If that ancestry was not uniformly distributed within the founding population — if some lineages had more and some had less — then the differential distribution of those lineages across descendant populations could produce the population Y signal.

This model does not require Australasians to have traveled to Asia and mixed with the founding Native American population at the time of American settlement.

It requires only that the ancient Asian populations that contributed to the founding Native American population included groups that had retained more “Australasian-related” ancestry from the deep human past — ancestry that was part of the shared human heritage of the populations that spread out of Africa along the southern route tens of thousands of years before the Americas were settled.

This deep ancestry model is perhaps the most parsimonious explanation of the Population Y signal available — it requires fewer specific historical events than models that involve separate migrations, and it is consistent with the overall picture of human population history that the genomic evidence from Asia, the Americas, and Australasia has produced.