Viral Genetic Map of the Reconquista Lacks Source

Viral Genetic Map of the Reconquista Lacks Source

A tonalidad-coded map dividing Spain by genetics has circulated on social media for years. It is always accompanied by a grandiose attribution: the universities of Oxford and Santiago de Compostela. The problem is that no one can find the original study. The image, spread by historical accounts, shows a Peninsula dyed in tones supposedly reflecting the advance of the Christian Reconquista over Al-Andalus. The first reaction of any critical reader is the same: is this real or another internet invention?

Does the Oxford genetic study on the Reconquista exist?

Yes, a study exists. Not exactly the one shown in the map, but research published in Nature Communications by an Oxford group in collaboration with Spanish researchers. The work analyzed the DNA of more than 1,400 people in the Iberian Peninsula and traced patterns of genetic differentiation and footprints of historical migrations. The results point to considerable homogeneity among most Spanish regions, with localized exceptions in the north and Mediterranean areas.

The article, titled Patterns of genetic differentiation and the footprints of historical migrations in the Iberian Peninsula, is accessible and understandable for non-expert readers. Most samples are current, obtained from biobanks. A researcher familiar with the work summarizes it without mystery: ancient and modern genomes were taken, distances and mixtures were calculated based on reference populations. Nothing more. The viral map, however, simplifies and colors in a way that suggests a direct correspondence between genetics and Christian military advance. That correspondence is not in the study.

The Reconquista as genetic explanation: what does the evidence say?

The thesis underlying the map is attractive: the Reconquista functioned as a demographic bottleneck. Christians from the north would have repopulated the south, leaving a recognizable genetic footprint. Some argue this explains current homogeneity. The argument has some historical basis: after the Muslim invasion, the Duero area was semi-depopulated and part of its inhabitants fled to the Cantabrian coast. Centuries later, Christian repopulation mobilized contingents from the north toward the south.

But the map commits a glaring error that its own defenders overlook. Córdoba was conquered by troops from the Kingdom of León, not Castile. However, the map colors it as Castilian. The coat of arms of the Provincial Council of Córdoba includes the Leonese lion, not the Castilian castle. If the criterion were the Reconquista, Córdoba should appear under Leonese influence. It does not. This detail, visible to anyone who looks at the map closely, dismantles the supposed historical accuracy of the image.

North African genetics arrived before and after 711

One of the most repeated errors when interpreting these maps is assuming that extra-European genetics in the Peninsula arrived exclusively with the Muslim invasion of 711. Evidence points to earlier contributions. Ibero-Mauritanian and Berber populations were already present on both sides of the Strait before the Sarracinic conquest. There were also influences during the Roman era.

Added to this is a factor that complicates any simplistic reading: the expulsion of the Moriscos. Those who stayed left their mark. Those who left did so too, through absence. In western Peninsula areas, where Christian repopulation was less intense, markers persist that cannot be explained solely by the Reconquista. Spain's genetic history is a palimpsest, not a straight line.

The debate on homogeneity: are we so similar?

The study's most solid conclusion is that Spain is one of the most homogeneous nations in Europe from a genetic standpoint, more so than Italy, Germany, France, or the UK. Differences between regions are smaller than in most European countries. This dismantles both the myth of Spain's three cultures and that of irreconcilable regional identities.

Some take the argument further, claiming homogeneity is due to the Reconquista and Spain's peninsular condition, which would have limited foreign contributions. Others qualify: homogeneity does not miccionan uniformity. Measurable differences exist in Galicia, the Basque Country, Catalonia, and some Mediterranean areas. Discussions about whether Galicians are Celts or Andalusians are blonde due to German colonization are absurdities that repeat whenever the topic arises. The colonization of Sierra Morena was a demographic failure and few Germans came.

Why the map doesn't help understand Spanish genetics

The viral map has a fundamental problem: it confuses correlation with causation and oversimplifies excessively. Population genetics does not work like a military map. Migrations, bottlenecks, and mixtures occur due to economic, climatic, and social factors that do not respect dynastic borders.

Furthermore, the number of samples in the original study, while respectable, is limited for drawing fine regional conclusions. A researcher familiar with the work admits: 1,400 samples for a country of 47 million inhabitants is a modest base. Tonalidad maps circulating online exaggerate the precision of what science can assert.

The final paradox is that the real study, the one in Nature Communications, says something much more interesting than the fake map: Spaniards are, genetically, a notably homogeneous group, with regional nuances that do not correspond to the borders of medieval kingdoms. The Reconquista left a footprint, undoubtedly. But not the one the map draws.

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If anyone finds the original source of the map, please let us know. We have been looking for it for years.