Genetic analysis of Native American populations suggests that the founding population was isolated from other Asian populations for a period before the dispersal into the Americas — a period of isolation long enough to allow the founding population to accumulate genetic variants that are distinct from the source populations in Asia.

Modeling of the genetic data suggests an isolation period of roughly 2,000 to 9,000 years, though the uncertainty in these estimates is large.

The geographic context of this isolation was Beringia — the landmass that connected northeastern Asia to northwestern North America when sea levels were lower during the Last Glacial Maximum.

Beringia was not the frozen wasteland that the name might suggest; during the Last Glacial Maximum, it was a landscape of shrub tundra and grassland, with a more temperate climate than the areas immediately to its south and east where the great ice sheets covered much of North America.

The Beringian environment could have supported a human population, and the evidence suggests that it did.