Sub-saharan Dna Admixture In Europe

Sub-Saharan DNA is scattered throughout the European population. Not every nation has been studied yet, but enough studies have been done that a picture is starting to emerge. The percentage of sub-Saharan DNA in Europe today ranges from a few percent (in southern Portugal) to nil (in Scandinavia). It decreases as you go northwards from the Mediterranean. It apparently decreases as you go eastwards from the Atlantic. There are four main approaches to detecting continent-of-ancestry markers in DNA: mtDNA, Y DNA, neutral autosomal markers, and adaptive autosomal traits. Each approach has strengths and weaknesses in distinguishing ancient sub-Saharan markers (from our species's common origin) from more recent ones. Some approaches are more quantifiable than others.

Between 1500 and 1900, about four million African slaves were transported to island plantations in the Indian Ocean, about eight million were transported north across the Sahara to the Mediterranean coast, about eleven million were taken to Latin America and about half a million were taken to North America.Pier M. Larson, Reconsidering Trauma, Identity, and the African Diaspora: Enslavement and Historical Memory in Nineteenth-Century Highland Madagascar , ''William and Mary Quarterly'' 56, no. 2 (1999): 335-62. The descendants of the four million taken to Indian Ocean plantations self-identify today with their various nationalities, rather than with Africa, but their appearance reveals their ancestry. The eleven million taken to Latin America genetically assimilated into the colonial populations, leaving unimodal DNA admixture scatter diagrams. Whether any given Latin American looks more or less European, African, or Native American depends upon each person's individual admixture within his nation's colonial demographic continent-of-ancestry ratios. Latin American populations as a whole are thoroughly mixed. The half-million taken to North America formed an endogamous (African American) community that is unique in having remained genetically distinct from the surrounding society for four centuries. Of the eight million taken to the Mediterranean coast, about 200,000 were sold into Europe.Hugh Thomas, ''The Slave Trade: The Story of the Atlantic Slave Trade: 1440-1870'' (New York: Simon and Schuster, 1997), 804. These seem to have vanished without a trace. And yet, the traces are there, in their DNA.

FOUR APPROACHES TO DETECTING CONTINENT-OF-ANCESTRY MARKERS IN DNA

For the complete text of several dozen studies measuring sub-Saharan admixture throughout Europe including England, Belgium, Finland, and the Balkans as well as along the Mediterranean, see Various Admixture Studies . Each study is summarized in the index and identified as to which markers it used (mtDNA, Y, neutral autosomal, adaptive autosomal).
In short, although African DNA is present everywhere in Europe, it is too thinly scattered, even along the Mediterranean coast, to affect physical features.

There are four main approaches to detecting continent-of-ancestry markers in DNA: mtDNA, Y DNA, neutral autosomal markers, and adaptive autosomal traits. Each approach has strengths and weaknesses in distinguishing ancient sub-Saharan markers (from our species's common origin) from more recent ones. Some approaches are more quantifiable than others.

Mitochondrial DNA (mtDNA) and Y-chromosome DNA trace individual lineages

Mitochondrial DNA (mtDNA) and Y-chromosome DNA trace individual lineages, matrilineal and patrilineal, respectively. They do not mix or recombine at each generation. Hence, they can identify different population migrations. The descendants of the sub-Saharan Africans who first began the Great Diaspora about 70 millennia ago can be distinguished from the sub-Saharan groups who helped to re-colonize Europe after the glaciers melted 16 millennia ago, and from sub-Saharans people who crossed or went around the Mediterranean in Egyptian or Roman times or thereafter as slaves, soldiers, or traders. Although mtDNA and Y DNA can quantifiably estimate a modern population's overall admixture, the approach cannot measure an individual's genealogy. You had about a million ancestors alive in the year 1500, but only two of them carried your mtDNA and Y DNA. Differences between the patterns of mtDNA and Y DNA can suggest why populations migrated: military conquest tends to propagate Y lineages but leave mtDNA lineages in place (men conquer, women get raped), mass migrations in search of a new homeland tend to propagate mtDNA and Y lineages equally, and a slave trade tends to propagate mtDNA lineages but leave Y lineages in place (female slaves are encouraged to propagate, males are not).

According to a summary study by Luísa Pereira and others, "African Female Heritage in Iberia: A Reassessment of mtDNA Lineage Distribution in Present Times," ''Human Biology'' (2005) 77.2: 213-229, sub-Saharan mtDNA haplotypes were found at rates of: 0.62% among German-Danish, 1% among British, 2.38% among Albanians, 2.86% among Sardinians, 0.94% among Sicilians.

According to another summary study by A.M. Gonzalez and others, Mitochondrial DNA affinities at the Atlantic fringe of Europe , ''American Journal of Physical Anthropology'' (2003) 120(4): 391-404, sub-Saharan mtDNA haplotypes were found at rates of: 0.1% in Scotland, 0.4% in England, 0.7% in North Germany, 1.4% in France, 2.9% in Galicia, 2.2% in northern Portugal, 4.3% in central Portugal, and 8.6% in southern Portugal. (As you can see from its Table of European mtDNA , these numbers do not not count the L3 haplotype, which might be ancient and so ambiguous.) For comparison, sub-Saharan mtDNA runs about 21.8% in north Africa.

Neutral autosomal markers are DNA fragments that do not affect traits.

Neutral autosomal markers are odd fragments of DNA that do not affect a person's physical traits. Because they are autosomal (within the nuclear DNA that is subject to meiosis), such markers reflect the recombination of paternal and maternal DNA with each generation. Hence, they are less useful than mtDNA or Y DNA in tracking migrations and they are less precise as to time. This makes it hard to tell if any particular marker dates from the 1500-1800 slave trade, or from the post-glacial re-colonization of Europe, or from some time in between. On the other hand, neutral autosomal markers are useful for individual genealogies since they reflect just how much of an individual's genome came from which population group.

Adaptive autosomal markers are those that spread because they enhance survivability.

Adaptive autosomal markers are those that evolved and spread because they enhance survivability. The best-known example is HbS, which produces the sickle-cell trait. This allele emerged in western equatorial Africa shortly after the invention of agriculture and spread to Europe because it confers near immunity to the most lethal form of malaria. There are many other such traits and they have two main advantages for population studies: First, they have been well-studied for centuries, so different strains are easily identified and tracked. Second, because their adaptive advantages are known, their dates of origin and spread are also known to reasonable precision. The main disadvantage of adaptive autosomal markers is that they cannot tell what fraction of a population came from which ancestry. That HbS is found in, say, 10 percent of some European population does not mean that ten percent have sub-Saharan ancestry; it may simply be that many of those lacking the trait in the past died without progeny due to malaria.

THE A. ARNAIZ-VILLENA CONTROVERSY

Among the studies listed at the Various Admixture Studies site is A. Arnaiz-Villena et al., "HLA genes in Macedonians and the sub-Saharan' origin of the Greeks," ''Tissue Antigens'', 2001 Feb;57(2):118-27. According to some, this study on Greece (''Tissue Antigens'') utilized methodology and reached conclusions similar to ones that were decried as invalid and lacking scientific merit by leading geneticists Luigi Luca Cavalli-Sforza , Alberto Piazza , and Neil Risch , in response to a ''Human Immunology'' study on Palestinians and Israelis by a different team headed by Arnaiz-Villena. The aforementioned scientists characterized similar claims which were made in ''Human Immunology'' with regards to Greeks being "''very similar to Ethiopians and east Africans but very distant from other south Europeans''" and the Japanese being "''nearly identical to west and south Africans'' " as "extraordinary", '''"anomalous"''' and '''contradictory to history, geography, anthropology and all prior population-genetic studies of these groups'''. [http://www.nature.com/nature/journal/v415/n6868/full/415115b.html]

It must be understood that the above controversy, which according to Erica Klarreich of the journal ''Nature'' 414, 382 (2001), caused an article on Israelis and Palestinians to be withdrawn "over political content" (click here for details), relates to only one article (in ''Human Immunology''), and which is not listed at the Various Admixture Studies site. The article listed at the Various Admixture Studies site (''Tissue Antigens'') has never been challenged. Even so, at most the dispute affects findings in only one country (Greece). The dispute cannot in any way discredit the dozens of studies listed at the Various Admixture Studies site regarding the rest of Europe.

Regarding Greece, another study has found sub-Saharan DNA in the modern Greek population. According to A. Hajjej et al., "HLA genes in Southern Tunisians (Ghannouch area) and their Relationship with other Mediterraneans." ''European Journal of Medical Genetics'' 2006 January - February 49(1):43-56, "This present study confirms the relatedness of Greeks to Sub-Saharan populations. This suggests that there was an admixture between the Greeks and Sub-Saharans probably during Pharaonic period or after natural catastrophes (dryness) occurred in Sahara."

Yet another study found even stronger traces of sub-Saharan DNA in eastern Europe. According to W.E. Johnson, P.H. Kohn, and A.G. Steinberg, "Gm and Km(Inv) frequencies in two Roumanian populations," ''Human Genetics'' 1977 Nov 10; 39(2): 199-211, "Racial admixture was evidenced by the presence of the Gm1,13,15,16,17 and Gm1,3,5,13,14 haplotypes, which are primarily Mongoloid, and the Gm1,5,13,14,17 haplotype which is primarily Negroid."

Yet another study found that the particular strain of sickle-cell trait found in Greece is identical to the strain found in Benin (western sub-Sarahan Africa) and different from other Mediterranean strains. According to M. Boussiou, D. Loukopoulos, J. Christakis, and P. Fessas, "The origin of the sickle mutation in Greece; evidence from beta S globin gene cluster polymorphisms," ''Hemoglobin'', 1991 15(6): 459-67, "Comparison of the above results with similar surveys in other parts of the world and consideration of various historical events suggest that the beta S mutation was introduced into Greece over the last few centuries by the Saracen raids and/or by settlements of North African slaves brought in by the Arabs, Franks, Venetians, or Ottoman Turks, who have occupied the country over the last millennium."

Yet another study found similar results in Albania. According to E. Boletini, M. Svobodova, V. Divoky, E. Baysal, M.A. Curuk, A.J. Dimovski, R. Liang, A.D. Adekile, and T.H. Huisman, "Sickle cell anemia, sickle cell beta-thalassemia, and thalassemia major in Albania: characterization of mutations," ''Human Genetics'' 1994 Feb 93(2): 182-7, "The beta S haplotype was type 19 (Benin).... A few rare mutations were also found, which might have originated in India, Turkey, Macedonia, and Greece."

Yet another study found sub-Saharan Y chromosome haplotyopes in sample of Greeks from the island of Mitilini evidently springing from a small initial population. According to F. Di Giacomo, F. Luca, N. Anagnou, G. Ciavarella, R.M. Corbo, M. Cresta, F. Cucci, L. Di Stasi, V. Agostiano, M. Giparaki, A. Loutradis, C. Mammi', E.N. Michalodimitrakis, F. Papola, G. Pedicini, E. Plata, L. Terrenato, S. Tofanelli, P. Malaspina, and A Novelletto,"Clinal patterns of human Y chromosomal diversity in continental Italy and Greece are dominated by drift and founder effects," '' Molecular Phylogenetics and Evolution'', 2003 Sep 28(3): 387-95, "Microsatellite data indicate that local increases of haplogroup frequencies can be often explained by a limited number of founders. We conclude that local founder or drift effects are the main determinants in shaping the microgeographic Y chromosomal diversity."

Yet another study found various sub-Saharan autosomal markers in Sicily. According to C.M. Calo et al., "Genetic analysis of a Sicilian population using 15 short tandem repeats," ''Human Biology'', Apr 2003, "Our data seem to confirm the hypothesis of Sandler et al. (1978) that underlines the African contribution to the Sicilian gene pool, because of the high frequencies of Hbs, cDe, and Fy (a-b-). In a paper on mtDNA, Semino et al. (1989) found support for this hypothesis, dating back to the introduction of black slaves by Phoenicians and Romans and to the later influxes of Arab immigrants."

Yet another study shows definite sub-Saharan admixture in Portugal. According to L. Pereira, M.J. Prata, and A. Amorim, "Diversity of mtDNA Lineages in Portugal: Not a Genetic Edge of European Variation," ''Annals of Human Genetics'', 64 (2000), 501, "the detection of L sequences at 7.1% in the mitochondrial pool [seems to support the above-mentioned pattern of admixture with African slaves."

Yet another two studies have confirmed about 8 percent of recent sub-Saharan DNA genetic admixture in southern Portugal and 5 percent of recent sub-Saharan genetic admixture in modern Spain. See Martin Richards and others, "Extensive Female-Mediated Gene Flow from Sub-Saharan Africa into Near Eastern Arab Populations," ''American Journal of Human Genetics'', 72 (2003), 1058-64 and H.B. Corte-Real and others, "Genetic Diversity in the Iberian Peninsula Determined from Mitochondrial Sequence Analysis," ''Annals of Human Genetics'', 60 (no. 4, July 1996), 331-50.

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Sub-saharan Dna Admixture In Europe