[irrational]

What is the reasoning for thinking they came from the top? You’ve said they had already reached Australia via boat. Couldn’t they have reached some other part of the Americas by boat, maybe South America via Africa or Easter island?

[miniwark]

Mainly because both Americas where inhabited way before the pacific islands. For example Easter Island is estimated to have been inhabited around 300 to 1200 CE. This is also confirmed by genetics, with an origin of the Amerindians located around central Siberia.

See https://en.wikipedia.org/wiki/Genetic_history_of_Indigenous_...

[irrational]

Someone else posted this farther down, but you might not see it. Apparently there is some proof that they also have ancestry from Australia.

https://www.smithsonianmag.com/science-nature/dna-search-fir...

[AlotOfReading]

We've definitively established that Clovis populations and all modern Native Americans are genetically related to Beringian populations out of Eurasia. It's reasonable to suspect pre-clovis populations probably came from much the same area, especially given that suggested pre-clovis lithics so closely resemble clovis traditions.

Additionally, the farthest east that we've found evidence of Australasian populations is the Solomon islands, some 7,000+ mi from South America. There's no evidence of habitation on the intervening islands until Austronesian peoples show up much later. As for Africa, we simply have no evidence for it whatsoever.

[twobitshifter]

There actually is some evidence. I remembered this article but I’m no expert. https://www.smithsonianmag.com/science-nature/dna-search-fir...

[AlotOfReading]

The authors' speculation that this was due to both populations originating in east Asia eventually turned out to be true once further work was done on sequencing Tianyuan man [1]. It's not indicative of Pleistocene trans-pacific contacts.

[1] https://doi.org/10.1016/j.cub.2017.09.030