
This paper in PNAS, Gene flow from North Africa contributes to differential human genetic diversity in southern Europe, is the best survey I know. It establishes a few points. For example, the Basque differ from people from other regions of Spain in that they lack much evidence of North African admixture. The historical and social separation of the Basque country during the Moorish period, and also after the Reconquista, is a pretty good rationale for why this might be. Second, the paper establishes some regional variation in the admixture. There’s more in Andalusia. Roughly, it seems that areas closer to North Africa, but probably more significantly under Muslim rule longer, have more admixture from the Maghreb. Third, a lot of it is too recent to be Roman. Looking at segment length the authors estimate a lower bound of ~300 years. After reading the post from Saturday you should understand why this statistic needs to be handled with caution. Additionally, it is important to note that the gene-sharing between Spaniards and North Africans occurs in cases where the North African population of interest has no European ancestry at all. That is strongly indicative of gene flow from North Africa to Europe, rather than bidirectional dynamics. Finally, it looks to be that pretty much all the very low level Sub-Saharan admixture you can find in Spain is attributable to the Moorish period, because the Berbers and Arabs who arrived had that element in their ancestry due to the ubiquity of the trans-Saharan slave trade.


Cook does grant that a substantial number of Muslims in China assimilated to a Han identity. This is well attested for elite lineages of Muslims and Jews (from Kaifeng), whose entrance into the mandarin class of scholar-bureaucrats almost always presaged total assimilation. But it is probably at least as true for the vast majority of non-elite Hui, many of whom also shifted toward the Han identity. In the 20th century it was a truism among the Hui, reported without much skepticism, that Han can become Hui (through conversion), but the converse is not true. The problem with this is that the social norms and mores as such that movement from Hui to Han is never going to be widely documented, while a shift in the other direction will be. As it happens, there is now ethnographic evidence from southern China and Taiwan of whole communities which shifted from Hui identity to a Han one, with their Muslim origins being preserved in oral memory, as well as the persistence of customs such as not offering pork on ancestral graves in deference to the religion of these forebears. Over the past few centuries Muslim communities in China proper have become reintegrated into the world-wide Ummah, and undergone several waves of reform which have resulted in conformity with world normative Islam. But before this it seems likely that there was a continuous flow of Hui into the Han population through assimilation, in particular because there are many documented beliefs of Hui in the 18th century which seem to suggest a convergence with Daoism and Pure Land Buddhism.
All this is not to say that Cook’s thesis, and the public perception, does not have an element of truth to it. It is simply that the reality is a little more complex and less supportive after you scratch below the surface.
Genetic addendum: I have my own data sets, and decided to double check the results above. Including in these data the 1000 Genomes IBS (Spain) samples. You can see from the PCA and TreeMix (all of them exhibited the same topology) that something is going on with non-Basque Spaniards. The Italian position is explained by the fact that these are southern Italian samples, and those tend to exhibit affinities to Eastern Mediterranean groups. Please note that I removed all markers with missing calls and outliers as well. There were 130,000 SNPs in the final data.




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