First ancient human sequenced
For the first time researchers have sequenced an ancient human genome, revealing characteristics of Greenland's first inhabitants and providing evidence of a previously unknown human migration, according to a study published in this week's Nature.
Artist rendition of ancient Saqqaq Image: Nuka GodfredtsenPast studies have sequenced partial genomes or mitochondrial DNA, which only codes for the mother's side of the genome, said linkurl:David Lambert,;http://www.griffith.edu.au/environment-plan
For the first time researchers have sequenced an ancient human genome, revealing characteristics of Greenland's first inhabitants and providing evidence of a previously unknown human migration, according to a study published in this week's Nature
Artist rendition of ancient Saqqaq
Image: Nuka Godfredtsen
Past studies have sequenced partial genomes or mitochondrial DNA, which only codes for the mother's side of the genome, said linkurl:David Lambert,;http://www.griffith.edu.au/environment-planning-architecture/griffith-school-environment/staff/professor-david-lambert an evolutionary biologist from Griffith University who was not involved in the study. "But this is really the first complete ancient human genome."
"This research brings new excitement to the field because it shows us that we can potentially reconstruct not only where people came from, but also what they looked like," said Lambert, who wrote an accompanying commentary to the study in Nature
. This level of reconstruction is possible, he explained, because the Human Genome Project has provided extensive databases with which to compare this ancient individual's genome.
Researchers from the University of Copenhagen and an international team of collaborators used hair belonging to a 4,000-year-old Saqqaq (the first known inhabitants of Greenland) that had been preserved in the permafrost. They employed the latest next-generation sequencing technologies to a depth of 20x, meaning on average they sequenced the genome 20 times. "The greater depth you get, the more security you get on the accuracy of each base," linkurl:Eske Willerslev,;http://www1.bio.ku.dk/english/staff/profile/?id=26558 an evolutionary geneticist at the University of Copenhagen and senior author on the paper, told The Scientist
. "In principle it allows you to get a genome that is as good quality as a modern human genome."
The researchers identified more than 350,000 single-nucleotide polymorphisms (SNPs) - single DNA base pair differences between individuals. When they compared the ancient Greenlander's SNPs to the genomes of individuals in several surrounding populations, they found he was most closely related to Old World Arctic populations of the Siberian Far East. Moreover, his ancestors diverged from their Siberian relatives roughly 200 generations, or 5,500 years ago.
These results suggest a substantial and recent migration across the Bering Strait, independent of the one that gave rise to modern Inuit and Native American populations, Willerslev said. He further noted that these results are likely not an isolated case. "If we start screening ancient samples, both from the Americas and other places in the world, I think we will come up with many surprises," Willerslev said. "And I think that you will see there have been migrations that didn't leave behind any contemporary decedents."
Willerslev is not alone in this idea. "The models that suggest a single one-time migration are generally regarded as idealized systems, like an idealized gas in physics," said linkurl:Marcus Feldman,;http://www-evo.stanford.edu/marc.html a population geneticist at Stanford University who was not involved with the study. "But there may have been small amounts of migrations going on for millennia." Just because researchers put a date on when ancient humans crossed the Bering Bridge, that doesn't mean it happened only once and then stopped, he said.
Based on their analysis of the SNPs, the researchers were not only able to detect the ancient Saqqaq's geographical origins, but also determine many of his traits. They found that he was an inbred male, with A-positive blood, brown eyes, non-white skin, thick dark hair, and shovel-graded front teeth typical of Asian and Native American populations. They further showed that he had an increased susceptibility to baldness, dry earwax, and a metabolism and body-mass index comparable to humans living in cold climates.
Lambert stressed, however, that the study's success relied on access to an extraordinary sample. "This is an ideal sample of hair, which is very good for preservation of DNA; it's exactly the right kind of tissue and was found in exactly the right kind of environment," he said. "The real 64-dollar question will be: What happens when we start to look at things from temperate or even hot environments where the survival and recovery of DNA is much lower?"
Willerslev said he's optimistic that other samples will provide the DNA fragments needed for similar sequencing efforts. In their next project, the researchers will sequence DNA from hair samples of mummies gathered throughout South America, some of which date back 8,000 years and could lend insight into early migration into the Americas.
This ancient Saqqaq was their first sample and represented such a short historical time period - 5,500 years - and already provided evidence of a new migration, Willerslev noted. "Think about what could happen in the Americas where you have a period of 12,000-14,000 years or potentially even longer," he said. "It's a long time period and opens up the possibility for a lot of stuff happening."
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[18th January 2010]*linkurl:Ancient iceman has no modern kin;http://www.the-scientist.com/blog/display/55145/
[30th October 2008]*linkurl:Hair yields ancient DNA;http://www.the-scientist.com/news/home/53656/
[27th September 2007]