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Svante Paabo, prehistoric sleuth

Pioneer of ancient DNA discovered our Neanderthal link and a mystery species

by Robin Mckie

The Observer

Leipzig’s Max Planck Institute of Evolutionary Anthropology is a striking edifice.

Set among the drab housing blocks of former East Germany, the building, erected in 2003 and made largely of glass, curves gently like a banana around the edge of a suburban crescent.

There is a pond in its huge forecourt with turtles and ducks. Television screens in its ground-floor cafeteria relay live images of orangutans and chimps from the city’s zoo. There is a grand piano in one corner, and above it a climbing wall rises to the main atrium’s ceiling several floors overhead. For good measure, there is a sauna on the roof.

It is not clear whether staffers relax by climbing the institute’s walls to the sound of a Liszt concerto before taking a rooftop sauna. If they do, they have Svante Paabo to thank.

“The climbing wall and sauna were my ideas,” he said. “When they put together plans for the institute and asked me work here, I insisted they have these. I suppose they fit in with my Swedish identity.”

Paabo is the institute’s head of evolutionary genetics and an idiosyncratic researcher, a man obsessed with the avoidance of contamination and the need to keep his laboratories and researchers scrupulously clean.

In doing so, Paabo has transformed the study of human origins.

Among his achievements, he has sequenced an entire Neanderthal genome, revealing a link between these extinct people and many modern humans. He has also uncovered the existence of a previously unknown human species, called the Denisovans, from DNA extracted from a finger bone found in a cave in Siberia.

“When I started this field 25 years ago, I thought we might be able to extract DNA from bones of people born a few thousand years ago and learn something about the ancient Egyptians or about the people who brought agriculture into Europe,” said Paabo. “It was beyond my wildest dreams to think we could resurrect genomes that are hundreds of thousands of years old. To have done that, well, it’s really cool.”

It is also incredibly difficult. DNA, the stuff from which our genes are made, decays the moment an organism dies. The long coils break down into fragments, and the longer the passage of time, the shorter the fragments become.

Trying to put these pieces together is a stunningly complex task that has been likened, by writer Elizabeth Kolbert, to trying “to reassemble a Manhattan telephone book from pages that have been put through a shredder, mixed with yesterday’s trash, and left to rot in a landfill.”

Yet Paabo has succeeded in this remarkable task, a story he recalls with striking frankness in “Neanderthal Man: In Search of Lost Genomes,” to be published by Basic Books later this month.

Nobel winner’s secret son

Near the beginning, the 58-year-old geneticist says he was inspired to a life scientific by his biochemist father. It is only later that he reveals how odd was this paternal inspiration. “I grew up as the secret extramarital son of Sune Bergstrom, who won the 1982 Nobel Prize for discovering prostaglandins,” he said. Bergstrom’s “official” family knew nothing of the existence of Paabo and his mother, the Estonian chemist Karin Paabo, with whom the Nobel laureate had had an affair. “He would only visit us on Saturdays,” said Paabo. “It was pretty weird, with hindsight.” Bergstrom died in 2005. “It was only then my half-brother learned about me. Fortunately, he adjusted and we get on alright.”

Paabo studied medicine and later biochemistry at Uppsala University, where he began working with researchers who studied DNA to understand its relationship to disease. “They were interested in its role in living people, but I wanted to know what it could tell us about ancient people.” Paabo consulted textbooks but could find no references to DNA being extracted from dead tissue. No one had really thought about it.

So, in the summer of 1981, he launched his career in ancient forensics, although he kept his work secret to avoid incurring the displeasure of his professor for indulging in “frivolous” activities.

“I bought a piece of liver and stuck it in a laboratory oven, heated to 50 C, for several days,” he said. Paabo broke open the liver, by now hard, black and dry, and managed to extract DNA from it. The DNA had been broken down into small sections only a few hundred nucleotide pairs long, compared with strips measuring thousands of nucleotide pairs from fresh DNA.

Nevertheless, there was sufficient DNA to back his belief that if genetic material was extracted from old bones, it could be used to create an entirely new way to probe the past: not through studying skulls, spears or hand axes, but by analyzing our predecessors’ shredded biological leftovers.

Paabo then tried to extract DNA from several Egyptian mummies and managed to isolate a short segment from the 2,400-year-old mummy of an infant boy. He wrote up the results for Nature in 1985, which the journal made its cover story, an astonishing achievement for a fledgling researcher.

A job at Munich University followed, and in the early 1990s Paabo turned to a more ambitious project: Neanderthal DNA.

The first remains of these ancient folk had been dug up in the 19th century in the Neander Valley in Germany, and are now reckoned to belong a subspecies of humans that became extinct 30,000 years ago.

Most paleontologists believe Neanderthals were overrun by genetically distinct modern humans when we emerged from our African homeland and spread around the world. Paabo decided to investigate.

It took several years of diplomacy before Paabo was given an arm bone from the original Neander Valley skeleton, from which he extracted a 3.5-gram sample of whitish bone.

Paabo tried to isolate DNA from its mitochondria, the cells’ power packs. Mitochondrial DNA is much shorter and more plentiful and so would be a better initial target, he reckoned. Paabo isolated several DNA sequences that were clearly different from those of any human beings living today. The story made headlines around the world.

Then came the call from the Max Planck Society and an offer to join leading biologists, evolution experts and paleontologists to establish a world-class anthropology center in Leipzig.

Neanderthals live in us

Fired by his early achievements, Paabo announced that his group would sequence a full Neanderthal genome.

His results provided a shock for both researchers and the public.

When he compared his newly created Neanderthal genome with those of modern humans, he found a small but significant overlap in many of them.

About 2 percent of Neanderthal genes could be found in people of non-African origin. Most scientists, including Paabo, now account for this result by arguing that modern humans encountered and mated with Neanderthals in the Middle East when they emerged from Africa. Their offspring carried some Neanderthal genes, and as modern humans swept through Asia and Europe they carried these genes with them.

Paabo’s Neanderthal work is a towering scientific achievement. Yet the geneticist managed to top it in 2010 when his team announced that they had sequenced DNA from a tiny fragment of finger bone found in the Denisova cave in Siberia, and had shown it belonged not to Neanderthals, as they had expected, but to an entirely new human species, the Denisovans.

More closely related to Neanderthals than modern humans, this ancient human “was the first new form of extinct humans to be described from DNA sequence data alone, in the total absence of any skeletal remains,” Paabo said.

This last point is intriguing. We have a fully sequenced Denisovan genome, thanks to Paabo, but no idea what a Denisovan might have looked like. (A bit “Neanderthalish” is his best guess.)

“Obviously there is a limit to how far back we can go in time with this approach,” he said. “DNA fragmentation is a real issue. Nevertheless, I think one day that we will be able to sequence DNA that is 500,000 years old — and possibly a million years. And who knows what that will throw up?”