NEW YORK (GenomeWeb News) – For the first time, researchers have sequenced the entire mitochondrial genome of an ancient human and, in so doing, have gotten a unique glimpse into the history of early populations living in the far North.
In a paper published online today in Science Express, researchers from the University of Copenhagen and elsewhere extracted and decoded mitochondrial DNA from a mass of human hair that had been hidden in Greenland’s permafrost for thousands of years. The results suggest that the Saqqaq, the earliest known culture in Greenland and the extreme American North, were not related to present day Native Americans or Greenlanders. Rather, the group appears to have originated from islands in and around the Bering Sea.
“The Saqqaq probably weren’t Native Americans and they probably weren’t the ancestors of modern Greenlanders,” lead author Tom Gilbert, an evolutionary biologist at the University of Copenhagen, told GenomeWeb Daily News today.
There is evidence that humans lived in Greenland and the New World’s distant north at least 4,000 years ago. Since then, there have been distinct populations of ancient humans, termed “Paleo-Eskimos,” in this region at different moments in history. But for the most part these cultures are known only from cultural artifacts excavated in the North, Gilbert explained. Consequently, there has been heated debate over how many times people populated the North and where each of these populations originated.
For instance, some speculated that the Saqqaq were related to Native Americans, while others thought they were related to the Siberian population that gave rise to modern Greenlanders, Gilbert said. Still others believed the group was distinct from both Native Americans and Siberians.
Adding to the mystery was the fact that no Saqqaq human remains were discovered in Northern Canada or Greenland. That changed in the 1980’s, when a handful of bones and a clump of human hair — preserved in permafrost for some 3,400 to 4,500 years — was discovered in the Disko Bay fjords in the north-west part of Greenland. But the bones were poorly preserved, Gilbert said, and it took several years before researchers turned their attention to the soda can-sized chunk of hair.
Initial experiments suggested that the samples hadn’t been contaminated by modern human DNA. Rather, based on the mitochondrial hypervariable sequence, the Saqqaq individual appeared to be unrelated to modern European and Greenland Inuit populations.
Although there was some DNA fragmentation in the hair sample, Gilbert said, there was enough DNA to do genetic analysis. For this study, Gilbert and his colleagues sequenced the entire mitochondrial genome to about 10.7 times coverage using 454 Life Sciences’ FLX sequencing-by-synthesis method.
Overall, the researchers noted that the Saqqaq mitochondrial genome differed from the latest Cambridge Reference Sequence at 40 SNPs. Although some of these seem to represent damaged DNA, most seemed to correspond to genuine sequence differences. The sequence also contained a previously unrecognized heteroplasmic site.
To get a better idea of how the ancient Saqqaq individual was related to living populations, if at all, the team compared the mitochondrial sequence with those from other populations. To do this, they sequenced mtDNA from 14 modern Greenlanders and relied on available sequence data for other populations, such as Native Americans and northeast Asians.
Based on this comparison, Gilbert and his colleagues concluded that the Saqqaq haplogroup was different from that of Native Americans and from that of the so-called “Neo-Eskimo” populations living in the far North for the last 1,000 years or so.
“It’s never been observed in Native Americans and it’s never been observed in Greenlanders,” Gilbert said. “It’s a completely different mitochondrial group.”
Gilbert was quick to acknowledge the possibility that the groups are related and that present day Native Americans or Greenlanders have lost the Saqqaq genetic signature. But, based on the information available at this time, the ancient Saqqaq individual seems to be most closely related to Aleut populations in the Commander Islands and a sub-set of the Sireniki Yuit, a population in Siberia.
Even so, Gilbert noted, it’s difficult to draw firm conclusions about entire populations based on one individual. And because the team looked strictly at mitochondrial sequence for this study, it can only predict Saqqaq maternal lineage. In the future, the group plans to do further genetic analysis, including Y chromosome sequencing that will give them a better handle on Saqqaq paternal lineage as well.