The medieval reconquest of Spain from the Moors left a genetic legacy that can be detected today in the DNA of men from the Iberian Peninsula, scientists have discovered.

A high proportion of Spanish and Portuguese males have a genetic profile indicative of North African or Jewish ancestry, according to research that sheds light on the region’s history. As many as one in five has a Y chromosome of apparently Jewish origin, while one in ten has a Y chromosome showing a North African heritage.

“These proportions attest to a high level of religious conversion, whether voluntary or enforced, driven by historical episodes of social and religious intolerance, that ultimately led to the integration of descendants,” said Professor Mark Jobling, of the University of Leicester, who led the research.

After the Fall of the Roman Empire, Spain was ruled from the 5th to the 8th century by the Visigoths, who established a Christian kingdom. In 711, however, an Arab army crossed the Strait of Gibraltar, beginning several centuries of Muslim rule.

The Moors tolerated both Christianity and Judaism, but Christians nevertheless progressively sought to reconquer the peninsula over a period of several centuries known as the Reconquista. When the Christian kingdoms of Aragon and Castile were united in the 1470s under Ferdinand and Isabella, they began the final phase of the Reconquista. The last Moors were expelled from Granada in 1492 by the “Catholic monarchs”, who began to enforce Christian orthodoxy.

Jews and Muslims were forced to convert, and the Inquisition was established to persecute as heretics those who maintained their old religions. Many converted Jews, or conversos, and converted Muslims, or moriscos, were expelled.

However, as well as their contributions to architecture, food and culture, they left behind their DNA, the study in the American Journal of Human Genetics reports. It examined the male Y chromosome to chart patrilineal descent. While women have two X chromosomes, men have one X and one Y, and the Y is always inherited from their fathers, remaining intact in the male line from generation to generation.

While the majority of modern Spanish men have a Y chromosome type that is common throughout Europe, a high proportion have profiles that correspond with a converso or morisco background.

Professor Jobling added: “In the long term, Jews and moriscos were either kicked out or were forced to integrate. That’s what we see the effect of now, the integration of their descendants.”

The results also show the extent to which it is possible to trace the impact of historical events through modern DNA.

Similar research has recently shown that the Crusaders may have left a genetic mark on modern Lebanon, where a high proportion of Christian men today have a Y chromosome of European origin.

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