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The ancestry of modern Iberians (Spanish and Portuguese) is consistent with the geographical situation of the Iberian Peninsula in the south-west of Europe:There is a strong connexion particularly with Atlantic Europe but also Mediterranean Europe and the Near East, albeit the latter is lesser than other Mediterranean countries (notably Greece) due to Spain being the furthest away from the Bosphorous region considered the main bridge of Neolithic expansions into Europe. Nevertheless, Iberia has the strongest link in Europe to both North African and Sub Saharan Africa, purportedly as a result of northward population movements during the seven centuries of Muslim rule over the peninsula. Iberia's Mediterranean and Near Eastern connexion is also likely to be largely of historical rather prehistorical origin, with the region's prehistorical ancestral basis being fundamentally western European.

Population Genetics: Methods and Limitations

One of the first scholars to perform genetic studies was Luigi Luca Cavalli-Sforza. He used classical genetic markers to analyse DNA by proxy. This method studies differences in the frequencies of particular allelic traits, namely polymorphisms from proteins found within human blood (such as the ABO blood groups, Rhesus blood antigens, HLA loci, immunoglobulins, G-6-P-D isoenzymes, among others). Subsequently his team calculated genetic distance between populations, based on the principle that two populations that share similar frequencies of a trait are more closely related than populations that have more divergent frequencies of the trait.

Since then, population genetics has progressed significantly and studies using direct DNA analysis are now abundant and may use mitochondrial DNA (mtDNA), the non-recombining portion of the Y chromosome (NRY) or autosomal DNA. MtDNA and NRY DNA share some similar features which have made them particularly useful in genetic anthropology. 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).

The smaller effective population size of the NRY and mtDNA enhances the consequences of drift and founder effect, relative to the autosomes, making NRY and mtDNA variation a potentially sensitive index of population composition. These biologically plausible assumptions are not concrete, Rosser suggests that climatic conditions may affect the fertility of certain lineages.

The underlying mutation rate used by the geneticists is more questionable. They often use different mutation rates and studies frequently arrive at vastly different conclusions. NRY and mtDNA may be so susceptible to drift, that some ancient patterns may have become obscured. Another assumption is that population genealogies are approximated by allele genealogies. Barbujani points out that this only holds if population groups develop from a genetically monomorphic set of founders. Barbujani argues that there is no reason to believe that Europe was colonized by monomorphic populations. This would result in an overestimation of haplogroup age, thus falsely extending the demographic history of Europe into the Late Paleolithic rather than the Neolithic era. (See also Genetic drift, Founder effect, Population bottleneck.) Greater certainty about chronology may be obtained from studies of ancient DNA (see below) but so far these have been comparatively few.

Whereas Y-DNA and mtDNA haplogroups represent but a small component of a person’s DNA pool, autosomal DNA has the advantage of containing hundreds and thousands of examinable genetic loci, thus giving a more complete picture of genetic composition. Descent relationships can only to be determined on a statistical basis, because autosomal DNA undergoes recombination. A single chromosome can record a history for each gene. Autosomal studies are much more reliable for showing the relationships between existing populations but do not offer the possibilities for unraveling their histories in the same way as mtDNA and NRY DNA studies promise, despite their many complications.

Genetic studies operate on numerous assumptions and suffer from methodological limitations such as selection bias and confounding. Phenomenon like genetic drift, foundation and bottleneck effects cause large errors, particularly in haplogroup studies. No matter how accurate the methodology, conclusions derived from such studies are compiled on the basis of how the author envisages their data fits with established archaeological or linguistic theories.

Analysis of prehistoric populations

2014 Study

A 2014 genetic study revealed that a Stone age man from the Mesolithic period, who lived in the Iberian Peninsula about 7,000 years ago, had blue eyes, black or brown hair, and dark skin. His DNA proved to be different from the genetic make up of most today's european populations.

Main genetic compositions

Overall Genetic make-up

DNA analysis shows that Spanish and Portuguese populations are most closely related to other populations of western Europe.

According to Dupanloup et al. (2004) the main components in the European genomes appear to derive from ancestors whose features were similar to those of modern Basques (Paleolithic) and Near Easterners (Neolithic), with average values greater than 35% for both these parental populations, regardless of whether or not molecular information is taken into account. The lowest degree of both Basque and Near Eastern admixture is found in Finland, whereas the highest values are, respectively, 70% ("Basque") in Spain and roughly 60% ("Near Eastern") in the Balkans.

However, a controversial study, published in January 2010, claimed that despite this apparent East-West cline, Western Europeans (including Iberians) are of a nearly equal combination of the European hunter gatherers of the earlier Paleolithic period and more recent Neolithic period ancestry from the Near East, that likely came from Anatolia.

Autosomal DNA

A 2007 European-wide study including Spanish Basques and Valencian Spaniards, found Iberian populations to cluster the furthest from other continental groups, implying that Iberia holds the most ancient European ancestry. In this study, the most prominent genetic stratification in Europe was found to run from the north to the south-east, while another important axis of differentiation runs east-west across the continent. It also found, despite the differences, that all Europeans are closely related.

Y-Chromosome DNA

Y-chromosome analysis had suggested Paleolithic ancestry among populations in the Iberian Peninsula and that Iberia may have played a role in the re-population of western Europe after the last glaciation. This shows an ancestral bond between Iberia and the rest of western Europe, and in particular with Atlantic Europe, which share high frequencies of these haplogroups. R1b1a2, the most common western European haplogroup, arose 4,000 to 8,000 years ago in southwest Asia and later spread to Europe.

Mitochondrial DNA

According to Dupanloup et al. (2004) the main components in the European genomes appear to derive from ancestors whose features were similar to those of modern Basques and Near Easterners, with average values greater than 35% for both these parental populations, regardless of whether or not molecular information is taken into account. The lowest degree of both Basque and Near Eastern admixture is found in Finland, whereas the highest values are, respectively, 70% ("Basque") in Spain and roughly 60% ("Near Eastern") in the Balkans.

DNA analysis shows that the Spanish and Portuguese are most closely related to other populations of western Europe: the French, the Andorrans, the Italians, the Irish, the British, the Germans, and the Swiss.

The results suggested that the lineage R1b1a2 (R-M269) (from 2003 to 2005 what is now R1b1a2 was designated R1b3; from 2005 to 2008 it was R1b1c and from 2008 to 2011 it was R1b1b2), like E1b1b or J lineages, spread together with farming from the Near East. Dr Patricia Balaresque added: "In total, this means that more than 80% of European Y chromosomes descend from incoming farmers. In contrast, most maternal genetic lineages seem to descend from hunter-gatherers. To us, this suggests a reproductive advantage for farming males over indigenous hunter-gatherer males during the switch from hunting and gathering, to farming".

Haplogroup composition of the ancient Iberians was very similar to that found in the modern Iberian Peninsula populations, suggesting a long-term genetic continuity since pre-Roman times.

See also

• Genetic history of Europe

References

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2. Milisauskas (2002, p. 58) harvtxt error: no target: CITEREFMilisauskas2002 (help)
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7. Swarthy, blue-eyed caveman revealed using DNA from ancient tooth
8. Blue-Eyed Hunter-Gatherers Roamed Prehistoric Europe, Gene Map Reveals
9. Stone Age Spaniard had blue eyes, dark skin
10. Stone Age Europeans had dark skin and blue eyes, Spanish researchers say
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• Genetics by country
• History of Spain
• History of Portugal by topic