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Abstract
Genetic differences within or between human populations (population structure) has been studied using a variety of approaches over many years. Recently there has been an increasing focus on studying genetic differentiation at fine geographic scales, such as within countries. Identifying such structure allows the study of recent population history, and identifies the potential for confounding in association studies, particularly when testing rare, often recently arisen variants. The Iberian Peninsula is linguistically diverse, has a complex demographic history, and is unique among European regions in having a centuries-long period of Muslim rule. Previous genetic studies of Spain have examined either a small fraction of the genome or only a few Spanish regions. Thus, the overall pattern of fine-scale population structure within Spain remains uncharacterised. Here we analyse genome-wide genotyping array data for 1,413 Spanish individuals sampled from all regions of Spain. We identify extensive fine-scale structure, down to unprecedented scales, smaller than 10 Km in some places. We observe a major axis of genetic differentiation that runs from east to west of the peninsula. In contrast, we observe remarkable genetic similarity in the north-south direction, and evidence of historical north-south population movement. Finally, without making particular prior assumptions about source populations, we show that modern Spanish people have regionally varying fractions of ancestry from a group most similar to modern north Moroccans. The north African ancestry results from an admixture event, which we date to 860 - 1120 CE, corresponding to the early half of Muslim rule. Our results indicate that it is possible to discern clear genetic impacts of the Muslim conquest and population movements associated with the subsequent Reconquista.

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Abstract
Population genomic studies of ancient human remains have shown how modern-day European population structure has been shaped by a number of prehistoric migrations. The Neolithization of Europe has been associated with large-scale migrations from Anatolia, which was followed by migrations of herders from the Pontic steppe at the onset of the Bronze Age. Southwestern Europe was one of the last parts of the continent reached by these migrations, and modern-day populations from this region show intriguing similarities to the initial Neolithic migrants. Partly due to climatic conditions that are unfavorable for DNA preservation, regional studies on the Mediterranean remain challenging. Here, we present genome-wide sequence data from 13 individuals combined with stable isotope analysis from the north and south of Iberia covering a four-millennial temporal transect (7,500–3,500 BP). Early Iberian farmers and Early Central European farmers exhibit significant genetic differences, suggesting two independent fronts of the Neolithic expansion. The first Neolithic migrants that arrived in Iberia had low levels of genetic diversity, potentially reflecting a small number of individuals; this diversity gradually increased over time from mixing with local hunter-gatherers and potential population expansion. The impact of post-Neolithic migrations on Iberia was much smaller than for the rest of the continent, showing little external influence from the Neolithic to the Bronze Age. Paleodietary reconstruction shows that these populations have a remarkable degree of dietary homogeneity across space and time, suggesting a strong reliance on terrestrial food resources despite changing culture and genetic make-up.

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Originally posted by Ish Gebor:
"The north African ancestry results from an admixture event, which we date to 860 - 1120 CE,"

Yep, finally.

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We also detect a genetic footprint of the Muslim invasion, and subsequent centuries
of Muslim rule, itself. Following the arrival of an estimated 30,000 combatants22, a
civilian migration of unknown numbers of people occurred, thought to be mainly
Berbers from north Morocco and settling in many parts of the peninsula22. Our
analysis, alongside previous smaller studies12,23, imply a substantial and regionally
varying genetic impact. Our results further imply that north west African-like DNA
predominated in the migration. Moreover, admixture mainly, and perhaps almost
exclusively, occurred within the earlier half of the period of Muslim rule (Figure 3b).
Within Spain, north African ancestry occurs in all groups, although levels are low in
the Basque region and in a region corresponding closely to the 14th-century ‘Crown
of Aragon’ (Figure 3c). Therefore, although genetically distinct16,22,23, this implies
that the Basques have not been completely isolated from the rest of Spain over the
past 1300 years.

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There is a direct link between Senegal
and Tariq ibn Ziyad’s invasion of Spain in 711. This link
comes from the fact that many of the followers of Tarik
came from the ribats or ‘religious schools’ he had
established in northern Senegal. Troops from these ribats
formed the backbone of Tarik’s army. These African
Muslims ruled much of Spain until 1492. Since M1c is
presently found in Senegal, the carrier of M1c reported by
Gonzalez et al. (2007) in Valencia may be a descendent
of these African ‘Moors’ that ruled Spain for over 700
years.
Sub-Saharan Africans probably spread hg M1c to
Eurasia. Gonzalez et al. (2007) reported that the carriers
of the M1c subset were from Jordan, Senegal and
Valencia. It was revealed above that 1) many of the
Muslim troops in Tarik’s army that conquered Spain in
711 AD, came from Senegal; and 2) many West Africans
after taking the Hajj, visited Jerusalem and settled in the
Middle East. Even if we eliminate the Jordan sample, the
evidence from Valencia and Senegal gives a 67%
probability that M1c originated in Senegal, not Asia or
North Africa because of the historical presence of SubSaharan
Africans in both areas.

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Abstract
Population genomic studies of ancient human remains have shown how modern-day European population structure has been shaped by a number of prehistoric migrations. The Neolithization of Europe has been associated with large-scale migrations from Anatolia, which was followed by migrations of herders from the Pontic steppe at the onset of the Bronze Age. Southwestern Europe was one of the last parts of the continent reached by these migrations, and modern-day populations from this region show intriguing similarities to the initial Neolithic migrants. Partly due to climatic conditions that are unfavorable for DNA preservation, regional studies on the Mediterranean remain challenging. Here, we present genome-wide sequence data from 13 individuals combined with stable isotope analysis from the north and south of Iberia covering a four-millennial temporal transect (7,500–3,500 BP). Early Iberian farmers and Early Central European farmers exhibit significant genetic differences, suggesting two independent fronts of the Neolithic expansion. The first Neolithic migrants that arrived in Iberia had low levels of genetic diversity, potentially reflecting a small number of individuals; this diversity gradually increased over time from mixing with local hunter-gatherers and potential population expansion. The impact of post-Neolithic migrations on Iberia was much smaller than for the rest of the continent, showing little external influence from the Neolithic to the Bronze Age. Paleodietary reconstruction shows that these populations have a remarkable degree of dietary homogeneity across space and time, suggesting a strong reliance on terrestrial food resources despite changing culture and genetic make-up.

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