But it is also the model that is most difficult to test directly, because it requires characterizing the genetic diversity of ancient Beringian and northeastern Asian populations at a time period and geographic scale for which the ancient DNA evidence is sparse.

The Turnover Question Revisited at Continental Scale

The genomic picture of the Americas is, at continental scale, one of remarkable complexity.

The earliest Native Americans — the descendants of the founding Beringian population — spread across two continents in a geologically brief period.

As they spread, they differentiated genetically, adapting to different environments, experiencing different local population histories, and establishing the diverse genetic profiles that characterize Native American populations today.

Overlaid on this initial differentiation is a complex history of subsequent contact, admixture, and in some cases dramatic population change.