The founding populations of the Americas — the people who crossed from Asia into what is now Alaska during the terminal Pleistocene, as the great ice sheets were at their maximum extent and sea levels were at their lowest, exposing the Bering Land Bridge — were a distinct lineage that had diverged from other east Asian populations and spent a period of time in geographic isolation before spreading southward.

During this isolation, which some researchers have called the Beringian standstill, the founding population accumulated genetic distinctiveness that sets it apart from any other human group on Earth.

Once these founding populations began moving southward and spreading across the Americas, their genomes diversified.

Regional populations developed genetic characteristics that differed from other regional populations, shaped by genetic drift — the random changes that occur when populations are separated and small — and by the specific selection pressures of different environments.

But the fundamental story encoded in modern Native American genomes points to a primary origin in northeast Asia, a period of isolation in or near Beringia, and a relatively rapid spread southward once the continental ice sheets began their final retreat.