This is a question about human population genetics and human prehistory that has implications well beyond the Americas, because it touches on the deep history of how different human populations diverged from each other in Asia and how those divergence patterns were subsequently shuffled as populations moved and mixed.

What Is Not Known and Why It Matters

The honest summary of where the Population Y debate stands is that the signal is real, its explanation is not definitively known, and the resolution of the debate will require data and methods that are not yet available.

What is known: Some ancient and modern South American populations show statistically significant excess allele sharing with Australasian populations.

The signal is strongest in certain parts of South America and weaker or undetectable in others.