Their findings support the hypothesis that Asia was populated primarily through a single migration event from the south.

The researchers described their findings in the journal Science.

They found genetic similarities between populations throughout Asia and an increase in genetic diversity from northern to southern latitudes.

The team screened genetic samples from 73 Asian populations for more than 50,000 single-nucleotide polymorphisms (SNPs).

These are variations in pieces of the DNA code, which can be compared to find out how closely related two individuals are genetically.

Diversity explained

Edison Liu from the Genome Institute of Singapore was a leading member of the consortium.

He explained that the age of a population has a much bigger effect on genetic diversity than the population size.

"It seems likely from our data that they entered South East Asia first - making these populations older [and therefore more diverse]," he said.

"[It continued] later and probably more slowly to the north, with diversity being lost along the way in these 'younger' populations.

"So although the Chinese population is very large, it has less variation than the smaller number of individuals living in South East Asia, because the Chinese expansion occurred very recently, following the development of rice agriculture - within only the last 10,000 years."

Dr Liu said that it was "good news" that populations throughout Asia are genetically similar.

This knowledge will aid future genetic studies in the continent and help in the design of medicines to treat diseases that Asian populations might be at a higher risk of.

And the discovery of this common genetic heritage, he added, was a "reassuring social message", that "robbed racism of much biological support".

http://news.bbc.co.uk/1/hi/sci/tech/8406506.stm