Planet Earth

We are all...Sardinians?

Gene ExpressionBy Razib KhanMar 18, 2012 6:54 PM

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The title is tongue in cheek. But I have been noting with interest Dienekes' trial runs with TreeMix. With it he has discovered a very peculiar admixture event, at least as determined by the software. The results are below, with my clarifying labels:

Basically the software seems to be implying that there has been gene flow into the Yoruba of West Africa from from populations related to the Basque & Sardinians. The most plausible explanation for this would be that this migration event was ancient, so that later admixtures of European populations are not reflected. Whether you believe that the Basque/Sardinians are Neolithic or pre-Neolithic (i.e., that they derive from Holocene settlers, or derive from Paleolithic European substrate), it is probably true that they have a relatively long period of residence in Western Europe. First, do not take these results at face value. Results generated by abstract methods sometimes make no sense. Often they're only as good as their assumptions, and the common sense of the humans utilizing the methods. As a classic case in point Allan Wilson, whose group later propounded the mitochondrial Eve theory, originally reported to some journalists in the early 1980s that modern humans may have derived from Australia! There was a reason for this, and that had to do with some problems in the phylogenetic methods they were using (or at least the way they were using it). Later on common sense, and all of archaeology, realigned with the phylogenetics when the research group went over their methods. Until lots of people use TreeMix and start to find similar results I would be very cautious about taking any given counter-intuitive result as plausible. With all that being said, I think that these results may point to a broader truth which is only starting to shake out: the prehistory of Africa has been much more complex than we had assumed, and the 'Out of Africa' model has blinded us to this. One finding which seems reasonably robust is that there is a large difference between the hunter-gatherer populations of the continent, and other Sub-Saharan Africans. Depending on the method you use the most reasonable clade may even be African hunter-gatherhers vs. everyone else (including agriculturalist Africans). There has been massive genetic-demographic change in Southeast Asia and South Asia, so why would Africa be any different? In fact, we know it's not any different, the Bantu expansion has totally reshaped Africa over the past 3,000 years. And why should we stop at that? Is it too implausible that there was back migration from Eurasia during the Neolithic Subpluvial, during which there was a "Green Sahara"? Actually, I would bet that the back migration was a little more ancient, but that is neither here nor there. If the past is as complex as I think it might be then the idea that 'We are all Africans' may still be true, but it may also be trivial....

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