Nicholas WADE,
Trackinz the Movements of Early Humans.

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, has long been a corridor for armies 
and peoples traveling between Europe and Asia.

Dr- Underhill has 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, 8000 to 3000 
years ago. 

Anatolians with another lineage may be descendants of the Bronze Age Hattic 
culture, he said. 

Curiously the Seljuk Turks, who wrested Anatolia from the Byzantine Empire 
in the 11th 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 40000 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 40000 to 50000 years ago and 
populated first Asia and then Europe. 

But some geneticists think there may have been an earlier exodus of people 
who traveled by boat along the southern 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 term for the random change that takes place 
between generations as some genetic variants become more common and 
others get rarer or disappear.