Mediterranean Sea as Genetic Barrier

This new study confirms that the Mediterranean Sea has acted as a strong barrier to gene flow through geographic isolation following initial settlements. Samples from (Northern) Italy, Tuscany, Sicily and Sardinia are closest to other Southern Europeans from Iberia, the Balkans and Greece, who are in turn closest to the Neolithic migrants that spread farming throughout Europe, represented here by the Cappadocian sample from Anatolia. But there hasn't been any significant admixture from the Middle East or North Africa into Southern Europe since then.

Genes Mirror Geography Across the Mediterranean Basin

We first used principal components analysis (PCA) to visualize the genotypic distances between studied populations. Populations on the southern and northern coasts of the Mediterranean appear to be separated by the geographic barrier of the Mediterranean Sea. The role of the Mediterranean Sea as a barrier for gene flow among populations was also supported by our analysis using the BARRIER software, which implements Monmonier's maximum difference algorithm. In accordance with this finding...the PCA distribution of the populations closely resembles the geographic map of the countries circling the Mediterranean Sea. On this PCA "map" of populations, the east coast of the Mediterranean Sea is appropriately occupied by the Palestinians and the Lebanese Druze. Yemenites and Bedouins branch out from the Mediterranean populations and are closer to the populations of the Near East.

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Seljuk Turks settled in Anatolia in the 12th century AD; however, the Anatolian Cappadocians we included in this study belong to the population that have kept the religion and the language of the pre-Seljuk Cappadocians and, therefore, most likely carry the genetic makeup of the ancient Anatolians. The only important gene flows from Near East to Europe must have occurred in prehistoric times and, as genetic evidence suggests, the most prominent migrations should have occurred during the Neolithic.

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Although the Southeastern Mediterranean islands seem to have acted as a bridge from Anatolia to Southern Europe, the relatively small degree of gene flow between the African and the European coasts shows that the Mediterranean Sea also had a barrier function as also suggested with studies of mtDNA polymorphisms. Thus, the Mediterranean seems to have facilitated the migrations of Neolithic farmers along its Southern European coast but it mostly acted as an isolating factor between its European and African coasts.

Paschou et al. "Maritime route of colonization of Europe". PNAS, 2014.

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