WORLD SCIENCE

"Long before it's in the papers"
December 20, 2005

Posted May 13, 2005
Courtesy Science
and World Science Staff

The first modern humans to leave East Africa and populate Asia seem to have left as a single group and followed a coastal route, researchers have found. 

This contrasts with a traditional view among scientists that the humans traveled through the Middle East.

The findings are among the conclusion of studies published in today’s issue of the research journal Science. One of these two finds that the dispersal was a single, rapid event that could have led to the subsequent peopling of Europe and Asia.

Many scientists believe that modern humans populated Europe and Asia after dispersing out of Africa sometime between 45,000 and 80,000 years ago, depending on the estimates. The details of this journey, however, have been unclear.

Much of what we know about human migrations comes from studying a set of genes known as mitochondrial DNA. This genetic material is inherited maternally. 

The amount of variation among different groups’ mitochondrial DNA generally reflects the amount of time since the groups branched off from each other genetically. 

Kumarasamy Thangaraj and colleagues at the Centre for Cellular
and Molecular Biology in Hyderabad, India, used this approach to study indigenous tribal populations on the Andaman and Nicobar Islands, which lie between India and Myanmar.

They identified two relatively old populations of Andaman Islanders that probably survived in isolation there since the out-of-Africa migration. Their genes are considered useful for study because they are relatively unmixed with those of other populations.

In contrast, the Nicobarese populations appear to be closely related to other populations in Southeast Asia. This suggests their ancestors arrived much more recently from the east, the researchers said.

The mitochondrial DNA of the aboriginal Orang Asli of Malaysia also supports the idea that humans leaving Africa dispersed along a southern coastal route through India and into southeast Asia and what is now Australia, according to a second study. 

The Orang Asli likely branched off from other Asian lineages around 60,000 years ago, soon after their ancestors left Africa.

Vincent Macaulay of the University of Glasgow in Glasgow, Scotland, and his international research team propose that there was an early offshoot, leading to the settlement of the Near East and Europe, but that the main dispersal from India to Australia was quick, taking only a few thousand years. 

A related commentary in the journal notes that populations such as the Andamanese and the Orang Asli are dwindling, so time is short for gathering data about them.

Note: this story has been corrected since its original posting. The original article said most scientists believe modern humans left Africa around 45,000 years ago. In fact, the estimates vary considerably (see above).

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