The first humans in North America arrived from Asia some time before
14,500 years ago. The next major stream of gene flow came about 5000
years ago, and is known to archaeologists as Paleo-Eskimos. About 800
years ago, the ancestors of the present-day Inuit and Yup'ik people
replaced this population across the Arctic. By about 700 years ago, the
archaeological evidence for the Paleo-Eskimo culture disappeared. Their
genetic legacy in living populations has been contentious, with several
genetic studies arguing that they made little contribution to later
North Americans.
In the current study, researchers generated genome-wide data from 48
ancient individuals and 93 modern individuals from Siberia, Alaska, the
Aleutian Islands and Canada, and compared this with previously
published data. The researchers used novel analysis methods to create a
comprehensive model of population history that included many ancient and
modern groups to determine how they might be related to each other.
"Our study is unique, not only in that it greatly expands the number of
ancient genomes from this region, but because it is the first study to
comprehensively describe all of these populations in one single coherent
model," states Stephan Schiffels of the Max Planck Institute for the
Science of Human History.
Paleo-Eskimos left a lasting legacy that extends across North America
The researchers were able to show that a substantial proportion of
the genetic heritage of all ancient and modern American Arctic and
Chukotkan populations comes from Paleo-Eskimos. This includes people
speaking Eskimo-Aleut languages, such as the Yup'ik, Inuit and Aleuts,
and groups speaking Na-Dene languages, such as Athabaskan and Tlingit
speakers, in Canada, Alaska, and the lower 48 states of the United
States.
Based on the researchers' analysis, Paleo-Eskimos interbred with
people with ancestry similar to more southern Native peoples shortly
after their arrival to Alaska, between 5,000 and 4,000 years ago. The
ancestors of Aleutian Islanders and Athabaskans derive their genetic
heritage directly from the ancient mixture between these two groups. The
researchers also found that the ancestors of the Inuit and Yup'ik
people crossed the Bering Strait at least three times: first as
Paleo-Eskimos to Alaska, second as predecessors of the Old Bering Sea
archaeological culture back to Chukotka, and third to Alaska again as
bearers of the Thule culture. During their stay in Chukotka that likely
lasted for more than 1000 years, Yupik and Inuit ancestors also admixed
with local groups related to present-day Chukchi and local peoples from
Kamchatka.
Paleo-Eskimo ancestry is particularly widespread today in Na-Dene
language speakers, which includes Athabaskan and Tlingit communities
from Alaska and northern Canada, the West Coast of the United States,
and the southwest United States.
"For the last seven years, there has been a debate about whether
Paleo-Eskimos contributed genetically to people living in North America
today; our study resolves this debate and furthermore supports the
theory that Paleo-Eskimos spread Na-Dene languages," explains David
Reich of Harvard Medical School and the Howard Hughes Medical Institute.
"One of the most striking case examples from our study is the ancient
DNA we generated from the ancient Athabaskan site of Tochak McGrath in
interior Alaska, where we worked in consultation with the local
community to obtain data from three approximately seven hundred year old
individuals. We found that these individuals, who lived after the time
when the Paleo-Eskimo archaeological culture disappeared across North
America, are well modeled as a mixture of the same two ancestry
components as those found in Athabaskans today, and derived more than
40% of their ancestry from Paleo-Eskimos.
A case example for how genetics can be combined with archaeology to shed new light on the past
The researchers hope that the paper will provide an example of the
value of genetic data, in the context of archaeological knowledge, to
resolve long-standing questions.
"Determining what happened to this population was not possible from
the archaeological record alone," explains Pavel Flegontov of the
University of Ostrava. "By analyzing genetic data in concert with the
archaeological data, we can meaningfully improve our understanding of
the prehistory of peoples of this region. We faced challenging
analytical problems due to the complex sequence of gene flows that have
shaped ancestries of peoples on both sides of the Bering Strait.
Reconstructing this sequence of events required new modelling approaches
that we hope may be useful for solving similar problems in other
regions of the world."
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