A new study, published in Science, shows that the first people to populate the Arctic regions of North America and Greenland were a group who moved into the area from Siberia around 3,000 B.C. They lived in isolation for almost 4,000 years, before disappearing.

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Previous research has indicated that there were three waves of migration from Asia to the New World; this new study adds a fourth. The first humans are thought to have crossed over the Bering Strait more than 15,000 years ago; this new wave of Paleo-Eskimos, which brought the first people to spread across the northern reaches of Alaska, Canada and Greenland, would have come after the first two waves, but before the Neo-Eskimo or Thule made the journey between continents.

Archaeologically, people living in the North American Arctic between approximately 2,500 B.C. and 1,000 A.D. are referred to as the Dorset and Pre-Dorset cultures. (They're classified into those based on the tools and artwork they left behind.) This new study shows that not only did this group have different traditions and culture from the area's later populations but it was genetically distinct from them, as well.

That lack of genetic mixing was a huge surprise, said Eske Willerslev, an evolutionary biologist and co-author of the study, in a press conference. “In other studies, when we see people meeting each other, they might be fighting each other, but normally they actually also have sex with each other. And that doesn’t really seem to have been the case here, and they must have been coexisting for thousands of years,” Willerslev said.

The Paleo-Eskimo people lived in small villages (populations of just 20 to 30) scattered across the Arctic, said Bill Fitzhugh, another co-author and an archaeologist at the National Museum of Natural History. In order for these societies to survive for 4,000 years in isolation, he suggested, they must have been very traditional—extremely connected to the land and the resources they used to survive. “One might almost say, kind of jokingly and very informally, that the Dorsets were the hobbits of the Eastern Arctic, a very strange and very conservative people that we're only just getting to know a little bit,” Fitzhugh says.

After surviving in isolation for nearly 4,000 years, the Paleo-Eskimo/Dorset people vanished around 1,300 A.D., within the space of just 100 to 150 years. Researchers still have no idea how exactly they disappeared—whether it was violence, disease or some unknown factor that wiped them out. They were replaced by the Thule people, who had developed larger boats, more advanced weapons and the ability to hunt whales. Genetic evidence collected in this study indicates that modern Inuit peoples are descended from the Thule and not from the Paleo-Eskimo groups.