Indigenous Americans descend from people who crossed an ancient land bridge connecting Siberia to Alaska thousands of years ago. Two new studies reveal the most closely related Native American ancestor outside North America.
     In the first study, researchers sequenced the genomes of 34 individuals who lived in Siberia, the land bridge Beringia, and Alaska from 600 to nearly 32,000 years ago. The oldest individuals in the sample - two men who lived in far northern Siberia - represent the earliest known humans from that part of the world. There are no direct genetic traces of these men in any of the other groups the team surveyed, suggesting their culture likely died out about 23,000 years ago when the region became too cold to be inhabitable.
     However, DNA analysis reveals that elsewhere on the Eurasian continent a group arose that would eventually cross Beringia into North America. A woman who lived in northeastern Siberia about 10,000 years ago known as Kolyma 1 (named after a region in the Russian Far East), shares about two-thirds of her genome with living Native Americans. Based on the time it would have taken for key mutations to occur, the ancestors of today's Native Americans diverged from these ancient Siberians about 24,000 years ago.
     Additional DNA evidence suggests a third wave of migrants moved into northeastern Siberia from the south sometime after 10,000 years ago. These mixed with the ancient Siberians, forming many of the area's present-day populations.
     In the second study, researchers attempted to uncover the roots of a genetic family known to scientists as Paleo-Eskimos. Originating in Siberia and crossing Beringia about 5000 years ago, they mixed with both a previous wave of Siberian migrants as well as a much later lineage called Neo-Eskimos. Their descendants are the modern native speakers of Na-Dene and Eskimo-Aleut languages.
     The scientists analyzed the genomes of 48 individuals from sites in the North American Arctic and Siberia dating from between about 7000 to 300 years ago, comparing their DNA to those of other modern and ancient Indigenous people across northern North America, looking for shared ancestry and language families. Based on their analysis, the group from whom Kolyma 1 descended may be the ancestors or very close relations of the Paleo-Eskimos.

Edited from Science Magazine (5 June 2019)