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Thread: The genomic history of the Iberian Peninsula over the past 8000 years122 days old

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    Default The genomic history of the Iberian Peninsula over the past 8000 years

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    Fig. 2. Genome-wide admixture proportions using qpAdm.

    By ~2000 BCE, Copper Age Iberian Y-DNA haplogroups (I2, G2, and H) were almost completely replaced by R1b-M269, which represents people with Steppe ancestry. David Reich previously talked about this population turnover in Iberia in one of his lectures.

    From the Bronze Age (~2200–900 BCE), we increase the available dataset (6, 7, 17) from 7 to 60 individuals and show how ancestry from the Pontic-Caspian steppe (Steppe ancestry) appeared throughout Iberia in this period (Fig. 1, C and D), albeit with less impact in the south (table S13). The earliest evidence is in 14 individuals dated to ~2500–2000 BCE who coexisted with local people without Steppe ancestry (Fig. 2B). These groups lived in close proximity and admixed to form the Bronze Age population after 2000 BCE with ~40% ancestry from incoming groups (Fig. 2B and fig. S6). Y-chromosome turnover was even more pronounced (Fig. 2B), as the lineages common in Copper Age Iberia (I2, G2, and H) were almost completely replaced by one lineage, R1bM269. These patterns point to a higher contribution of incoming males than females, also supported by a lower proportion of nonlocal ancestry on the X-chromosome (table S14 and fig. S7), a paradigm that can be exemplified by a Bronze Age tomb from Castillejo del Bonete containing a male with Steppe ancestry and a female with ancestry similar to Copper Age Iberians. Although ancient DNA can document that sex-biased admixture occurred, archaeological and anthropological research will be needed to understand the processes that generated it.
    North African ancestry was more widespread in Iberia during the Roman period (about 20 B.C. to 400 A.D.) than previously thought. The genetic influences occurred well before North Africans conquered Iberia during the 8th century A.D.

    Gene flow from North Africa continued into the Muslim period, as is clear from Muslim burials with elevated North African and sub-Saharan African ancestry (Fig. 2D, fig. S4, and table S22) and from uniparental markers typical of North Africa not present among pre-Islamic individuals (Fig. 2D and fig. S11). Present-day populations from southern Iberia harbor less North African ancestry (25) than the ancient Muslim burials, plausibly reflecting expulsion of moriscos (former Muslims converted to Christianity) and repopulation from the north, as supported by historical sources and genetic analysis of present-day groups (25). The impact of Muslim rule is also evident in northeast Iberia in seven individuals from Sant Julià de Ramis from the 8th to 12th centuries CE who, unlike previous ancient individuals from the same region, show North African– related ancestry (Fig. 2C and table S19) and a complete overlap in PCA with present-day Iberians (Fig. 1D).
    Visigoths carried East Eurasian mtDNA haplogroup C4a1a, which was also found in Early Medieval Bavaria. Haplogroup C is primarily found in Northeast Asia, including Siberia.

    In contrast to the demographic changes in the Classical period, movements into Iberia during the decline of the Roman Empire had less long-term demographic impact. Nevertheless, individual sites—for example, the 6th century site of Pla de l'Horta in the northeast—bear witness to events in this period. These individuals, archaeologically interpreted as Visigoths, are shifted from those at L'Esquerda in the direction of Northern and Central Europe (Figs. 1D and 2C and table S18), and we observe the Asian mitochondrial DNA (mtDNA) haplogroup C4a1a also found in Early Medieval Bavaria (20), supporting a recent link to groups with ancestry originally derived from Central and Eastern Europe.
    Last edited by ThirdTerm; 2019-03-18 at 00:24.

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