Wednesday, 11 October, 2000, 15:13 GMT 16:13 UK

DNA clues to Neanderthals

Scientists have analysed the DNA of a third Neanderthal in an attempt to shed light on the genetic history of early humans.

The results suggest that, like modern humans, Neanderthals expanded from a relatively small number of individuals.

And there is no evidence to indicate that Neanderthals interbred with modern humans, something that has always been a bone of contention among experts.

The DNA was extracted from remains of a Neanderthal found in Vindija Cave, Croatia.

So far, only two other samples of DNA from Neanderthal bones have been analysed.

One came from fossils found in Feldhofer Cave, western Germany, the other from a Neanderthal child found in Mezmaiskaya Cave in the northern Caucasus.

Genetic diversity

The researchers compared regions of the Neanderthals' DNA with those of humans, chimps and gorillas.

"It allows us to start to say something about how much genetic variation there seems to have been among Neanderthals," said team leader Svante Paabo, Professor of Genetics and Evolutionary Biology at the Max Planck Institute for Evolutionary Anthropology, Liepzig, Germany.

"The major question is if they were more like humans in having very little genetic differences within the group, or much variation like chimpanzees and the other apes," he told BBC News Online.

"Although three individuals is still a very small number of individuals, the results suggest that they were more like us in having little variation rather than like the apes in having a lot.

"This may indicate that they had expanded from a smaller population as seems to be the case for modern humans, but that they represent an earlier expansion."

Interbreeding unlikely

The DNA sequence of Neanderthals could also solve another age-old mystery: whether interbreeding between Neanderthals and modern humans may have taken place.

Professor Paabo said: "Although we cannot exclude some degree of interbreeding, these results give no evidence that interbreeding took place.

"We want to study more Neanderthals as well as early modern humans to begin to reconstruct the genetic history of both groups at the time when they were contemporaneous with each other."

Neanderthals lived in Europe between about 130,000 and 30,000 years ago.

The bones used in the new study were dated to at least 42,000 years ago.

Last Neanderthals

Professor Chris Stringer, Head of Human Origins at the Natural History Museum, London, UK, said the three DNA studies gave scientists a glimpse of the genetic make-up of the Neanderthals.

"Neanderthals are different from modern humans - they are as different from Europeans as they are from Africans or Australians in this DNA," he said.

"Now with three of them you can start to build up a picture of their own variation and they are showing their own variation which is comparable to that of modern humans."

He said the genetic diversity of Neanderthals suggested that they declined in numbers at some point in history, perhaps because of climatic change. But unlike modern humans, they never recovered fully.

"The Neanderthals did recover too but they became extinct.

"They were never in huge numbers. Their recovery would have been a gradual recovery from some kind of bottleneck."