One of the most informative aspects of the Population Y signal is its geographic distribution within the Americas — the fact that it is found at significantly different intensities, or not at all, in different Native American populations.

The signal is strongest in certain populations from the Amazon basin, in some populations from Brazil more broadly, and in some populations from the Pacific coast of South America.

It is weaker or undetectable in many North American populations, in populations from the Caribbean, and in many populations from the southern cone of South America.

This geographic pattern is itself evidence that can help distinguish between different models of the signal’s origin.

A model in which a separate Australasian-related population migrated to South America and mixed with the founding Native American population would predict that the signal should be strongest in the geographic area where that mixing occurred and should decrease with distance from that area.