Doubts about the "Tanzania_Zanzibar_First Millennium" aDNA sample

Ygorcs

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I decided to post this doubt of mine here so that someone might perhaps help clarify what's happening with the average population DNA sample named TZA_Zanzibar_FirstMillennium in Global25 datasheets. I have googled to try to find the paper that that sample comes from, but couldn't find it. The issue is that, running the sample into nMonte software to model its ancestry, it's clear that it's just too much of an outlier to be believed: the sample is closest to ancient Iberian samples and, among modern populations, also to Iberians. Okay, I wouldn't be totally surprised by a Portuguese trader/sailor being buried in Zanzibar in the 16th or 17th century (though I still think that would be a real find, as they must've been a tiny minority of the total population), but first millennium? Does anyone have any information about that DNA sample, the study that analyzed and released it, the dating and archaeological circumstances? For now I'll just assume that the labeling was totally wrong and it in fact dates to the last centuries.
 
Zanzibar traded heavily with the Arabs and the Indian ocean nations in the first millennium, particularly from the 8th through 10 century.

The Umayyad conquest of Hispania ran from 711 to 788, and put pretty much the whole population of Iberia in the Arab sphere from then on.

I see nothing strange in individuals of Iberian heritage showing up in any place the Muslims traded towards the end of the first millennium.
 
Nothing to do with R1b-L51, Cyrus. The sample is autosomally almost identical to modern Portuguese and Spanish people and shares a very similar combination of genetic admixtures with them, also having low genetic distance from them. All of those observations are about genome-wide connections, not simply a matter of having a certain Y-DNA haplogroup formed more than 5000 years ago, which additionally has nothing specifically Iberian about it.
 
Arab traders were in Zanzibar 800 AD, and with a rapidly increasing presence. The Arab sphere at the time included millions of people of a European genetic heritage. The inclusion of Iberia alone may well have added a million or more, Iberia was always a fertile part of the Roman empire, and the Visigoths were one of the more successful dark ages successor nations. Then you have the Vandal descendants in North Africa, as well as rather an enormous slave trade with raiding of European shores. You may even have the occasional descendant of people who moved to the Levant and Mesopotamia during Roman times, and went a few centuries without mixing with the locals. As well as people coming in from Constantinople.

The rapid expansion of the Rashidun and Umayyad caliphates in the seventh and eight century must have resulted in a population that at the time was extremely heterogeneous, genetically. They had not had the time to homogenize.

And that the body in question was of European genetic heritage does not actually mean that he was European. One of the effects of large empires like this is that it eases trade, and often wipe out a lot of bandits. Movement of individuals increases a lot. The persons parents or even grandparents could have moved to Yemen, Medina, or Cairo for example from some other Muslim controlled area.
 

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