Not our mom – Neanderthal DNA suggests no relation to humans

Not our mom – Neanderthal DNA suggests no relation to humans – includes related article

Robert Kunzig

A small stretch of DNA from a Neanderthal bone was described this past year, and it doesn’t look like ours. The bone was the right humerus, or upper-arm bone, of the Neander Valley skeleton itself, discovered near Dusseldorf in 1856; the DNA was from the “control region” of mitochondrial DNA. The control region codes for nothing, and so natural selection ignores it; and sex does too, because unlike the DNA that makes us visibly who we are, the stuff in the cell nucleus, mitochondrial DNA is passed intact from mother — and only from mother — to child. In theory, the control region comes to each one of us out of the deep past, like a taste for chicken soup, via an endless bucket brigade of mothers, altered only by random mutations. If some of us had a Neanderthal in that maternal line, her imprint ought to be discernible. Svante Paabo of the University of Munich and his colleagues looked at the DNA from their single Neanderthal, and they looked at DNA from more than, 1,600 modern Europeans, Africans, Asians, native Americans and Australians, and Oceanians. They saw no evidence of a relation.

The work was widely hailed as a technical triumph — reassuring in a year when earlier reports of far more ancient DNA from insects in amber seemed to be crumbling (see story on page 47). Few labs besides Paabos’s, it seems clear, would have been able to extract the Neanderthal DNA from liquefied bone samples that contained only some 50 copies of the target molecule. A graduate student named Matthias Krings did the hard work — amplifying the scare DNA by means of the polymerase chain reaction, cloning it, and finally determining its sequence. “It was Krings who put in the 100-hour weeks,” says Ralf Schmitz of the Rheinisches Amt fur Bodendenkmalpflege, an agency responsible for archeology in the Rhineland. “When he saw there might be something in there, he just kept working until he was sure.”

But it was Schmitz, a young archeologist, who made the project happen in the first place. In 1991 the Rheinisches Landesmuseum in Bonn authorized him to organize new studies of its prize fossil. Schmitz got in touch with Paabo, who had extracted DNA from a 30,000-year-old horse buried in permafrost. At first Paabo was discouraging: the chances of getting DNA out of a Neanderthal that was anywhere from 30,000 to 100,000 years old and that had not been frozen, he said, were very slim — too slim to convince the custodians of the fossil. “It’s as if you’re cutting a piece out of the Mona Lisa to study the paint,” says Schmitz. “You have to have good arguments for doing that.”

By 1996, though, gene-extraction techniques had improved, Paabo was willing, and Schmitz got permission. In June of that year, he and Heike Krainitzki, a professional bone preparator, entered the steel vault where the bones are stored in a steel box in a steel cabinet — the Landesmuseum keeps only the skullcap with the famous browridges on display. “The nervous tension was enormous,” Schmitz recalls. “We were both very tense. Krainitzki didn’t want anyone else to be there. A German TV network had wanted to broadcast it live, but she wouldn’t do it.” The two of them wore protective clothing and surgeons’ masks to avoid contaminating the bone. With a goldsmith’s saw Krainitzki cut a half-inch thick, eighth-of-an-ounce, half-moon slice from the right humerus — the bone that X-rays and other tests had shown was best preserved. She and Schmitz then immediately carried the slice to Munich. There Krings drilled tiny samples from the cortex; the hard calcium carbonate in that outer layer offers DNA more protection against the outside world than it gets in the marrow.

Five months later Schmitz was back in Munich again. By then, after all those hundred-hour weeks, Krings had extracted a bit of DNA that he thought was Neanderthal. He was now repeating the whole experiment with a separate hundredth-of-an-ounce bit of bone drilled from that half-moon slice. If he got the same DNA sequence again, he would be virtually certain he was not looking at a modern human contaminant. The results, Schmitz remembers, came in one November evening at 10:14 P.M. “It felt as if we had climbed Everest,” he says. Later there would be another occasion for celebration: the results were confirmed by an independent laboratory, that of Mark Stoneking at Penn State, which got the same sequence from another bit of the Neanderthal bone.

Careful controls like that seem to have convinced the researchers’ peers, after the paper was published last July, that Krings and his colleagues did indeed have the first bit of Neanderthal DNA and the oldest bit of DNA ever extracted from a human being. What sort of human the Neanderthal was, however, remains subject to debate. There are two main schools of thought. One holds that Neanderthals are our ancestors, or rather the ancestors primarily of modern Europeans; in this view modern humans evolved from archaic ones such as Neanderthals in different parts of the world simultaneously, all the while exchanging enough genes to remain part of the same species. The other view is that Neanderthals were a separate species that were replaced, after little or no fraternization, by modern humans, who began migrating out of Africa around 100,000 years ago.

The Neanderthal DNA does not resolve the issue — but it suggests Neanderthals were indeed a separate species, and thus it favors the out-of-Africa hypothesis. Krings’s 379-nucleotide sequence differed at 27 positions, on average, from the modern human sequences, and it was no closer to Europeans than to any other moderns. Among themselves the modern sequences differed by an average of only eight places. Picture a crowd of modern humans huddled around a campfire, with nobody more than eight yards from the center; then the Neanderthal is 27 yards away, well outside the circle, in the shadows at the edge of the woods. By Paabo’s and Krings’s calculations, Homo sapiens and Homo neanderthalensis must have evolved separately for more than half a million years to have become so different.

Of course, the researchers have only looked at one bit of DNA from one Neanderthal. Only when they or others have compared it with DNA from a second Neanderthal will the Munich result be fully convincing. It is fitting, though, that the first Neanderthal — and even from one of the bones that stayed the shovels of the miners in 1856, after they had already unwittingly tossed the skullcap and other bones out of Little Feldhofer Cave, down into the valley of the Dussel River. There is no Neander River, you see; the valley got its name in the late seventeenth century from a preacher and poet who often went there, a man named Joachim Neumann. In English his name would be Newman, but in the fashion of his day Neumann translated it into Greek, and it became Neander. A century and a half later, by a remarkable coincidence, the New Man Valley yielded a truly new man — a separate species of human, it now seems. It is wonderful, really, that after another century and a half, the Neanderthal Man himself should once again be in the news.

SON OF CHEDDAR MAN

The village of Cheddar, in the picturesque hills of Somerset in southwest England, is noted, of course, for its cheese; of the caves at Cheddar Gorge; and for Adrian Targett, a history teacher at Kings of Wessex Community School. Targett found out last March that he is related to 9,000-year-old Cheddar Man, the most complete ancient skeleton ever found in Britain.

A local TV company working on a documentary about the historic area had contacted Bryan Sykes, a geneticist at Oxford, to see if he could extract and DNA from Cheddar Man. Sykes was interested in comparing the genes of modern Britons to the preagricultural hunter-gatherers of Cheddar Man’s time, so the project suited him perfectly. The producers then asked Targett to find local students willing to be part of the sample modern population. To show his students that the method of DNA sampling, a cheek swab, was painless, Targett himself participated.

After analyzing a 400-nucleotide sequence of mitochondrial DNA in the samples (from the same “control region” that was extracted from the Neanderthal Man), Sykes found that Targett and Cheddar Man differed at only one spot. The two must have shared a maternal ancestor, perhaps someone as close as Cheddar Man’s mother. “He’s clearly quite closely related,” says Sykes. Targett, however, knew nothing of this until the results were revealed to him and his class on camera. “It was a bit surprising,” he says. “The presenter said `We have a result,” and he turned toward me and said `and it’s you.’ At least I didn’t say anything that had to be deleted out of the recording.”

Finding a match for Cheddar Man wasn’t totally unexpected, says Sykes, who estimates that about 1 percent of the British population carries a similar bit of DNA. What’s surprising, but apparently coincidental, is that Targett lives just half a mile from the cave where Cheddar Man was discovered in 1903. “I applied for 50 teaching jobs all over the country, and I happened to get the job here,” Targett says. He’s never seen the actual skeleton of his ancestor at the British Museum in London (and has no plans to reclaim it), “but I’ve become closely acquainted with the replicas,” he says, “because I keep being asked to be photographed next to them.”

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