Mystery surrounds Australasian DNA link


Scientists have found a genetic link between the indigenous peoples of Australia and South America.

Two separate studies have succeeded in discovering the unexpected connection which links the native inhabitants of the Amazon with the indigenous peoples of Australia and Melanesia.

It is generally accepted that the first people to reach the Americas got there by crossing a land bridge between Siberia and Alaska, but the precise date at which this first happened and what countries they originated from has always remained a topic of debate.

One theory suggests that the first people to arrive in North America did so around 23,000 years ago and that they later split in to two branches with some heading to South America.

Other theories however predict multiple waves arriving in the Americas at different times.

The connection is ancient, all agree, and attributable to Eurasian migrants to the Americas who had some Australasian ancestry, the scientists said.

But one group said the evidence is clear that two different populations came from Siberia to settle the Americas 15,000 or more years ago. The other scientific team says there was only one founding population from which all indigenous Americans, except for the Inuit, descended and the Australasian DNA came later, and not through a full-scale migration. For instance, genes could have flowed through a kind of chain of intermarriage and mixing between groups living in the Aleutian Islands and down the Pacific Coast.

Both papers were based on comparisons of patterns in the genomes of many living individuals from different genetic groups and geographic regions, and of ancient skeletons.

David Reich of Harvard, the senior author of a paper published Tuesday in the journal Nature, said the DNA pattern was “surprising and unexpected, and we weren’t really looking for it.”

“The simplest possible model never predicted an affinity between Amazonians today and Australasians,” said Prof David Reich from Harvard Medical School.

“This suggests that there is an ancestral population that crossed into the Americas that is different from the population that gave rise to the great majority of Americans. And that was a great surprise.”

According to Prof Reich the most likely explanation is that a separate migration from Australasia occurred around 15,000 years ago with those people eventually being pushed towards the south by the existing Native American groups who had populated North America before that time.