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Hairs trace human history

 

Nuka Godfredsen
  An artist's impression shows how Inuk might have looked in life 4,000 years ago.


For the first time, scientists have deciphered the genetic code of an ancient human from a long-gone culture, using the DNA from just a few tufts of 4,000-year-old hair preserved in Greenland's permafrost.

Thanks to the rapid advance of gene-sequencing technology, researchers could tell the hair belonged to a brown-skinned man whose ancestors came to the New World from Siberia around 5,500 years ago, during a previously unknown migration. And that's not all.

The genetic evidence suggests that the man, nicknamed "Inuk," had the kind of eyes, teeth and even earwax associated with modern-day Asians and Native Americans ... and that he might have been going bald.

One of the research team's leaders said the technique used on Inuk's hair could be used on other ancient samples as well, almost literally fleshing out humanity's saga through the millennia. "I think it will be something we will see much more of in the coming five years," said Eske Willerslev, an evolutionary biologist at the University of Copenhagen.

After two years of study, the team published their findings in this week's issue of the journal Nature. The latest report follows up on earlier research published in the journal Science.

Scientists have been analyzing ancient DNA for years - and in fact, they've found out enough about the extinct Neanderthals' genetic code to conclude that at least some of them were redheads. But the study of Inuk (a name that comes from the Greenlandic word for "human") sets a new standard. The Neanderthal genome is only in rough-draft form, while Inuk's genome has been checked 20 times over (20x, in genomic parlance). That's about as good as it gets, even for modern-day genome sequencing.

"It is amazing how well-preserved this sample is, presumably due to its rather young age and the permafrost," Svante Pääbo, a geneticist who led the Neanderthal DNA study at the Max Planck Institute for Evolutionary Anthropology in Germany, told me via e-mail. "Eighty percent of the DNA is human, whereas at most 4 percent is from Neandertals in the bones we study. I am envious."

Edward Rubin, director of the U.S. Energy Department's Joint Genome Institute, was similarly impressed: "The coverage of the genome is such ... that they begin to get clues to what the flesh and blood of this creature was."

"It's really a time machine," said Rubin, who is based at Lawrence Berkeley National Laboratory in California.

'Freezing my butt off'
Willerslev is no stranger to Arctic artifacts and ancient DNA analysis: His past projects include studies of mammoth DNA preserved in Alaskan permafrost, as well as fossilized poop from Oregon, so it was natural for him to try to see whether such genetic techniques could be extended to ancient humans in the Arctic.

Willerslev went so far as to go on an Arctic expedition in 2006 to look for samples. "I was freezing my butt off up there," he recalled. But it turned out that the ideal specimens were already sitting in a Copenhagen museum.

The four hair samples were retrieved from Greenland's permafrost, along with four bits of bone, during a Danish-led excavation in 1986. They were placed in a plastic bag, filed away in Denmark's National Museum, and largely forgotten about. When Willerslev heard about the hair, he could hardly believe his luck.

Researchers handled the hairs carefully to reduce the risk of contamination, and verified that only Europeans had come in contact with the samples. That was important, because they wanted to minimize the chance that modern-day DNA would get in the way of the big question they were aiming to answer.

Tale of an extinct culture
Archaeological studies had determined that the hair and bone came from an individual of the Saqqaq culture, a now-extinct people who were among Greenland's earliest residents. Anthropologists have long wondered whether the Saqqaq were the descendants of "First Americans" who crossed the Bering land bridge from Siberia 10,000 to 14,000 years ago - or whether they were part of a different migration.

Once Inuk's DNA was analyzed, researchers could compare his code to that of present-day groups ranging from the Inuit to Native Americans to Siberians.

"The closest contemporary population he is associated with is in fact not Inuits or Greenlanders or Native Americans in the New World, but three Siberian populations," Willerslev said. And when the team looked more closely at the DNA comparison with those three groups - the Nganasans, Koryaks and Chukchis - they determined that Inuk's ethnic group probably split off a mere 5,500 years ago.

That suggests that Inuk and his kin came to America during a previously unknown wave of migration. At that time, the Bering land bridge didn't exist, so Willerslev and his colleagues assume that the migrants must have crossed either by sea or over winter ice.

The reasons why the Saqqaq eventually faded into oblivion remain shrouded in mystery. They might have been assimilated or pushed into extinction by later cultures, such as the Dorset or Thule peoples. Willerslev said follow-up genetic studies could shed further light on that question.

Fleshing out Inuk's portrait
The researchers were interested not only in the big picture, but also in a portrait of the individual behind the DNA. Because the genetic readings were so detailed, they could use bits of coding known as single-nucleotide polymorphisms (better known as SNPs, or "snips") to link Inuk's genome to modern-day genetic traits.

The results confirmed Inuk's Siberian background in surprisingly detailed ways:

  • His blood type was A+, which is found in very high frequency in east Asian populations.
  • Combinations of SNPs suggest that he had brown eyes as well as dark, thick hair and a skin color that was not as light as that commonly found in Europeans.
  • One of the SNPs is linked to shovel-graded front teeth, a characteristic trait of Asian and Native American populations.
  • Another SNP is linked to having earwax of the dry type that is typical of Asians and Native Americans, rather than the "wet" earwax found in other ethnic groups.
  • A 12-SNP combination, linked to metabolism and body mass index, suggests that Inuk was adapted to a cold climate.
  • Inuk's genetic code also indicates that he had an increased risk of baldness. The fact that Inuk's hair could be recovered thousands of years later led Willerslev to suggest half-jokingly that "he actually died quite young."

Inuk's hair turned out to be a genetic jackpot, thanks to the fact that it was so well-preserved and free of modern-day contamination. If there were significant contamination, the researchers assumed it would show up as a European genetic signature, because the samples were handled exclusively by European researchers. By that measure, the maximum estimated contamination was 0.8 percent, "not much higher than background," Willerslev said.

Willerslev and other geneticists conceded that few ancient samples from elsewhere in the world could come up to Inuk's standard. Rubin said the preservative qualities of the permafrost couldn't be underestimated. "It's like putting a piece of meat in your freezer rather than on your kitchen table," he told me. "This is a great sample for that reason."

But the geneticists also said sequencing techniques were improving so much, for ancient as well as present-day DNA, that other long-dead cultures could be studied in the future. What skin color did the ancient Egyptians have? What genetic diseases afflicted the Etruscans? How did humans settle the Americas?

Willerslev said "only time can show" if the technique used on Inuk's hair can be applied to other genetic samples from ancient human remains. "But honestly speaking, I think it is very likely that you can," he said.


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