The Caveman in Us

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 skin, and the total size of the Neanderthal population.

The first goal of the project will be to sequence three billion units of Neanderthal DNA, corresponding to the full length of the Neanderthal genome. This will require decoding 20 times as much DNA, because so much of the DNA in the Neanderthal bones belongs to bacteria. Genomes usually must be decoded several times over to get a complete and accurate sequence, but the first three billion bases of Neanderthal should ‘‘hit all the essential differences’’, Dr Michael Egholm, vice-president of 454 Life Sciences, said.

One of the most important results that researchers are hoping for is to discover, from a three-way comparison of 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 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 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 like 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, 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 and to local diseases. Evidence from the human genome suggests 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.

If Paabo and 454 Life Sciences should succeed in reconstructing the entire Neanderthal genome, it might in theory be possible to bring the species back from extinction by inserting the Neanderthal genome into a human egg and having volunteers bear Neanderthal infants. This might be the best possible way of finding out what each Neanderthal gene does, but there would be daunting ethical problems in bringing a Neanderthal child into the world again.

Ronald M Green, an ethicist at Darmouth College, said there could be arguments in the future for resurrecting the Neanderthals. ‘‘If we learn this is a species that was wrongly pushed off the stage of history, there is something of a moral argument for bringing it back,’’ he said. ‘‘But the status quo is not without merit. Curiosity alone could not justify what could be a disaster for both species.’’

(NICHOLAS WADE)