The Year in Science: Human Origins 1997

Not our Mom

By Robert Kunzig|Thursday, January 01, 1998
RELATED TAGS: NEANDERTHALS, GENETICS
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 Düsseldorf 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 Pääbo 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 Pääbo’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 scarce 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 für 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 Pääbo, who had extracted dna from a 30,000-year-old horse buried in permafrost. At first Pääbo 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, Pääbo 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 Pääbo’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 dna came from 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 Düssel 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.
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