Update 20/02/2013: Ancient Amerindian-like admixture in Europe - something doesn't add up
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Earlier this year, Patterson et al. found that Europeans were a mixed population with significant prehistoric ancestry from North Asia. The theory put forward was that we were a two-way mix between Neolithic farmers who resembled genetically modern Sardinians, possibly from the Near East, and native European Mesolithic hunter-gatherers, who's best modern proxy seemed to be South American Indians. However, a pre-print at arXiv, courtesy of some of the same authors who wrote the Patterson et al. paper, proposes that Europeans might be a mix of three ancient groups: Neolithic farmers, Mesolithic European hunter-gatherers, and/or Mesolithic North or Central Asians. In fact, this model is very similar to the one I entertained in my blog entry about the Patterson et al. paper, in which I said that Mesolithic European hunter-gatherers carried a North Eurasian component, rather than being entirely of North Eurasian stock (see here). This makes sense in the light of ancient mtDNA results, which show Mesolithic Europeans carrying mostly West Eurasian-specific U4 and U5, but with some samples from Mesolithic and Neolithic Europe featuring a minority of Siberian-speific markers such as C.
Using MixMapper, we added each of the European populations to the unadmixed tree via admixtures (Figure 4; Table 1). For all eight groups in the HGDP data set, the best fit was as a mixture of a population related to the common ancestor of Karitiana and Suru´ı (in varying proportions of about 20-40%, with Sardinian and Basque among the lowest and Russian the highest) with a population related to the common ancestor of all unadmixed non-African populations on the tree. All eight European populations were fit independently, but notably, their ancestors were found to branch from the scaffold tree at very similar points, suggesting a similar broad-scale history.Lipson et al., Efficient moment-based inference of admixture parameters and sources of gene flow, arXiv:1212.2555v1 [q-bio.PE]
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Our interpretation is that most if not all modern Europeans are descended from at least one large-scale ancient admixture event involving, in some combination, at least one population of Mesolithic European hunter-gatherers; Neolithic farmers, originally from the Near East; and/or other migrants from northern or Central Asia. Either the first or second of these could be related to the “ancient western Eurasian” branch in Figure 4, and either the first or third could be related to the “ancient northern Eurasian” branch. Present-day Europeans differ in the amount of drift they have experienced since the admixture and in the proportions of the ancestry components they have inherited, but their overall profiles are similar.
I not Asian. Shit! Why I talk like this? Noooooo.
ReplyDeleteBased on Table 1, the "European" populations surveyed have the following midpoints for estimated alpha, the proportion of ancestry from the “ancient northern Eurasian” side -
ReplyDeleteAdygei - 0.357, Basque - 0.272, French - 0.285, Italian - 0.312, Orcadian - 0.253, Russian - 0.382, Sardinian - 0.25, Tuscan - 0.305
Based on Table 3 and the Sardinian proportion, Middle Eastern populations should present with the following proportions of "ancient northern Eurasian"-
Druze - 0.24, Palestinian - 0.23, Bedouin - 0.22, Mozabite - 0.18
^ OK, thanks. I think there's probably a bit more work to be done in getting those figures right.
ReplyDelete^
ReplyDeleteYes, I'm sure that's true.
I mainly thought those were worth posting because I, for instance, read the text summary and assumed at first that it followed a pattern with Russians having a high at 40%, Sardinians at 20% and, also inferred or assumed Middle Eastern populations would hit 0%. Following a smooth North East Europe->Western Europe->South East Europe->Middle East pattern clinal.
But, although that would be in the right direction, that's not exactly what it seems they have found...
.... which (with the caveat that relatively few populations have been covered)looks more like a relatively constant level in West Eurasian populations with deviations mainly explained by mixture with African populations (for Middle Eastern populations) and (although not explicit in the paper) by recent admixture with North Eurasian populations (e.g. in Adygei and Russians, who have an elavated proportion of North Eurasian and ancestry both have signals of relatively recent admixture per Patterson 2012).
Of course, if this is the case, then we are back in the situation of trying explain closer Southern European affinities to Africans relative to Northwest Europeans, and the MixMapper model does not seem to indicate admixture from Africa to Southern Europe...