The geographic distribution of the signal is broadly consistent with this prediction, in the sense that it is concentrated in the parts of South America closest to the Pacific — the ocean that would have to be crossed if there were a direct connection to Australasian populations.

But the geographic distribution also poses challenges for simple migration models.

If a population related to Australasians reached South America by crossing the Pacific, that crossing would have been extraordinarily difficult with the technology available to human populations in the early Holocene.

The Pacific Ocean is vast.

No human population is known to have made sustained trans-Pacific crossings before the Polynesian expansion, which occurred within the past two to three thousand years — far too recently to account for a signal in populations that were already present in South America ten to twelve thousand years ago.

Some researchers have proposed a coastal route model — the idea that a population related to Australasians could have reached the Americas by following a coastal route along the edge of Asia, through Beringia, and then down the Pacific coast of North and South America, rather than by crossing the open Pacific directly.