There’s a new paper out on the people of the Americas, by Pontus Skoglund and David Reich. The main picture is solidifying:
The main Amerindian migration consists of a population that is approximately 40% ancient Siberian and 60% Han-like. Calculations that assumed a simple split between the ancestors of the Han and Amerindians are wrong and probably placed too far back (~23,000 years BP). They don’t mention it, but the uniparental lineages suggest that ANE guys ran off with some sobbin’ proto-Han women, much like the formation story for the Indo-Europeans.
There was some substructure: the two main streams are the Amerindians of South and Central America and northern Amerindians like Cree and Algonquins. Interestingly, the only Clovis skeleton we have is genetically closer to the southerners.
The paleo-Eskimos (Dorset culture) come from a later, separate migration (~4500 years ago), similar to Koryak and Chukchi, but were completely replaced by the Thule culture (current Eskimos) ~1000 years ago.
The Na-Dene (Navajo for example) also came late: they might be from the same stream that led to the Dorset, but they might stem from another migration. Better samples from more populations should soon resolve this. Since Na-Dene languages can be related to Ket using standard methods, it can’t have been all that long ago – more like 4 or 5 thousand, rather than 8 or 9.
According to this paper, the Andamanese-like admixure is found only east of the Andes in South America, apparently concentrated in the Tupi language family. Not in the Eskimos, not in central America, not in Canada, not in the one Clovis skeleton we have, which has affinities to the Central/South America branch. Not in Tierra del Fuego, not in Baja California.
I think this strong pattern significantly increases the probability of the scenario in which a vaguely Andamanese-like population gets to the Americas first, maybe 18k years ago, came by sea and settled Brazil, which was decent hunter-gatherer territory (savannahs and open woodland), not ice/polar desert/taiga like North America. Then was replaced, with a little admixture, by a classic Amerindian population. I would guess that the authors think so too: they’re treating this scenario with more respect than in the earlier paper. They mention the odd-looking early skeletons in Brazil.
We need ancient DNA to seal the deal, but that may come.
Why didn’t these Andamanese-like guys drive extinctions? Cause the megafaunal extinctions are a good deal later. I’m guessing that they were originally fishermen and beachcombers, not hard-case hunters of big mammals like the Amerindians in Beringia. Modern humans didn’t cause instant extinctions in Africa (only some things) but the animals there had a long time to adapt to people, while sleeping sickness eventually created people-free zones. . South America wasn’t like that – why didn’t these Andamanese wipe out the big game? Well, from what we know they weren’t very good at dealing with Amerindians – and related populations in Southeast Asia, the Philippines, and Indonesia also lost out to Han-like invaders.
Yet even the Australian aborigines seemed to have wiped out the Australian megafauna pretty rapidly… In our scenario, why didn’t the pseudo-Andamanese?
Something limited their ecological dominance.