There are two new papers out on the early colonization of the Americas, one in Science and one in Nature. The Science paper claims that all Amerindians stem from a single Siberian population that moved into Beringia about 23,000 years ago and entered America about 15,000 years ago, splitting into northern and southern branches about 13,000 years ago. They also found a touch of Australo-Melanesian ancestry among some, not all, living Amerindians – they saw it in Aleuts and the Surui ( Amazonian Indians). They concluded that this ancestry must have arrived well after the initial colonization of the New World: “The widely scattered and differential affinity of Native Americans to the Australo-Melanesians, ranging from a strong signal in the Surui to much weaker signal in northern Amerindians such as Ojibwa, points to this gene flow occurring after the initial peopling by Native American ancestors.” In much the same way, the fact that you see widely different amount of Bushman admixture in Bantu groups in southern Africa ( a lot in the Xhosa, almost none in some other groups) suggests that the Bushmen arrived after the Bantu, except that it doesn’t of course.
The Nature paper concentrates on the Australo-Melanesian story: they see it mainly in the Amazon Basin, 1-2%. The closest extant population is the Onge, pygmies of the Andaman Islands, but you see this anomalous relatedness in the Papuans, Australian Aborigines, Mamanwa (Philippine Negritos), and at lower levels in a number of groups in South Asia. In many Amerindian groups this component is much weaker or nonexistent.
The authors of the Nature paper believe that this admixture most likely happened before the settlement of the Americas, but they aren’t sure: the linkage disequilibrium says some time between 40,000 and 4,000 years ago, probably after the Ancient North Eurasians mixed into the Amerindians. They talk about population Y, a separate movement into the Americas by a population that had probably already acquired this Australo-Melanesian component.
The background fact is that the earliest skeletons, especially in Brazil, look like Australo-Melanesians. Long skulls. If population Y were almost entirely standard Amerindian, with only a smidgen of Australo-Melanesian ancestry, they would have looked like Amerindians. On the other hand, if the original settlers of the Americas were mostly or entirely Australo-Melanesian (or more exactly something vaguely related to those existing populations) they would have those long, narrow skulls. This is the Paleoamerican model – and if true, it means that an Onge-like population arrived first, and that the incoming Amerinds almost completely wiped out them out later, with here and there a bit of admixture.
As I understand the law, this would mean that we have to build little casinos inside the existing casinos. For some small establishments, this might mean designating the proceeds of a single slot machine to various Amazonian tribes, or possibly to the Onge as next of kin.
* It’s complicated.