Scientists have uncovered a DNA signature supporting evidence from an ancient skull that American Indians were NOT the first the colonise the Americas.

Two sensational discoveries - an ancient skeleton and a rare DNA sequence - suggests an early European or Eurasian people crossed the Bering Strait to colonise the Americas thousands of years before the ancestors of American Indians arrived in North America.

Geneticists at Emory University in Atlanta, Georgia, have found a small minority of Amerindians share a rare genetic marker called Lineage X, with some Finns, Italians and Israelis - but there is no trace of Lineage X in Asian populations, including the presumed Siberian ancestors of most Amerindians.

The genetic discovery comes two years after the chance discovery of a human skeleton on a river bank near Kennewick, in Washington state in the north-western United States, with a long narrow skull of distinctively Caucasian, not Asian, features. Scientists were astonished when the skeleton of "Kennewick Man", initially thought to be an early European settler or fur trapper, yielded a radiocarbon age of between 9,200 and 9,600 years.

There have been no further DNA tests on Kennewick Man since its discovery in 1996. The skull, and other bones found associated with it, were appropriated by the U.S. Army Corps of Engineers, on behalf of the five Indian tribes from the region that have laid claim to the bones. The tribes claim Kennewick Man is their ancestor, dubbing him "The Ancient One".

In 1940, a mummified skeleton with similar Caucasian features was discovered in Spirit Cave in Nevada, in the American south-west. It was initially believed to be no more than 2,000 years old, but samples of hair and bone, and fibres from fragments of two textile mats wrapped around the mummy all yielded radiocarbon dates of about 9,400 years.

One of the mats featured a diamond-plaited pattern not used by any latter day Amerindian culture, and believed to have been created on a loom, suggesting the Spirit Cave culture 9,000 years ago had achieved a surprising degree of technological sophistication.

Now, geneticists at Emory University have found what may be the surviving genetic signature of the race to which Kennewick Man and the Spirit Cave people belonged - and the signature is not mongoloid (north Asian) but caucasoid (Caucasian-like).

The Emory University team, led by Michael Brown and Dr. Douglas Wallace, presented their findings to a meeting of the American Association of Physical Anthropologists in Salt Lake City, Utah, in March. They followed this with an article in the April 24 issue of the international research journal Science .

Dr. Brown and Dr. Wallace discovered the Lineage X marker in mitochondria, tiny structures that generate chemical energy in living cells.

With the help from Italian and German collaborators, they set out to establish the source population for the X variant, surveying mtDNAs (see below) from European, Asian and native American populations.

The U.S. researchers were expecting the X marker had penetrated Europe and Asia Minor from an Asian homeland - so they were astonished to find it was completely absent from modern Asian populations.

The challenge for anthropologists and geneticists is to explain how a caucasoid race carrying the X gene marker was able to colonise Asia, and cross the Bering Strait, without leaving its genetic calling card in Asia.

(* mtDNA: mitochondrial DNA escapes mixing between generations and is transmitted unchanged - unlike the DNA of the central genetic blueprint in the cell nucleus.)