Researchers in Germany said Thursday that they planned to collaborate with an American company in an attempt to reconstruct the genome of Neanderthals, the archaic human species that occupied Europe from 300,000 years ago until 30,000 years ago until being displaced by modern humans.
Long a forlorn hope, the sequencing, or decoding, of Neanderthal DNA suddenly seems possible because of a combination of analytic work on ancient DNA by Svante Paabo, of the Max Planck Institute for Evolutionary Anthropology in Leipzig, and a new method of DNA sequencing developed by a Connecticut company, 454 Life Sciences.
The initial genome to be decoded comes from Neanderthal bones, 45,000 years old, which were found in Croatia, though bones from other sites may be analyzed later. Because the genome must be kept in constant repair and starts to break up immediately after the death of the cell, the DNA surviving in Neanderthal bones exists in tiny fragments 100 or so units in length. As it happens, this is just the length that works best with the 454 machine, which is also able to decode vast amounts of DNA at low cost.
Recovery of the Neanderthal genome, in whole or in part, would be invaluable for reconstructing many events in human prehistory and evolution. It would help address such questions as whether Neanderthals and humans interbred, whether the archaic humans had an articulate form of language, how the Neanderthal brain was constructed, if they had light or dark skins, and how big the Neanderthal population was.
One of the most important results that researchers are hoping for is to discover, from a three-way comparison between chimp, human and Neanderthal DNA, which genes have made humans human. The chimp and human genomes differ at just 1 percent of the sites on their DNA. At this 1 percent, Neanderthals resemble humans at 96 percent of the sites, to judge from the preliminary work, and chimps at 4 percent. Analysis of these DNA sites, at which humans differ from the two other species, will help understand the evolution of specifically human traits “and perhaps even aspects of cognitive function,” Paabo said.
The degree of resemblance between humans and Neanderthals is fiercely debated by archaeologists and even issues such as whether Neanderthals had language have not been resolved.
Paabo believes that genetic analysis is the best hope of doing so. He has paid particular attention to a gene known as FOXP2, which from its mutated forms in people seems to be involved in several advanced aspects of language.
A longstanding dispute among archaeologists is whether the modern humans who first entered Europe 45,000 years ago, ultimately from Africa, interbred with the Neanderthals or forced them into extinction. Interbreeding could have been genetically advantageous to the incoming humans, says Bruce Lahn, a geneticist at the University of Chicago, because the Neanderthals were well adapted to the cold European climate — the last ice age had another 35,000 years to run — and to local diseases.
Evidence from the human genome suggests some interbreeding with an archaic species, Lahn said, which could have been Neanderthals or other early humans.
So far no specific evidence of human-Neanderthal interbreeding has been found, Egholm said. But it may require analysis of almost the full Neanderthal genome to rule out all possibility of genetic interchange.
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