Fine scale population structure of Spain and the genetic impact of historical invasions and migrations.
C. Bycroft1 ; C. Fernandez-Rozadilla1,2 ; A. Carracedo2 ; C. Ruiz-Ponte2 ; I. Quintela-García3 ; P. Donnelly1,4 ; S. Myers1,4
As well as being linguistically and culturally diverse, the Iberian Peninsula is unusual among European regions in that its demographic history includes a prolonged and large-scale occupation by people of predominately north-west African origin. Therefore, the Iberian Peninsula provides a unique opportunity for studying fine-scale population structure and admixture, and to test cutting-edge methods of detecting complex or subtle population genetic patterns.Previous studies using Y-chromosome, mtDNA as well as autosomal data have detected limited genetic structure in Iberia. However, powerful new methods and larger datasets mean it has recently become possible to detect and characterise genetic differentiation at a sub-national level. We performed the largest and most comprehensive study of Spanish population structure to date by analysing a dataset of ~1,400 Spanish individuals typed at ~700,000 SNPs. Using the fineSTRUCTURE method we detected striking and rich patterns of population differentiation within Spain, at scales down to tens of kilometres. Strikingly, the major axis of genetic differentiation in Spain runs from west to east, while conversely there is remarkable genetic similarity in the north-south direction.To infer details of historical population movements into Spain, we analysed Spain alongside a sample of ~6,000 individuals from Europe, North Africa, and sub-Saharan Africa. Across Spanish groups, we identify varying genetic contributions from north-west African ancestral populations, at times that all fall within the period of Islamic occupation. We also identify Basque-like admixture within Spanish groups to the south of the Basque-speaking region, implying southerly gene flow from this region. This analysis has revealed details of the strengths and weaknesses of different approaches to investigating population genetic history, as well as providing important new insights into the complex genetic history of Spain.
ReplyDeleteEverything is well known and maybe the aspects worthier of noticing are the "two axis": differentiation along the West-East and similarity along the North-South (keeping always in mind that this is a fine-grained study).
On the other hand, adscribing all the north african admixture to the moorish occupation, as the abstract states, seems highly improbable, since we know with certainty of other ancestral and pre-historic connections between Iberia and coastal North Africa (and more important than the former, probably). Moreover, the historical record does not support such idea (natives' conversion to islam followed by demographic Reconquista and then, expulsion of moriscos).
On top of these considerations, their own results seem to contradict this affirmation, since it's difficult to find historical processes that could explain the high similarity along the North-South axis were it true a north african ancestry exclusively derived from the islamic occupation.
As a related note it's worth to mention the conspicuous absence of historians in these multidisciplinary studies. It's difficult to make real sense of these complex data without a well informed historical and archeological framework. Perhaps is the lack of reliability and the ideological agenda of so many "scholars" of the "cultural studies / marxist anthropology" sort what is preventing the inclusion of other serious researchers in these papers.