The genetic prehistory of the New World Arctic

Introduction Humans first peopled the North American Arctic (northern Alaska, Canada, and Greenland) around 6000 years ago, leaving behind a complex archaeological record that consisted of different cultural units and distinct ways of life, including the Early Paleo-Eskimos (Pre-Dorset/Saqqaq), the Late Paleo-Eskimos (Early Dorset, Middle Dorset, and Late Dorset), and the Thule cultures. Genetic origins of Paleo-Eskimos and Neo-Eskimos. All Paleo-Eskimos represent a single migration pulse from Siberia into the Americas, independent of the Neo-Eskimo Thule people (ancestors of modern-day Inuit) and the related extinct Sadlermiut population. The Siberian Birnirk people were likely cultural and genetic ancestors of modern-day Inuit. We also show ancient admixture between the Paleo- and Neo-Eskimo lineages, occurring at least 4000 years ago. Rationale We addressed the genetic origins and relationships of the various New World Arctic cultures to each other and to modern-day populations in the region. We obtained 26 genome-wide sequences and 169 mitochondrial DNA sequences from ancient human bone, teeth, and hair samples from Arctic Siberia, Alaska, Canada, and Greenland, and high-coverage genomes of two present-day Greenlandic Inuit, two Siberian Nivkhs, one Aleutian Islander, and two Athabascan Native Americans. Twenty-seven ancient samples were radiocarbon dated for accurate cultural assignment, of which 25 were corrected for marine reservoir effect to account for the dominant marine component in these individuals’ diets. Results Nuclear and mitochondrial DNA data unequivocally show that the Paleo-Eskimos are closer to each other than to any other present-day population. The Thule culture represents a distinct people that are genetic and cultural ancestors of modern-day Inuit. We additionally find the Siberian Birnirk culture (6th to 7th century CE) as likely cultural and genetic ancestors of the Thule. The extinct Sadlermiut people from the Hudson Bay region (15th to 19th century CE), considered to be Dorset remnants, are genetically closely related to Thule/Inuit, rather than the Paleo-Eskimos. Moreover, there is no evidence of matrilineal gene flow between Dorset or Thule groups with neighboring Norse (Vikings) populations settling in the Arctic around 1000 years ago. However, we do detect gene flow between the Paleo-Eskimo and Neo-Eskimo lineages, dating back to at least 4000 years. Conclusion Our study has a number of important implications: Paleo-Eskimos likely represent a single migration pulse into the Americas from Siberia, separate from the ones giving rise to the Inuit and other Native Americans, including Athabascan speakers. Paleo-Eskimos, despite showing cultural differences across time and space, constituted a single population displaying genetic continuity for more than 4000 years. On the contrary, the Thule people, ancestors of contemporary Inuit, represent a population replacement of the Paleo-Eskimos that occurred less than 700 years ago. The long-term genetic continuity of the Paleo-Eskimo gene pool and lack of evidence of Native American admixture suggest that the Saqqaq and Dorset people were largely living in genetic isolation after entering the New World. Thus, the Paleo-Eskimo technological innovations and changes through time, as evident from the archaeological record, seem to have occurred solely by movement of ideas within a single resident population. This suggests that cultural similarities and differences are not solid proxies for population movements and migrations into new and dramatically different environments, as is often assumed. Arctic genetics comes in from the cold Despite a well-characterized archaeological record, the genetics of the people who inhabit the Arctic have been unexplored. Raghavan et al. sequenced ancient and modern genomes of individuals from the North American Arctic (see the Perspective by Park). Analyses of these genomes indicate that the Arctic was colonized 6000 years ago by a migration separate from the one that gave rise to other Native American populations. Furthermore, the original paleo-inhabitants of the Arctic appear to have been completely replaced approximately 700 years ago. Science, this issue 10.1126/science.1255832; see also p. 1004 Early Arctic humans differed from both present-day Inuit and Native Americans. [Also see Perspective by Park] The New World Arctic, the last region of the Americas to be populated by humans, has a relatively well-researched archaeology, but an understanding of its genetic history is lacking. We present genome-wide sequence data from ancient and present-day humans from Greenland, Arctic Canada, Alaska, Aleutian Islands, and Siberia. We show that Paleo-Eskimos (~3000 BCE to 1300 CE) represent a migration pulse into the Americas independent of both Native American and Inuit expansions. Furthermore, the genetic continuity characterizing the Paleo-Eskimo period was interrupted by the arrival of a new population, representing the ancestors of present-day Inuit, with evidence of past gene flow between these lineages. Despite periodic abandonment of major Arctic regions, a single Paleo-Eskimo metapopulation likely survived in near-isolation for more than 4000 years, only to vanish around 700 years ago.