Thanks to new sequencing technologies, and a few tufts of
hair rescued from a museum basement, researchers have reconstructed the genome
sequence of a man who lived in western Greenland about 4000 years ago. Researchers
from the University of Copenhagen were able to read about 80 percent of his genome
at a level of accuracy comparable to the genome sequences of living people. (Only
eight human genome sequences have been published to date.)
An artist’s impression of “Inuk,” an ancient Eskimo whose genome has been sequenced.
Credit: Nuka Godfredsen
That level of accuracy allowed scientists to analyze 350,000
single nucleotide polymorphisms, or SNPs–spots of common genetic variation
within the genome–enabling them to draw conclusions about both the physiology
of the man and his origins.
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According to a commentary accompanying the paper in Nature,
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“he
had an A+ blood group, brown eyes, non-white skin, thick dark hair and
‘shovel-graded’ front teeth typical of Asian and Native American populations. What’s
more, he had an increased susceptibility to baldness, dry earwax and a
metabolism and body-mass index commonly found in those who live in cold
climates.”
By comparing the SNP data with that of several
surrounding populations, researchers were able to pinpoint his geographical
origin.
Surprisingly, the
ancient eskimo proved to be most closely related to three Old World Arctic populations:
the Nganasans, Koryaks and Chukchis of the Siberian far east. This suggests that
there was a substantial and relatively recent migration across the Bering
Strait and over North America to Greenland. The authors’ analysis indicates that
the Saqqaqs diverged from the Chukchis about 200 generations (5,400 years) ago,
implying that the ancestral Saqqaqs separated from their Old World relatives
almost immediately before their migration to the New World.
Scientists
had previously analyzed DNA from Neandertal bone and tooth samples, but not to this level of accuracy. Sequencing
ancient DNA samples is notoriously difficult, thanks to degraded DNA and
contamination from bacteria, fungus and humans handling the samples. In this
case, researchers say only Europeans handled the DNA, and the sample itself was
found to have no European ancestry. They used sequencing technology from the company Illumina.
According to the New York Times, the hair, originally dug out of the
permafrost at Qeqertasussuk on the west coast of Greenland in 1986, was kept in
a plastic bag in the National Museum of Denmark. It was found
with other waste, and the scientists speculate that it was the result of a
haircut.
“There it moldered, unfrozen, until discovered by Dr. Willerslev, an expert
on ancient DNA. Having spent two months digging for ancient human DNA in
Greenland without finding any human remains, he concluded that ancient
Greenlanders must have disposed of their dead by laying them on the sea ice.
Only on complaining of his bad luck to a friend did he learn that the friend’s
father had found the hair sample 20 years earlier.”
