribes of southern India with that of New Guinea highlanders to see if the two might be part of the same exodus. The first gene he looked at suggested they were related, but further study showed otherwise.
"The distinctiveness of New Guineans could be from long-term drift, not a different route out of Africa," he said. Drift is the geneticist's terra for the random change that takes place between generations as some genetic variants become more common and others get rarer or disappear.


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