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[QUOTE]Originally posted by the lioness,: [QB] Razib Khan on Africa http://www.unz.com/gnxp/afro-asiatic-and-eurasian-backflow/ [b]Afro-Asiatic and Eurasian Backflow[/b] RAZIB KHAN • NOVEMBER 26, 2016 If you follow Y genealogy you know that the distribution of R1ba2 exhibits a peculiar pattern. R1b is the most common haplgroup in Western Eurasia, and shares a deep common ancestry with R1a. It seems to have risen to high frequencies in Europe only during the Bronze Age, though has been found in earlier periods. But within Africa R1b is found in very high concentrations around Lake Chad. This particular R1b lineage seems to have diverged from other Eurasian branches in the latter portion of the Pleistocene, so one possible consideration is that this was an instance of Eurasian backflow during the Ice Age. One reason I have been somewhat skeptical of this model is that the Sahara desert was much more extensive and arid during much of the Pleistocene than today. And during this period humans had less cultural technology to endure the rigors of the deep desert. Or, if they did, their population densities were likely much lower, which probably served as an impediment to gene flow. A new paper in The American Journal of Human Genetics sheds light on what might have been going on here.[b] Chad Genetic Diversity Reveals an African History Marked by Multiple Holocene Eurasian Migrations.[/b] The major findings are straightforward. First, much greater sampling of populations, and a better depth/density of marker coverage, allowed the researchers to detect low levels, on the order of ~1%, Eurasian admixture in some Central African groups. This admixture seems to date to the Holocene, ~5,000 to ~7,000 years before the present (they used LD based methods on the autosome). Interestingly, the R1b lineage common in Central Africa also seems to coalesce during this time. Finally, the admixture seems to be closest to Sardinians among extant populations. The Sardinian affinity of much of African Eurasian admixture may seem peculiar, but it makes more sense when one considers that Sardianians are probably the best modern proxies for the earliest Neolithic farmers from the Eastern Mediterranean. Modern Middle Eastern populations are very different from those which flourished in the prehistory between the rise of agriculture and complex civilizations because of admixture within Middle Eastern groups. The initial push into Africa by the agriculturalists dates to a period before we have a good understanding of the ethnographic balance. Very high frequencies of R1b in modern Central Africa groups may indicate drift. But another possibility is that the migration was male-mediated. This seems to have been the case in much of Eurasia, so it would not be surprising in this context. The status of these males was such that despite their diminishing genetic impact on overall ancestry, their Y chromosomes, and possibly their language, with varied forms of Afro-Asiatic, persisting down to the present. Finally, here’s the last paragraph of the discussion: [i] Our study has shown that human genetic diversity in Africa is still incompletely understood and that ancient admixture adds to its complexity. This work highlights the importance of exploring underrepresented populations, such as those from Chad, in genetic studies to improve our understanding of the demographic processes that shaped genetic variation in Africa and globally.[/i] http://www.razib.com/wordpress/?cat=579 December 1, 2012 [b]Africa’s hidden people hold the keys to the past[/b] I mentioned this in passing on my post on ASHG 2012, but it seems useful to make explicit. For the past few years there has been word of research pointing to connections between the Khoisan and the Cushitic people of Ethiopia. To a great extent in the paper which is forthcoming there is the likely answer to the question of who lived in East Africa before the Bantu, and before the most recent back-migration of West Eurasians. On one level I’m confused as to why this has to be something of a mystery, because the most recent genetic evidence suggests a admixture on the order of 2-3,000 years before the past.* If the admixture was so recent we should find many of the “first people,” no? As it is, we don’t. I think these groups, and perhaps the Sandawe, are the closest we’ll get. Publication is imminent at this point (of this, I was assured), so I’m going to just state the likely candidate population (or at least one of them): the Sanye, who speak a Cushitic language with possible Khoisan influences. There really isn’t that much information on these people, which is why when I first heard about the preliminary results a few years back and looked around for Khoisan-like populations in Kenya I wasn’t sure I’d hit upon the right group. But at ASHG I saw some STRUCTURE plots with the correct populations, and the Sanye were one of them. I would have liked to see something like TreeMix, but the STRUCTURE results were of a quality that I could accept that these populations were not being well modeled by the variation which dominated their data set. Though Cushitic in language the Sanye had far less of the West Eurasian element present among other Cushitic speaking populations of the Horn of Africa. Neither were their African ancestral components quite like that of the Nilotic or Bantu populations. The clustering algorithm was having a “hard time” making sense of them (it seemed to wanted to model them as linear combinations of more familiar groups, but was doing a bad job of it). Here is an interesting article on these groups: Little known tribe that census forgot. Like the Sandawe this is a population which seems to have been hunter-gatherers very recently, and to some extent still engage in this lifestyle. In this way I think they are fundamentally different from Indian tribal populations, who are often held up to be the “first people” of the subcontinent. More and more it seems that the tribes of India are less the descendants of the original inhabitants of the subcontinent, at least when compared to the typical Indian peasant, and more simply those segments of the Indian population which were marginalized and pushed into less productive territory. Over time they naturally diverged culturally because of their isolation, but the difference was not primal. In contrast, groups like the Sanye and Sandawe may have mixed to a great extent with their neighbors (and lost their language like the Pygmies), but evidence of full featured hunting & gathering lifestyles implies a sort of direct cultural continuity with the landscape of eastern Africa before the arrival of farmers and pastoralists from the west and north. * I understand some readers refuse to accept the likelihood of these results because of other lines of information. I am just relaying the results of the geneticists. I am not interested in re-litigating prior discussions on this. We’ll probably have a resolution soon enough. January 16, 2012 [b]The Fulani have an old “Berber” (?) element[/b] fter the second Henn et al. paper I did download the data. Unfortunately there are only 62,000 SNPs intersecting with the HGDP. This is somewhat marginal for fine-grained ADMIXTURE analyses, though sufficient for PCA from what I recall. That being said, the intersection with the HapMap data sets runs from ~190,000 SNPs, to the full 250,000 SNPs (this makes sense since the Henn et al. #2 data set has some HapMap populations in it). So I’ve been experimenting a fair amount in the past few days, and I thought I would post on one issue which was clear in the original paper, but which I have replicated. The Fulani (Fula) people of the western Sahel seem to have a relatively old West Eurasian component which has distinct affinities with the “Maghrebi” element discerned by Henn et al. In fact, the non-Sub-Saharan African ancestry of the Fulani is almost exclusively of this origin. To me this serves as a peculiar mirror of what you see in the Cushitic and Ethiopian Semitic peoples of the far east of the Sahel-Sudan latitudinal region. These populations also seem to be compounds of a Sub-Saharan Africa element with a West Eurasian one, but in their case the admixture is almost exclusively from a Southwest Eurasian (Arabian) component. Geographically these two symmetric admixture events make sense, but the exclusivity is still a bit surprising. Additionally, in both the case of the Fulani and the Ethiopian and Cushitic groups the admixture is widely distributed and even enough to imply that they are old events. I also assumed this because in some admixture runs a “pure” Fulani cluster partitions out, which is not unexpected for stabilized hybrid populations (all human populations are stabilized hybrids if you go back far enough). To give you a flavor of what I’m talking about here are some screen shots of a run which is currently going. It has 180,000 markers. I removed Tunisians and many African populations from the Henn et al. data set, and included in the Utah whites from the HapMap. The individual plots show the ancestral proportions for each Fulani in the data set: (see link for graphic) So what can we see here? First, let’s reiterate something: as in the case of the populations of the Horn of Africa the West Eurasian element in the Fulani is difficult to find in “pure” form in the populations from which it putatively derived. What does that imply? I think that that means that the Fulani have an origin in relatively recent historic time, on the order of 2,000, not 10,000, years. That is because I am skeptical that the Fulani would be able to maintain genetic distinctiveness for ~10,000 years from other populations around them. In contrast, the last 2,000 years have seen the rise of various cultural institutions, from trans-Saharan nomadism to Islam, which might slow down admixture sufficiently to maintain the differences between the Fulani and their neighbors. It also implies to me that the non-Maghrebi “Near Eastern” element which Henn et al. discerned is relatively a recent phenomenon in northwest Africa, else the Fulani should also carry it. How recent? Probably from Classical Antiquity down to the Muslim period. Observe that many North Africa groups have a red “European” element. This may be from Near Eastern populations, but I suspect that the fraction here is just too high to be explained by that. Also, you can see above that some groups in Morocco have nearly as much of this as Egyptians, but far less of the more genuine Near Eastern components. In all likelihood the West Eurasian component came to the Fulani via the Tuareg or a related or antecedent population. So if you typed the Tuareg you would probably get a better sense of the “pure” “Maghrebi” genetic profile. These genetic results also can serve as fodder to understanding the ethnogenesis of the landscape of the Sahel. In the map above it is interesting to observe that the Hausa speak an Afro-Asiatic language, even though their West Eurasian component is far lower than the Fulani, who speak Niger-Congo dialects. What gives? I suspect that the difference here is that the Hausa are a case of elite emulation of a cultural complex which was much more integrated and elaborated by the time it arrived on the West African scene. This explains how there could be language shift, while in the case of the Fulani there was none. Another hypothesis is that Afro-Asiatic derives from Sub-Saharan Africa itself, and the Chadic (Hausa) group are basal to the phylogeny. I’ll let readers explore the implications of that. A final aspect, I put the quotations in the title because perhaps the Berber dialects spread via elite emulation, and the original Maghrebi ancestors of the Fulani spoke a different language, which has been lost? As they say, for every answer there bloom a thousand questions…. [/QB][/QUOTE]
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