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African MtDna Signatures in the Iberian Peninsula
This is a long awaited look at the issue, and particularly because they looked at whole mtDna sequences.
Candela L. Hernandez et al:
Early Holocenic and Historic mtDNA African Signatures in the Iberian Peninsula: The Andalusian Region as a Paradigm
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0139784
Abstract
"Determining the timing, identity and direction of migrations in the Mediterranean Basin, the role of “migratory routes” in and among regions of Africa, Europe and Asia, and the effects of sex-specific behaviors of population movements have important implications for our understanding of the present human genetic diversity. A crucial component of the Mediterranean world is its westernmost region. Clear features of transcontinental ancient contacts between North African and Iberian populations surrounding the maritime region of Gibraltar Strait have been identified from archeological data. The attempt to discern origin and dates of migration between close geographically related regions has been a challenge in the field of uniparental-based population genetics. Mitochondrial DNA (mtDNA) studies have been focused on surveying the H1, H3 and V lineages when trying to ascertain north-south migrations, and U6 and L in the opposite direction, assuming that those lineages are good proxies for the ancestry of each side of the Mediterranean. To this end, in the present work we have screened entire mtDNA sequences belonging to U6, M1 and L haplogroups in Andalusians—from Huelva and Granada provinces—and Moroccan Berbers. We present here pioneer data and interpretations on the role of NW Africa and the Iberian Peninsula regarding the time of origin, number of founders and expansion directions of these specific markers. The estimated entrance of the North African U6 lineages into Iberia at 10 ky correlates well with other L African clades, indicating that U6 and some L lineages moved together from Africa to Iberia in the Early Holocene. Still, founder analysis highlights that the high sharing of lineages between North Africa and Iberia results from a complex process continued through time, impairing simplistic interpretations. In particular, our work supports the existence of an ancient, frequently denied, bridge connecting the Maghreb and Andalusia."
They're much clearer in the actual body of the paper, where they posit two peaks of migration, one about 10,000 ybp, and one in the historic era.
Thus, the most parsimonious model for the oldest demographic events and migrations across the Mediterranean Basin, based on mtDNA evidence, is the following: after 20 ky, U6 lineages had an extensive population expansion in northwest Africa, associated with the emergence of the Iberomaurusian industry in the Maghreb; this pool was further enriched by sub-Saharan L lineages, especially L1b, which began to arrive in North Africa in the beginning of the African Humid Period (AHP, ~11–5.5 ky BP) [57]; U6 and L lineages were introduced from northwest Africa into Iberia in the post-glacial period, most probably by the time of the Younger Dryas/beginning of the Holocene. The opening of the trans-Saharan communications with the African Humid Period, also allowed the southern migration of U6 sequences, and its local expansion as detected in the BSP for lineages observed in sub-Saharan Africa.
"The recent migration peaks identified in the FA of U6 and L lineages could be associated with the Islamic rule of Iberia and the slave trade period, respectively. The HVS-I FA attributes a comparatively lower proportion of these recently introduced sequences into Iberia when compared with the post-glacial one: 1/3 vs 2/3, respectively. The analysis performed by [26] on the phylogeography of L sequences observed in Iberia and remaining Europe pointed to 65% of its introduction in recent times (Romanization period, Islamic expansion and Atlantic slave trade), and 35% at older times, as earlier as 11ky. The complete sequence based FA for U6 agrees more with these results, attributing a half-half proportion of sequences in both periods, showing the higher resolution of complete mitogenomes. The historical-based expectation of a higher proportion of newly introduced U6 lineages in Andalusia was confirmed: 70% against 30% in the earlier migration."
Put more simply,based on the complete sequences and phylogeography, the split would be 50/50 ancient and modern, except for Andalusia, where it's a 30/70 ancient/historical era mix.
What I don't think is totally explained is the split between Western and Eastern Andalusia, unless there was a differing migration during the relocations after the Reconquista:
"Western Andalusians from Huelva show a distinctive African influence (11.8% of the total mtDNA variability) compared to those from the eastern part of the region (Granada province) where the proportion of African maternal haplogroups is much less pronounced (3.6%)".
They also used a very extensive collection of mtDna from all around the Mediterranean Basin to do some contour maps not only of U6a and L1b, which are in the body of the paper, but of all the African mtDna.
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