The ancestral population that gave rise to all Native Americans — sometimes called the “First Peoples” or the “Ancestral Native American” population — spent an extended period in the Beringia region before the genetic and archaeological evidence suggests they dispersed into the Americas, probably around 16,000 to 20,000 years ago, though the exact timing and the question of one versus multiple dispersal events continues to be debated.

Here is the key question: what was the deep structure of the ancestral Beringian population before it entered the Americas?

If the population that eventually crossed into the Americas was itself genetically diverse — if it contained subgroups or lineages that had different amounts of ancestry from different ancient Asian populations, including populations related to the southern-route dispersal toward Australia — then those differences in ancestry would have been preserved in different proportions in different descendant populations as they spread across the Americas.

This model — deep ancestral structure within the founding population — can produce the Population Y signal without requiring any migration from Australia to the Americas.