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Neanderthal DNA will help to unlock the secrets of humanity

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« on: August 10, 2007, 01:38:13 am »

Neanderthal DNA will help to unlock the secrets of humanity
By Mark Henderson, Science Editor


NEANDERTHAL Man has begun to give up his genetic secrets almost 30,000 years after he last walked the Earth, providing critical insights into the genes that make human beings what they are today.

DNA extracted from a Neanderthal bone has been analysed in detail for the first time and the genetic code of humanity’s closest cousin will be mapped completely within two years, scientists announced yesterday.

The development will allow scientists to compare the human genome with that of our nearest living and extinct relatives — the chimpanzee and the Neanderthal — to tease out the differences between the three. These variations will in turn reveal the genes that make us human.

A gene found only in Homo sapiens, but not in chimps or Neanderthals, must have evolved recently and is therefore solely part of Modern Man’s genetic heritage. Genes that we share with Neanderthals, but not with chimps, will also have played a part in human evolution, but at an earlier stage, before we diverged from our extinct cousins.

“For all the differences we know of between humans and chimps, we will be able to ask: is that a recent change in the human lineage after the separation from Neanderthals, or is it an older one?” said Svante Pääbo, of the Max Planck Institute in Leipzig, Germany, who led the research.

“We can look for evidence of positive selection in language genes after the separation from Neanderthals, and ask which are the biological reasons that made us different from our ancestors.”

Henry Gee, senior editor of Nature, which published Dr Pääbo’s research, said: “We can get a good idea of which changes are unique to humans and which are common to wider human lineages.”

Small amounts of Neanderthal DNA have been sequenced before but Dr Pääbo’s group used new technology to sequence a million Neanderthal DNA base pairs — about 0.03 per cent of the total — taken from a 38,000-year-old fossil found in Croatia, according to reports in Nature.

A second team, led by Edward Rubin, of the US Lawrence Berkeley National Laboratory, in California, has used a different method to sequence 69,000 base pairs from the same fossil. Its results are published in the journal Science.

The same specimen was used for both studies as it is the only one available that has not been seriously contaminated by human and bacterial DNA.

Dr Rubin said that the work was tantamount to resurrecting Neanderthal Man for science. “We are never going to be able to bring it back to life, but we are going to be able to compare its genome to the human genome,” he said.

With so little of the Neanderthal genome covered so far, neither team has yet hit on a gene that is significantly different from those found in humans. The work has, however, confirmed smaller genetic studies which suggested that humans and Neanderthals never interbred on a significant scale.

“Our data cannot absolutely exclude it, but we see no evidence that pages are being ripped off one genome and being pasted into the other,” Dr Rubin said.

Dr Pääbo’s research dates the evolutionary split between humans and Neanderthals to between 465,000 and 569,000 years ago, with a best guess of 516,000 years ago. Dr Rubin’s estimates are 120,000 years ago to 670,000 years ago, with a best guess of 370,000 years ago.

Professor Chris Stringer, head of human origins at the Natural History Museum, London, said that the achievement promised to transform understanding of Neanderthal biology and human evolution. It would be particularly interesting to look for the microcephalin gene, a contributor to the form of the brain, in Neanderthals as it had been suggested that this was introduced to Homo sapiens quite recently, perhaps through interbreeding with Neanderthals.

GENETIC DIVIDE

The species became extinct soon after, probably as a result of climate change and competition with Homo sapiens

http://www.timesonline.co.uk/tol/news/uk/article638368.ece
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