Comments on the new Horn African and north Sudanese samples

Well, as you can see here, we have 13 new samples from southern Somalia, 10 from Ethiopia of -West-Central Oromo origins and about 17 Sudanese-Arab+Nubian samples from northern Sudan.

Some interesting things to note would be:

• The Somalis seem rather uniform in terms of their "African" & "West Eurasian" ancestry levels once you set aside the 3 outliers who look to have 30-50% West-Central African-related admixture of probably recent origins from Somali Bantus. [note] This is interesting because these same ~10 remaining Somalis display an odd substructure in the PCA where 3 samples, alongside at least two Oromos, pull quite northwards as though they're somehow slightly distinct from the other Horn Africans present in the PCA, even though all of the Somalis, except for those three outliers, seem more or less the same in regards to their admixture levels.

• The West-Central Oromos seem to be about as African & West Eurasian as the Somalis and, if I recall correctly, these types of Oromos tend to vary between being 40-50% West Eurasian from what I remember so the Somalis in question look to be relatively standard in terms of admixture levels for pulling about as eastwards toward West Eurasians as these Oromos. Some of these Oromos are more West Eurasian-shifted than the Somali samples which would make sense as well.

• The Sudanese Arabs and Nubians seem mostly more West Eurasian-shifted than the Somali and Oromo samples which, I suppose, could mean most of them are at Habesha~Agaw levels of African and West Eurasian ancestry while some, or even a decent number, possibly also surpass those admixture levels. They also definitely display signs of notable heterogeneity in terms of admixture levels which correlates well with prior data owed to Dobon et al.

One thing the way some of those Somalis cluster reminds me of is this, actually:

That PCA above, as discussed here, basically shows us that some of Lazaridis et al. 2013-2014's Somalis from Garissa seem slightly "Ethiopian-shifted" in a manner that might imply admixture from people like Borana Oromos, they're also very slightly less West Eurasian (on average) than the Somalis we so far have from Ethiopia and Somalia.

Now, this new study's Somali samples, originally from southern Somalia, are classified as "Sedentarian" which looks to impart that they're sedentary farmers rather than semi-nomadic pastoralists. Perhaps they're of the Rahanweyn clan (though they don't have to be) which has long had sedentary farmers within its clan-structure in the south? Some might notice that I once entertained the notion that some Rahanweyn clan members might have notable Ari-like admixture the way various Ethiopian populations do (see here). [note]

Well, perhaps the reason the majority of these Somalis are clustering so close to the West-Central Oromos is because they carry admixture from Oromo-related/like people and the ~3 who don't cluster that way and pull very upwards actually lack such admixture? 

But then it doesn't explain why all of the samples seem to be roughly the same in terms of West Eurasian and African ancestry levels (they're basically homogeneous in this case). Also, why do at least two West-Central Oromos actually pull north as well? And why do these Somalis seem so close to West-Central Oromos in terms of admixture levels which implies all of them have relatively typical Somali admixture levels? [note]

These issues don't make much sense if some of them are part Oromo (or even Borana Oromo-like) while others aren't.

So I suppose it may not be worth speculating too much with this study's PCA and ADMIXTURE run until we have these samples out in the open. There are also other odd things about these results like the Oromos showing tiny hints of West-Central African-related admixture when the non-outlier Somalis show none and that honestly doesn't make much sense to me so I'll have to just see these samples for myself when the time comes. 

I wouldn't be sure of too much until we can run these samples through other analyses but these are my quick two cents for now. 

References:

1. Extensive Admixture and Selective Pressure Across the Sahel Belt, Triska et al.