Characterizing the history of sub-Saharan African gene flow into southern Europe.
P. Moorjani1, N. Patterson2, J. Hirschhorn1,3, D. Reich1,2. 1) Department of Genetics, Harvard Medical School, Boston, MA; 2) Broad Institute, Cambridge, MA; 3) Divisions of Endocrinology and Genetics and Program in Genomics, Children’s Hospital, Boston, MA.
Recent analyses of whole-genomeSNP data sets have suggested a history of sub-Saharan African ancestral contribution into southern Europe but not in northern Europe, consistent with previous analyses based on the Ychromosome and mitochondrial DNA. However, there has been no characterization of the proportion of African admixture in southern Europe, or of its date. Here we analyze data from ~450,000 autosomal SNPs in the Population Reference Sample, ~650,000 SNPs from the Human Genome Diversity Panel, and ~1.5 million SNPs from the HapMap Phase 3 Project, and studied patterns of correlation in allele frequencies across populations to confirm the evidence of African ancestry in many southern European populations but not in northern Europeans. Using methods that can infer admixture proportions in the absence of accurate ancestral populations, we estimated that the proportion of sub-Saharan African ancestry in Spain is 2.4 +/- 0.3%, in Tuscany 1.5 +/- 0.3%, and in Greece 1.9 +/- 0.7% (1 standard error). We also studied the decay of admixture linkage disequilibrium with genetic distance, which provided a preliminary estimate of the date of African gene flow into Spain of roughly 60 generations ago, or about 1,700 years ago assuming 28 years per generation. This date is consistent with the historically known movement of individuals of North African ancestry into Spain, although it is possible that this estimate also reflects a wider range of mixture times.
An estimate of sub-Saharan autosomal admixture in southern Europe
Polak reports that ASHG 2009 abstracts are now up. I don't know how accurate these estimates are, but the finding that the proportion of sub-Saharan ancestry is highest in Iberia is consistent with the mtDNA evidence.
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"...a preliminary estimate of the date of African gene flow into Spain of roughly 60 generations ago, or about 1,700 years ago assuming 28 years per generation. This date is consistent with the historically known movement of individuals of North African ancestry into Spain, although it is possible that this estimate also reflects a wider range of mixture times."
I remember reading (can't remember where exactly) that there was a small population of Negro slaves (~5%) living in Portugal when the slave trade was active just a few hundred years ago, and that this population was gradually absorbed into the Portuguese population.
It wouldn't be too surprising if something similar occurred in Spain.
Wonder why there is SSA admixture in central Italy and Greece.
(Spain, as well as Sicily, I could understand- migration of North Africans with partial sub-Saharan ancestry.)
Perhaps the same applies to Tuscany, as it was home to the Etruscans, who were trading partners and allies of Carthage, and they may have obtained slaves from North Africa.
Greece is harder to explain. There were a few Nubian slaves (called "Aithiopians") in ancient Greece (mostly obtained through Egypt), but the vast majority of Greek slaves were Caucasians from southeastern Europe and Asia Minor.
Before people go all "True Romance" here, I will remind you that one can occasionally find traces of sub-Saharan ancestry in parts of Northern Europe- there was the "White" Yorkshire family with the West African yDNA haplogroup A1 (they may be descended from black sailors who settled in Britain during the slave trade era.)
Are Berbers considered sub-Saharan African in this study?
Choppy,
Out of all European countries, Portugal has the highest level of sub-Saharan mtDNA (with Spain coming a distant second). Absorption of African slaves within the past 500 years probably plays a role, along with the Moorish occupation and Mesolthic/Neolithic genetic exchange with North Africa.
patrick,
No need to speculate or go back nearly that far to find African slaves in Tuscany.
As well, the Ottomans brought African slaves to Greece, though I would guess most of the African component in Greeks diffused into Greece via the Middle East.
"there was the "White" Yorkshire family with the West African yDNA haplogroup A1 (they may be descended from black sailors who settled in Britain during the slave trade era.)"
Note that the widely publicized paternal lineage you refer to is the most unusual out of thousands tested in Britain. Nor was there ever any evidence that it came to Britain with an "African sailor" (it's too old, for one thing). It most likely diffused northward via North AFrica long ago.
Justin,
No. Berbers are predoinantly Caucasoid, with significant sub-Saharan admixture.
You are right that the haplogroup A1 is rare (not only in England but also in West Africa). And you are correct that it may be much older than the slave trade era.
Maybe it arrived in Roman times. Several skeletons found in excavations of Roman York show Negroid characteristics, and some of the North African soldiers stationed along Hadrian's Wall may have had sub-Saharan paternal ancestry.
Obviously there weren't very many of these Africans(only a tiny percentage of the population) and it is unlikely that any trace of their presence could be found through autosomal studies (the subject of this post).
Maybe it arrived in Roman times. Several skeletons found in excavations of Roman York show Negroid characteristics, and some of the North African soldiers stationed along Hadrian's Wall may have had sub-Saharan paternal ancestry.
That is possible, since we have archaeological evidence which indicates heavy Afro-Asiatic influence in the late Roman Empire (in the Senate and Royal family and in Roman commerce). Rome in those times was also colonized by immigrant populations from areas like Syria and North Africa. So a bit of black African and Semitic heritage may have crept into the populations of western Europe this way. Though obviously it is a rare component.
The idea that Rome was colonized by northafricans and siryans,it has been largely dismounted.
The few imperial families with northafrican or syrian roots were for the most with almost a parent of italic origin,see Severus and he was clearly white.Not to forget that many of the syrian and northafrican people in Rome were traders not citizens,and that celts and germans too were largely a portion of Italy\Rome too.Slaves reached maximum 17 years old and as scholars say,hardly they reached the number of slaves in Victorian England.
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