The Competing Models That Remain

The 2018 USR1 paper proposed a specific two-branch model for the founding of the Americas, with the Ancient Beringian branch diverging before the southward expansion of the main First American branch.

This model has been incorporated into subsequent work, but it has also been questioned and refined.

One significant complication comes from the evidence for pre-Clovis human presence in the Americas — specifically the White Sands footprints, dated to approximately 21,000 to 23,000 years ago.

If people were in the interior of North America during the Last Glacial Maximum, they must have been there before the Ancient Beringian / First American divergence that the 2018 model places at approximately 20,000 years ago.