Researchers have reconstructed an ancient human genome for the first time, thanks to the discovery of a 4000-year-old clump of hair in Greenland permafrost. Experts say that similar techniques could be employed in many other ways, such as analyzing the DNA of South American mummies or crime victims.
The sample was taken from one of four clumps of hair collected in Greenland by Danish archaeologists in the 1980s. The hairs--found tangled around a whale bone comb--are the only known human remains from the earliest people to settle in Greenland, known as the Saqqaq culture. A chance conversation alerted University of Copenhagen researcher Eske Willerslev, who was just back from two unsuccessful months in Greenland searching for human remains to test for DNA, to the sample, which had been stored at the National Museum of Denmark for more than 20 years.
Once they had the hairs in their possession, Willerslev and colleagues set about sequencing the sample. The team used dozens of sequencing machines to identify and map DNA fragments in the hair shafts, a process that took nearly 2 months. The data revealed more than 80%% of the genome, coverage comparable to what can be done with a modern human genome.
"From the DNA, we can tell a lot about the individual," says Willerslev. "He had brown eyes, brown skin, a tendency to baldness, dry earwax, and shovel-shaped front teeth." The researchers have named him "Inuk," which means "man" or "human" in Greenlandic.
The genome also sheds light on where the man's relatives came from. When the researchers compared his DNA with that collected from more than 40 Arctic and native North American populations, they concluded that the first people to settle in Greenland were related to groups now living in northeastern Siberia like the Chukchi and Koryak. The analysis also revealed that these first colonists were not the ancestors of the Inuit who live on the island now.
Willerslev and colleagues, who report their findings tomorrow in Nature, went to great lengths to show that the sample was not contaminated by modern DNA--a concern because the hair had been handled by archaeologists and stored in a museum. Hair, which is nonporous, is ideal: "All the contamination is on the surface, so it's quite easy to get rid of," says Morten Rasmussen, another researcher on the team.
To verify that the sample was contamination-free, the researchers looked for traces in the genetic code of genes that appear only in European populations. They found none, showing that the DNA inside the hair shaft was pure. "They did everything they could to show the sequence was good," says Beth Shapiro, a biologist at Pennsylvania State University, University Park. "It's a beautiful sample."
Colleagues say that when it comes to ancient DNA, the Greenland sample may amount to low-hanging fruit. The hair had been preserved by cold for thousands of years, ideal conditions for recovering DNA. "Working with these young permafrost samples--whether bone or hair--is worlds apart from working with older, non-permafrost samples," says Adrian Briggs, a researcher at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. He notes that the Greenland sample contains tens of thousands of times more DNA than typically found inNeandertal and early modern human samples from warmer environments.
Yet the discovery shows that with ever-cheaper genetic sequencing and faster computers, it is possible to recover a full nuclear DNA sequence from an ancient human, even when the genome is broken into tiny fragments. "The nicest thing this paper shows is that the application of next-generation sequencing techniques is really going to expand what we can do with ancient DNA," says Shapiro.