It was a continent thought to have been uninhabited by humans until around 15,000 years ago when the 'First Americans' came across a tiny strip of land over the Bering Strait.

A new genetic study, however, is threatening to transform theories about who the original Native Americans were after finding certain tribes in the Amazon are related to Aborigines in Australia.

The findings suggest America may have actually experienced multiple waves of migration thousands of years ago, rather than just one that spread down through the continent from the north.

Geneticists have found that Native American tribes living in the Amazon are most closely related to Aborigines from Australia, Papau New Guinea and the Andaman Islands, as shown in the image above, where warm colours show the greatest level of genetic affinity. White circles show populations with no genetic link

Researchers found people belonging to the Suruí, Karitiana and Xavante peoples in the Amazon are more closely related to indigenous populations in Australasia than any other modern group.

Australian Aborigines, together with indigenous populations in New Guinea and the Andaman Islands, are thought to be descended from one of the earliest groups of modern humans to migrate out of Africa around 60,000 years ago.

ABORIGINES HAVE WORLD'S OLDEST ORAL HISTORY Traditional stories passed down through generations by Australian Aborigines may be among the oldest accurate oral histories in the world. Researchers believe these stories could constitute some of the oldest accurate oral histories in the world, passing through some 300 generations. They are using them to map how the continent may have looked around 10,000 years ago. Oral folklore tells how the Great Barrier Reef once formed part of the coastline of north east Queensland, while Port Phillip Bay in Victoria was once a rich place for hunting kangaroo and opossum. Researchers have found other stories from all over the continent that mirror how the landscape dramatically changed towards the end of the last ice age. They say at this time sea levels rose as a result of the melting of the huge ice caps that covered much of the northern hemisphere around 10,500 years ago. Advertisement

They are thought to have been a sea faring people who were able to hop between the islands that extend from Asia to Australia.

The new findings suggest their descendants may have ranged far further and could have crossed the vast ocean expanse between Australia and south America.

However, the researchers say they could have also travelled across ice sheets to the north.

Professor David Reich, a geneticist at Harvard Medical School who led the study, said: 'It's incredibly surprising.

'There's a strong working model in archaeology and genetics, of which I have been a proponent, that most Native Americans today extend from a single pulse of expansion south of the ice sheets—and that's wrong.

'We missed something very important in the original data.

'About 2 per cent of the ancestry of Amazonians today comes from this Australasian lineage that's not present in the same way elsewhere in the Americas.'

The researchers, whose work is published in the journal Nature, analysed the DNA from 21 Native American populations in Central and South America.

They also collected and analysed DNA from nine populations in Brazil before comparing it to the genomes of people from 200 non-American populations.

They found the Tupí-speaking Suruí people who first came into contact with the modern world in 1969, the Karitiana tribe, who live in western Amazon, and the Ge-speaking Xavante people in Eastern Brazil, all had genetic links to indigenous Australians.

Native Brazilian people like the Xavante (above) may owe much of their origins to the ancestors of Aborigines in Australasia. Two other tribes, the Suruí and the Karitiana, were also found to have a similar genetic ancestry

However, the scientists could not find any other traces in other Native American groups in South, Central or North America.

The researchers say the genetic signals do not match any population known to have contributed to Native American ancestry and the geographic pattern cannot be explained by post-colonial European, African or Polynesian mixture with Native Americans.

Instead they believe the genetic link may be as old as the first human populations to colonise the continent.

It raises the prospect that the Aborigine populations may even have been living in the area before Native Americans arrived.

Australian Aborigines, like those pictured above, are thought to be descended from one of the earliest groups of modern humans to migrate out of Africa. It seems as well as colonising Australasia, they also extended as far away as South America, leaving a their mark in the DNA of native people living in the Amazon today

The researchers say their findings echo suggestions that skeletons of early Native Americans found in Brazil have skulls that have Australasian features.

The researchers have now named the mystery ancestors as Population Y after the after the Tupí word for ancestor, 'Ypykuéra'.

Dr Pontus Skoglund a geneticist at Harvard Medical School who was part of the team, said: 'We don't know the order, the time separation or the geographical patterns.

'We've done a lot of sampling in East Asia and nobody looks like this. It's an unknown group that doesn't exist anymore.