The Ancient Beringian lineage — the one represented by USR1 — was apparently one of these groups that became isolated early, before the main southward expansion began.

The specific geographic and demographic circumstances that led to this isolation are not recoverable from the single genome of USR1.

Was it a matter of the Ancient Beringians occupying a specific ecological niche or geographic territory that kept them separate from the proto-First American population?

Was it a matter of the two groups being simply far enough apart that regular interbreeding was limited?

Was it a matter of the specific movement patterns of different groups across the Beringian landscape?