This pattern of uneven distribution — some Amazonian populations carrying the signal and others not — is consistent with either a model in which a Population Y-related founding group settled some parts of the Amazon basin but not others, or a model in which the founding Beringian population contained structured diversity that was differentially distributed as different founding lineages settled different parts of the continent.

The specific demographic history of the Amazon basin is relevant to distinguishing between these models.

If the genetic analysis shows that the Amazonian populations with the strongest Population Y signal are also the populations that show the most evidence of deep genetic ancestry — the most continuity with early settlement and the least evidence of later genetic mixing from populations without the signal — then the deep ancestral structure model is supported.

If the signal appears to have been introduced into some Amazonian populations at a specific time that can be dated genetically, and if that time is consistent with a demographic event in the region’s history, then an admixture model is more plausible.