Saturday, February 21, 2009

NEANDERTHAL GENOME

Scientists report that they have reconstructed the genome of Neanderthals, a human species that was driven to extinction some 30,000 years ago.

The Neanderthal genome, when fully analyzed, is expected to shed light on many critical aspects of human evolution. It will help document two important sets of genetic changes: those that occurred between 5.7 million years ago, when the human line split from the line leading to chimpanzees, and 300,000 years ago, when Neanderthals and the ancestors of modern humans parted ways; and second, the changes in the human line after it diverged from Neanderthals.

An early inference that can be drawn from the new findings, which were announced Thursday in Leipzig, Germany, is that there is no significant trace of Neanderthal genes in modern humans. This confounds the speculation that modern humans could have interbred with Neanderthals, thus benefiting from the genes that adapted the Neanderthals to the cold climate that prevailed in Europe in last ice age, which ended 10,000 years ago. Researchers have not ascertained if human genes entered the Neanderthal population.

Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig led a team that had to overcome daunting technical obstacles to produce the draft of the Neanderthal genome. He was assisted by the company 454 Life Sciences, which invented a new DNA decoding machine that works by analyzing millions of very small fragments of DNA in parallel. DNA from Neanderthal bones is fragmented in just this way.

Dr. Pääbo began his project more than 10 years ago, when he succeeded in extracting the first verifiable piece of Neanderthal DNA. Most Neanderthal bones have no recoverable DNA and those that do are heavily contaminated with modern human DNA from the many scientists and curators who handled them. Distinguishing human and Neanderthal DNA is hard because they are so similar.

Archaeologists have long debated whether Neanderthals could speak, and they have eagerly awaited Dr. Pääbo’s analysis of the Neanderthal FOXP2, a gene essential for language. Modern humans have two changes in FOXP2 that are not found in chimpanzees, and that presumably evolved to make speech possible. Dr. Pääbo said Neanderthals had the same two changes in their version of the FOXP2 gene. But many other genes are involved in language, so it is too early to say whether Neanderthals could speak.

Dr. Richard Klein, a paleoanthropologist at Stanford University, said Dr. Pääbo’s project was “incredibly exciting” and could eventually shed light on the behavioral differences between Neanderthals and modern humans

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