Common ancestry in the Mediterranean

Just a couple of items I spotted on race/history/evolution blog, which I have been shamelessly mining for information today.

Anthropological analysis of neolithic and Early Bronze Age skeletons–a classical and molecular approach (East Slavonia, Croatia).

Hincak Z, Drmić-Hofman I, Mihelić D.

Institute for Mediterranean Heritage, Science and Research Center of Koper, University of Primorska, Koper, Slovenia. zdhincak@inet.hr

Theories about the first Indo-European migration are numerous. Significant contribution in attempt to resolve these theories is given by analysing skeletal material from two biggest prehistoric archaeological sites from N-E Croatia. Eight skeletons of Starcevo culture from sites “Nama” and “Hotel” at Vinkovci (6100-5500 BC) and seven skeletons of Vucedol culture from the site Vineyard Streim at Vucedol near Vukovar (3000-2500 BC) were analysed. Methods of classical anthropological analysis tried to distinguish the differences among members of both populations, while the methods of molecular genetics were used in defining possible genetic structure of both ancient populations. Established differences speak on the behalf of the theory of Maria Gimbutas about the first Indo-European migration with a cattle breeding population from the east around 3500 BC.

X-chromosome SNP analyses in 11 human Mediterranean populations show a high overall genetic homogeneity except in North-west Africans (Moroccans).

Tomas C, Sanchez JJ, Barbaro A, Brandt-Casadevall C, Hernandez A, Ben Dhiab M, Ramon M, Morling N.

Due to its history, with a high number of migration events, the Mediterranean basin represents a challenging area for population genetic studies. A large number of genetic studies have been carried out in the Mediterranean area using different markers but no consensus has been reached on the genetic landscape of the Mediterranean populations. In order to further investigate the genetics of the human Mediterranean populations, we typed 894 individuals from 11 Mediterranean populations with 25 single-nucleotide polymorphisms (SNPs) located on the X-chromosome.

 RESULTS: A high overall homogeneity was found among the Mediterranean populations except for the population from Morocco, which seemed to differ genetically from the rest of the populations in the Mediterranean area. A very low genetic distance was found between populations in the Middle East and most of the western part of the Mediterranean Sea. A higher migration rate in females versus males was observed by comparing data from X-chromosome, mt-DNA and Y-chromosome SNPs both in the Mediterranean and a wider geographic area. Multilocus association was observed among the 25 SNPs on the X-chromosome in the populations from Ibiza and Cosenza.

CONCLUSIONS: Our results support both the hypothesis of (1) a reduced impact of the Neolithic Wave and more recent migration movements in NW-Africa, and (2) the importance of the Strait of Gibraltar as a geographic barrier. In contrast, the high genetic homogeneity observed in the Mediterranean area could be interpreted as the result of the Neolithic wave caused by a large demic diffusion and/or more recent migration events. A differentiated contribution of males and females to the genetic landscape of the Mediterranean area was observed with a higher migration rate in females than in males. A certain level of background linkage disequilibrium in populations in Ibiza and Cosenza could be attributed to their demographic background.

Yet again, decent evidence for a population migration starting in the Eastern part of the Med. the higher migration of females to amles is interesting, as usually Y DNA is more mobile.

2 responses to “Common ancestry in the Mediterranean

  1. On first look at least, I cannot share the conclussions. The Med-only PC graph (fig 1, left)actually seems to show two major differential axis:

    1. Morocco vs. Majorca in the horizontal axis (the rest are neutral for this comoponent). This suggests two things: (a) that Majorca has some sort of founder effect and (b) that Morocco shows some clear differences (no news here: coincident with greatest Y-DNA E in Morocco).

    2. Valencia vs. Turkey. Probably this is PC1 (not clear in the graph) as it represents the East-West axis that I would expect to show up in any analysisi of Mediterranean genetics. The most odd position, I’d say, it’s that of Iraq. Ibiza’s position is well explained by the fact that the small island was a Phoenician colony but Iraq requires another explanation.

    Probably Iraqi specific components have not been detected by PC analysis, allignining instead towards a minor component of its genome. This is way too common in PC analysis and that’s why I strongly prefer K-means structure, specially if deep enough to show the majority of locally relevant components.

    A good contrast is autosomal analysis of European (and Anatolian) genome by Bauchet et al, 2007. In that paper, not only the E-W Mediterranean cline was evident in the PC graph (a matter of luck actually) but also the K-means structure shows clearly that non-Basque Iberians have a dominant component of their own, with the Eastern Mediterranean (Greek, Armenian, Jewish) component being secondary or even tertiary.

    Another criticism could be made in the choice of populations: all Iberian and Italian samples were taken in the areas that may have been more actively affected by Neolithic or post-Neolithic influences from the East. Certainly chosing all Italian samples in Calabria and Sicily, and all Iberian samples in Valencia and the Balearic islands doesn’t seem representative of Mediterranean Western Europe as a whole. It’s like they were from the beginning trying to find the closest possible samples.

    The global PC mapis illustrative of the kind of bias that this kind of analysis can produce: the horizontal axis expresses the differences between East Asia and West Eurasia (and no matter how minimal West Eurasian admixture may be among Nigerians, they clearly will not allign with East Asians preferentially (but Somalians show a more marked West Eurasian affinity anyhow). The vertical axis shows probably differences between Northern Europe (Denmark) and East Africa (Somalia), with Mediterranean populations alligning more with the first but somewhat intermediate.

    One thing I miss is a “materials and methods section”. The size of samples is most important when analyzing this kind of stuff (for instance I imagine that Somalis weight much more than YRI Nigerians, because otherwise the graph would be different but I have no way to know for sure).

    Also it’s noticeable the position of the CEU sample (Caucasoids from Utah). In principle (because of US census declared ancestry) one would expect them to allign best with Danes (most white Utahns have NW European origins and Denmark is important among them) but they do not, not at all. In fact they seem to be in the PC limbo, right on the middle of the graph, even more than the Iraqi sample. I have since long been critical of that CEU sample because it seems to be not representative of West Eurasians nor Europeans. Maybe one reason is that Utahns may have strong founder effects in their history (Mormonland is different), not sure but certainly this study again highlights that they do not even cluster with one of their putative ancestor populations (Danes).

    Finally, a comment re. your post (not sure if this is in the original article). You say that X-DNA represents female ancestry even suggesting a female dominated migratory event. That is not necesarily true: in fact, in Latin America, specially when compared with other markers, it seems to indicated a male mediated continous immigration. Certainly males also carry X-DNA, even if their influence in a stable population would be significatively smaller than that of females but when a repeated male input happens, as in Latin America, the overall result is that they strongly increase the apportion of “foreign” X-DNA.

    In any case, interesing to know about this paper. X-DNA is only slowly being studied and so far the results appear rather contradictory with everything else we know (Latin America excepted). Like in other global comparisons, the lack of samples from South Asia (caused by legal prohibition of exporting Indian DNA, I believe) is a major blank, specially knowing how important was this region in Eurasian dispersal.

  2. Might it be the case that there was plenty of competition and hence fighting/wars between males, reducing the subsequent diversity of Y DNA?

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