Genetic history of the Iberian Peninsula

As is the case for most of the rest of Southern Europe, the principal ancestral origin of modern Iberians are Early European Farmers who arrived during the Neolithic.

[10][11][12] Due to its position on the Mediterranean Sea, like other Southern European countries, there were also contacts with other Mediterranean peoples such as the Phoenicians, Ancient Greeks and Carthaginians who briefly settled along Iberia's eastern and southern coasts, the Sephardi Jewish community, and Berbers and Arabs arrived during Al-Andalus, all of them leaving some North African and Middle Eastern genetic influences, particularly in the south and west of the Iberian Peninsula.

[18][19] Nevertheless over half of both Iberian and Sardinian Iron Age genetic profiles were replaced during the centuries long Punic, Roman Imperial and Islamic dominations, with only the Basques remaining largely unaffected.

These properties include the direct, unaltered inheritance of mtDNA and NRY DNA from mother to offspring and father to son, respectively, without the 'scrambling' effects of genetic recombination.

We also presume that these genetic loci are not affected by natural selection and that the major process responsible for changes in base pairs has been mutation (which can be calculated).

[28] A study published in 2019 using samples of 271 Iberians spanning prehistoric and historic times proposes the following inflexion points in Iberian genomic history:[29] A number of studies have focused on ascertaining the genetic impact of historical North African population movements into Iberia on the genetic composition of modern Spanish and Portuguese populations.

Initial studies pointed to the Straits of Gibraltar acting more as a genetic barrier than a bridge during prehistorical times,[30][31][32] while other studies point to a higher level of recent North African admixture among Iberians than among other European populations,[33][34][35][36][37][38][39] albeit this is as a result of more recent migratory movements, particularly the Moorish invasion of Iberia in the 8th century.

In terms of autosomal DNA, the most recent study regarding African admixture in Iberian populations was conducted in April 2013 by Botigué et al. using genome-wide SNP data for over 2000 European, Maghreb, Qatar and Sub-Saharan individuals of which 119 were Spaniards and 117 Portuguese, concluding that Spain and Portugal hold significant levels of North African ancestry.

[41][42][43][44] However, contrary to past autosomal studies and to what is inferred from Y-Chromosome and Mitochondrial Haplotype frequencies (see below), it does not detect significant levels of Sub-Saharan ancestry in any European population outside the Canary Islands.

In an autosomal study by Spínola et al. (2005), which analyzed the human leukocyte antigen (HLA genes) (inherent in all ancestors in direct paternal and maternal lineages) in hundreds of individuals from Portugal, showed that the Portuguese population has been influenced by other Europeans and North Africans, via many ancient migrations.

"[57] In general aspects, according to (Bosch et al. 2007) "...the origins of the Iberian Y-chromosome pool may be summarized as follows: 5% recent NW African, 78% Upper Paleolithic and later local derivatives (group IX), and 10% Neolithic" (H58, H71).

There is considerable geographic divergence across the peninsula with high frequencies observed for Western Andalusia (14.6%)[63] and Córdoba (8.3%).,[60] Southern Portugal (10.7%), South West Castile (8%).

Adams et al. and other previous publications, propose that the Moorish occupation left a minor Jewish, Saqaliba[64] and some Arab-Berber genetic influence mainly in southern regions of Iberia.

This subclade is found in over 60% of the male population in the Basque Country and 40-48% in Madrid, Alicante, Barcelona, Cantabria, Andalucia, Asturias and Galicia.

Subsequent in-migration by members of other haplogroups and subclades of R1b did not affect its overall prevalence, although this falls to only two thirds of the total R1b in Valencia and the coast more generally.

[73][74][75] R-S28/R-U152 is slightly significant in Seville, Barcelona, Portugal and Basque Country at 10-20% of the total population, but it is represented at frequencies of only 3.0% in Cantabria and Santander, 2.0% in Castille and Leon, 6% in Valencia, and under 1% in Andalusia.

In general, a typical Western European haplogroup or Atlantic modal haplotype (AMH) composition was found in mainland Portugal, associated to high level of mitochondrial genetic diversity.

The typing of extra coding region SNPs has provided the refinement or confirmation of the previous classification obtained with EMMA tool in 96% of the cases.