Razib Khan One-stop-shopping for all of my content

April 9, 2011

The Sandawe: after the demographic flood

Filed under: African Genetics,African Genomics,Genetics,Genomics,History,Sandawe — Razib Khan @ 9:21 pm

Over the past few days I’ve been trying to read a bit on the Sandawe. Most of the stuff I’ve been able to find is in the domain of linguistics, and is basically unintelligible to me in any substantive manner. The crux of the curiosity here is that the Sandawe, like their Hadza neighbors, have clicks in their language, and so have been classified with the Khoisan. Here’s some background:

The most promising candidate as a relative of Sandawe are the Khoe languages of Botswana and Namibia. Most of the putative cognates Greenberg (1976) gives as evidence for Sandawe being a Khoesan language in fact tie Sandawe to Khoe. Recently Gueldemann and Elderkin have strengthened that connection, with several dozen likely cognates, while casting doubts on other Khoisan connections. Although there are not enough similarities to reconstruct a Proto-Khoe-Sandawe language, there are enough to suggest that the connection is real.

I can’t speak to the validity of this at all, obviously. Some scholars do argue that the clicks in the Sandawe language were only acquired through interaction with peoples such as the Hadza, making an analogy to Xhosa, a Bantu language which has been strongly influenced by Khoi dialects. ...

April 6, 2011

Africa in 12 ADMIXTURE chunks

Some have asked what the point is in poking around African population structure when Tishkoff et al. and Henn et al. have done such a good job in terms of coverage. First, it is nice to run your own analyses so you can slice & dice to your preference, and not rely on the constrained menu provided by others. There’s value in home cooking; you can flavor to your taste. Second, you never know what data people might leave on your doorstep. I’ve received the genotypes of three Somalis. Nothing too surprising, a touch more Cushitic than the Ethiopians in Behar et al., but interesting nonetheless.

Also, you can see how ADMIXTURE tends to come to weird conclusions in certain circumstances. Below is a K = 12 run ~50,000 SNPs. I’ve included in a few Behar et al. and HGDP populations to the Henn et al. set, as well as pruned a lot of the African groups which seem redundant in terms of information. I’ve added a few geographically informative labels as well.

Observe below that there is a Fulani cluster. I think this is pretty much an artifact. At K = 7 the Fulani have a majority component ...

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