"One unanswered question is why the Y signal hasn’t turned up in any North or Central American Indigenous groups. One possibility, Hünemeier suggests, is that the Y signal–bearing migrants simply stuck to the coast and made it to South America without leaving any genetic legacy up north"
Ok. But how about "Or they arrived on the shores of South America by boat" ? I don't understand why that hypothesis seems to be avoided? It seems much more credible than "the people with that particular genetic legacy hugged the coast all the way down to So America and didn't mix with any other groups along the way."
They did leave a genetic legacy up north in ancient remains like Anzick-1 and ancient Channel island remains [1]. That legacy simply no longer exists among most remaining native populations in the US and Canada. Moreover, they're still clearly related to North American natives, it's just a more distant relationship. So it's not that North Americans and South/Central Americans descend from different ancestral populations, the population structure is just poorly understood.
I wouldn't go that far. We're talking wildly different timescales. Migration to the Americas over the Bering was < 16,000 years ago, while the golden age of Polynesian exploration was only about 1,000-2,000 years ago.
