Ancient west Eurasian ancestry in southern and eastern Africa
Joseph K. Pickrell, Nick Patterson, Po-Ru Loh, Mark Lipson, Bonnie Berger, Mark Stoneking, Brigitte Pakendorf, David Reich
(Submitted on 30 Jul 2013)
The history of southern Africa involved interactions between indigenous hunter-gatherers and a range of populations that moved into the region. Here we use genome-wide genetic data to show that there are at least two admixture events in the history of Khoisan populations (southern African hunter-gatherers and pastoralists who speak non-Bantu languages with click consonants). One involved populations related to Niger-Congo-speaking African populations, and the other introduced ancestry most closely related to west Eurasian (European or Middle Eastern) populations. We date this latter admixture event to approximately 900-1,800 years ago, and show that it had the largest demographic impact in Khoisan populations that speak Khoe-Kwadi languages. A similar signal of west Eurasian ancestry is present throughout eastern Africa. In particular, we also find evidence for two admixture events in the history of Kenyan, Tanzanian, and Ethiopian populations, the earlier of which involved populations related to west Eurasians and which we date to approximately 2,700 – 3,300 years ago. We reconstruct the allele frequencies of the putative west Eurasian population in eastern Africa, and show that this population is a good proxy for the west Eurasian ancestry in southern Africa. The most parsimonious explanation for these findings is that west Eurasian ancestry entered southern Africa indirectly through eastern Africa.
Haldane's Sieve 
http://blogs.discovermagazine.com/gnxp/2013/07/reconstructing-genetic-ripples-in-time-and-space#.Ufne1n6EW2R
Commentary by John Hawks: http://johnhawks.net/weblog/reviews/genomics/modern/african-gene-flow-pickrell-2013.html and news article by Erika Check Hayden: http://www.nature.com/news/african-genes-tracked-back-1.13607
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How do you think the putative west asian ancestry contributing population ties in to putative ADMIXTURE clusters found in the haber et al 2013 paper in terms of the ‘southern levantine’ genetic component (which is the only one found in the ethiopian samples)? And when do you think the genetic landscape of the middle east changed into what it is now vs before?
Link to Haber’s paper
http://www.plosgenetics.org/article/info%3Adoi%2F10.1371%2Fjournal.pgen.1003316
(see figure 4 in the paper). Also in regards to the last question I had, I was meaning to refer to how the majority of west asians and arabians carry elements of the ‘blue cluster’.
Thanks for pointing me to the Haber paper; I’d not noticed the east African samples there. I have a bit of evidence now that the west Eurasian ancestry in east Africa is most closely related to the Bedouins, which is consistent with that figure (though based on that the figure, I’ll also look at the Saudis).
As to the timing of demographic events in the Middle East, I don’t think I’ve seen any genetic evidence pointing to any particular time, though I could be missing something.
Ah ok, that makes much more sense. And I agree I couldn’t point to anything either, other than perhaps the spread of the afroasiatic language family from a source population which derived ancestry with levantine bedouins (considering the distribution of the green cluster)? Though it must have been an isolated population in order to not share the more common ‘blue cluster’ found in the mediteranean.