Distribution of Southern Iberian haplogroup H indicates exchanges in the western Mediterranean

Recent open access paper The distribution of mitochondrial DNA haplogroup H in southern Iberia indicates ancient human genetic exchanges along the western edge of the Mediterranean, by Hernández, Dugoujon, Novelletto, Rodríguez, Cuesta and Calderón, BMC Genetics (2017).

Abstract (emphasis mine):

The structure of haplogroup H reveals significant differences between the western and eastern edges of the Mediterranean, as well as between the northern and southern regions. Human populations along the westernmost Mediterranean coasts, which were settled by individuals from two continents separated by a relatively narrow body of water, show the highest frequencies of mitochondrial haplogroup H. These characteristics permit the analysis of ancient migrations between both shores, which may have occurred via primitive sea crafts and early seafaring. We collected a sample of 750 autochthonous people from the southern Iberian Peninsula (Andalusians from Huelva and Granada provinces). We performed a high-resolution analysis of haplogroup H by control region sequencing and coding SNP screening of the 337 individuals harboring this maternal marker. Our results were compared with those of a wide panel of populations, including individuals from Iberia, the Maghreb, and other regions around the Mediterranean, collected from the literature.

Both Andalusian subpopulations showed a typical western European profile for the internal composition of clade H, but eastern Andalusians from Granada also revealed interesting traces from the eastern Mediterranean. The basal nodes of the most frequent H sub-haplogroups, H1 and H3, harbored many individuals of Iberian and Maghrebian origins. Derived haplotypes were found in both regions; haplotypes were shared far more frequently between Andalusia and Morocco than between Andalusia and the rest of the Maghreb. These and previous results indicate intense, ancient and sustained contact among populations on both sides of the Mediterranean.

Our genetic data on mtDNA diversity, combined with corresponding archaeological similarities, provide support for arguments favoring prehistoric bonds with a genetic legacy traceable in extant populations. Furthermore, the results presented here indicate that the Strait of Gibraltar and the adjacent Alboran Sea, which have often been assumed to be an insurmountable geographic barrier in prehistory, served as a frequently traveled route between continents.

a, b, c. Interpolated frequency surfaces of clade H and its main sub-clades (H1 and H3). Frequencies (%) are showed in a colour scale. See information about the populations used in Additional files 4 and 5. Map templates were taken from Natural Earth free map repository (http://www.naturalearthdata.com/)

I usually find mtDNA data, especially studies like this one based on modern populations, very difficult to interpret for anthropological purposes. It is well-known that there are important differences in the pattern of Y-DNA and mtDNA expansion and distribution.

A paragraph in this respect caught my attention:

The patterns of variation in the Y-chromosome between western and eastern Andalusians, based on 416 males, have also been investigated for a set of Y-Short Tandem Repeats (Y-STRs) and Y-SNPs [53, 54, 55], Calderón et al., unpublished data] in combination to mtDNA analyses ([18, 19] and present study). In general, for both uniparental makers, Andalusians exhibit a typical western European genetic background, with peak frequencies of mtDNA Hg H and Y-chromosome Hg R1b1b2-M269 (45% and 60%, respectively). Interestingly, our results have further revealed that the influence of African female input is far more significant when compared to male influence in contemporary Andalusians. The lack of correspondence between the maternal and paternal genetic profiles of human populations reflects intrinsic differences in migratory behavior related to sex-biased processes and admixture, as well as differences in male and female effective population sizes related to the variance in reproductive success affected, for example, by polygyny [56, 57].

I think that the greater reduction in patrilineal lineages compared to maternal lineages we usually see during and after prehistoric or historic migrations have more to do with the renown Uí Néill family case and with war-related casualties (since combatants were usually men) than with other more popular explanations, such as enslavement of women or polygyny.

The most successful paternal lines (anywhere in the world) were probably those who remained in power for a long time (be it a patriarchal society based on families, clans, or more complex organizational units), who were richer and thus more capable of having healthy offspring, who in turn were able to survive longer and have more children who inherited power, etc.

In case of recent migrations or population movements that disrupt the previously established organization, after a certain number of generations, successful patrilocal families (usually from incoming lineages) might slowly dominate over a whole region, with poorer families (usually of ‘indigenous’ lineages) suffering a greater – especially perinatal and child – mortality, without any obvious (pre)historic event associated to these gradual changes.

This gradual replacement of paternal lineages is compatible with the adoption of the native language by newcomers. If the number of migrants is greater that the native population, and especially if their technology is more advanced, then a more radical change including ethnolinguistic identification is more likely.

I don’t deny the (pre)historic existence of radical replacement of male populations with continuity of female lineages due to massacres of men, female slavery, or polygyny, but they are probably not the main explanation for most regional differences seen in paternal lineages, and should thus be used with caution.

Gradual replacement and founder effects are also the most logical explanation for why autochthonous continuity myths (that the modern regional prevalence of few successful lineages tended to create in the 2000s) haven’t been corroborated by ancient DNA; e.g. R1b-DF27 in Basques, N1c-M178 in Finnic populations, R1a-Z283 in Slavs, etc. There is nothing different in those areas from other recent founder effects and internal migratory flows seen everywhere in Europe in the past millennia.

Paper discovered via a link by Alberto Gonzalez on Facebook group Iberia ADN