A leg bone fragment of a Neanderthal man who died 38,000 years ago has unlocked the genetic secrets of the closest evolutionary relatives to modern humans, scientists said Wednesday.

Two teams of researchers have reconstructed a segment of Neanderthal DNA through the bone fragment and presented their initial analysis in this week's issues of Nature and Science.

The researchers said the Neanderthal data will shed light on what DNA changes helped produce modern humanity by revealing which changes appeared relatively late in human evolution, after the ancestors of Neanderthals and of humans split apart.

The genetic material has let researchers identify more than a million building blocks of Neanderthal DNA so far, and it should be enough to derive most of the creature's 3.3 billion blocks within the next two years, said Svante Paabo, one of the team's researchers at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

99.95 per cent like us

The Neanderthal sequences are 99.95 per cent identical to human DNA sequences, the scientists said. This compares to about a 98 per cent similarity between humans and chimpanzees, who are believed to have split from a common ancestor six million to seven million years ago.

"We're at the dawn of Neanderthal genomics," said gene expert Edward Rubin of the Lawrence Berkeley National Laboratory in Berkeley, Calif.

Such research will "serve as a DNA time machine that will tell us about the biology and aspects of Neanderthals that we could never get" otherwise, Rubin said.

DNA analysis indicated that the bone fragment came from a male. Further study could reveal details such as the colour of hair, eyes and skin of Neanderthals, as well as whether they were capable of modern speech function.

The bone fragment was taken from a sample that lay in a Croatian cave for 38,000 years and was largely ignored by researchers until recently.

"It's rather small and uninteresting and was thrown into a big box of uninformative bones" at a museum in Zagreb, Paabo said.

The bone's DNA was not extensively contaminated because it wasn't handled much, which was good news to researchers, he added.

No evidence of interbreeding

The two teams basically agree, within their margins of error, that the evolutionary lineages of Neanderthals and modern humans split somewhere around 500,000 years ago.

Neanderthals and anatomically modern humans coexisted in Europe for thousands of years, until Neanderthals died out 28,000 years ago. Scientists have been debating whether the two groups interbred and whether modern humans carry some genetic remnants of Neanderthals.

One U.S. scientist recently suggested modern humans might have acquired a variant of a specific brain gene through interbreeding with Neanderthals.

Rubin said his analysis, like some previous work, found no evidence of such intermixing, although it will take more DNA to rule it out.

Paabo's analysis didn't directly address whether modern humans have DNA from Neanderthals, but it did raise speculation that DNA from anatomically modern humans might have found its way into Neanderthals.

With files from the Associated Press