Wednesday, March 26, 2014

proto-Native American admixture into Mal'ta Boy, a more parsimonious and yet "contrarian" model

Although it has become universal to speak of the Mal'ta find's admixture into Native Americans, there is actually an alternative, more parsimonious model that explains the data equally well, and that model is proto-Native American/paleo-Siberian admixture into Mal'ta boy. It's important to understand that no Mal'ta Boy genes have been found in Native Americans. Rather, Lazaridis et al. inferred Mal'ta admixture into NA based on the differing genetic distances of various Eurasian populations to Mal'ta Boy. Below are the f4 statistical phenomenon that led Lazaridis to reach their conclusions:
1. Mal'ta is roughly equidistant  in f4 stats to Oceanians and East Asians while closer to Native Americans
2. Mesolithic Europeans and Mal'ta are roughly equidistant to East Asians while Malt'a is much  closer to Native Americans than Europeans are.

Model A, Mal'ta admixture into Native Americans, would explain the above phenomenon. However, it requires 2 hypothetical populations: Ancestral North Eurasian and Basal Eurasian.
Model B, proto-Native American/paleo-Siberian admixture into Mal'ta, requires no hypothetical populations.

Model A
One way to explain these curious mathematical artifacts is through a model of Mal'ta admixture into Native Americans. Because Native Americans are admixed with Mal'ta, they are closer to Mal'ta. Because East Asians are unadmixed wit Mal'ta, they are as distant to Mal'ta as faraway Oceanians are to Mal'ta. Because Native are admixed with Mal'ta, they are much closer to Mal'ta than they are to Europeans, whereas because East Asians have neither Mal'ta nor European admixture, both Euroepans and Mal'ta are equidistant to East Asians.
A complication to this model is that it requires the positing of 2 hypothetical populations, Ancestral North Eurasian and Basal Eurasian, neither of which can be matched into archaeological reality.. Mal'ta as a pure population would require it to be a separate Ancestral North Eurasian because it is very distinct genetically. Because Eastern Eurasians, Native Americans, Oceanians are all closer to Mesolithic Europeans than they are to Near Easterners. This would require pre-Neolithic Europeans to form a macro-clad with other Eurasians to the exclusion of Near Eastern Basal Eurasians.

Model B
The 2nd model is actually more parsimonious because it explains the interlocking genetic distances of various Eurasian populations without a need for hypothetical populations. Because Native Americans are actually quite distinct from East Asians and show up on a multi-dimensional plot in its distinct "corner", any Native American admixture into Mal'ta would not make them noticeably closer to East Asians, thus explaining the perplexities 1 and 2 above.

The Mal'ta --> Native American model creates serious archaeological and epigenetic/physical anthropology conundrums:
1. Both Ancestral North Eurasian and Basal Eurasian that Lazaridis et al. proposes are hard to match up with any archaeology. Mal'ta-Buret Culture arrives in Siberia 20,000 years after the initial Upper Paleolithic there, and Mal'ta-Buret has long been noted as an intrusive element in Siberia with a mixture of European Gravettian cultural artifacts and Central Asian lithic characteristics.
2. The whopping ~40% admixture into Karitiana would also not explain why Native Americans are on the extreme end of East Eurasian epigenetic traits (i.e. EDAR, Sinodonty). While on average Native Americans and modern East Asians are rather distinct, physical anthropologists do not find Native American skull craniomorphology and craniometrics to be a watered down version of East Asians, and in fact Plains Indian and Mongolian defleshed skulls resemble each other more than both to Chinese, Japanese, etc.


Other problems with the Mal'ta find:

Their closest approximant are the Mari people of Uralic Russia. In the clustering analysis (at K10), the Mari are about 30% Siberian, which peaks at the Ngansan around 100%. Mari mtDNA is 13.2 East Eurasian.
source: Diversity of Mitochondrial DNA Haplogroups in Ethnic Populations of the Volga–Ural Region

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