Thursday, May 12, 2005


When humans first left Africa, which way did they go?

For many years specialists assumed these early migrants headed through what is now Egypt, across the Sinai and into the Middle East.

But new evidence suggests they may have taken a more southerly route, along the coasts of the Arabian peninsula into India, Indonesia and Australia.

Two reports in today’s issue of the journal Science raise the possibility of the coastal route. The studies are based on comparisons of mitochondrial DNA in various native populations.

DNA is the coded set of instructions in cells that enables reproduction. The form found in the mitochondria, the energy-producing portion of cells, is inherited from the mother. By studying differences in mitochondrial DNA, scientists can estimate how long ago one group of people diverged from another group.

In one paper, a team led by Vincent Macaulay of the University of Glasgow, Scotland, proposes a single dispersal from Africa along a coastal route to India and Australia. An offshoot led later to the settlement of the Middle East and Europe.

Researchers studied the mitochondrial DNA of the Orang Asli, an aboriginal population in Malaysia. These people branched off from other Asian lineages about 60,000 years ago, soon after their ancestors left Africa, the team said.

By comparing that DNA and that of other groups in India, Australia and other locations, researchers concluded there was a relatively rapid coastal dispersal that began about 65,000 years ago around the Indian Ocean and into Australia.

A second paper reports the study of indigenous tribal populations on the Andaman and Nicobar Islands, between India and Burma.

These researchers, led by Kumarasamy Thangaraj of the Center for Cellular and Molecular Biology in Hyderabad, India, found two relatively old populations of Andaman Island residents that probably survived in genetic isolation since the out-of-Africa migration.

But this team concluded that the Nicobarese populations were more closely related to other populations in Southeast Asia, suggesting that their ancestors arrived much more recently from the east.

Peter Forster and Shuichi Matsumura of the University of Cambridge, England, hoped the papers would inspire further research in the area.

The Cambridge scientists, who were not part of either research team, noted in a commentary that the age estimates for early populations can add support to the idea of a population spread that occurred first along the coasts.

If the original Africans had moved into the Middle East and north, then why was Europe settled thousands of years after Australia, they asked in a commentary. In Europe, Neanderthals were replaced by modern humans 40,000 to 30,000 years ago, while southern Australia had been settled as early as 46,000 years ago.

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