Gene study shows Spain's Jewish and Muslim ancestry

By Nicholas Wade

Published: December 5, 2008

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The genetic signatures of people in Spain and Portugal provide new and explicit evidence of the mass conversions of Sephardic Jews and Muslims to Catholicism in the 15th and 16th centuries after Christian armies wrested Spain back from Muslim control, a team of geneticists reports.

Twenty percent of the population of the Iberian Peninsula has Sephardic Jewish ancestry and 11 percent have DNA reflecting Moorish ancestors, the geneticists have found. Historians have debated how many Jews converted and how many chose exile. "One wing grossly underestimates the number of conversions," said Jane Gerber, an expert on Sephardic history at the City University of New York.

The finding bears on two different views of Spanish history, said Dr. Jonathan Ray, a professor of Jewish studies at Georgetown University. One, proposed by the 20th-century historian Claudio Sánchez-Albornoz, holds that Spanish civilization is Catholic and other influences are foreign; the other sees Spain as having been enriched by drawing from all three of its historical cultures, Catholic, Jewish and Muslim.

The study, based on an analysis of Y chromosomes, was conducted by biologists led by Mark Jobling of the University of Leicester in England and Dr. Francesc Calafell of the Pompeu Fabra University in Barcelona. They developed a Y chromosome signature for Sephardic men by studying Sephardic Jewish communities in places where Jews migrated after being expelled from Spain in 1492 to 1496. They also characterized the Y chromosomes of the Arab and Berber army that invaded Spain in A.D. 711 from data on people living in Morocco and Western Sahara.

After a period of forbearance under the Arab Umayyad dynasty, Spain entered a period of religious intolerance, with its Muslim Berber dynasties forcing Christians and Jews to convert to Islam, and the victorious Christians then expelling Jews and Muslims or forcing them to convert. The new genetic study, reported online on Thursday in the American Journal of Human Genetics, indicates there was a high level of conversion among Jews.

Because most of the Y chromosome remains unchanged from father to son, the proportions of Sephardic and Moorish ancestry detected in the present population are probably the same as those just after the 1492 expulsions. A high proportion of people with Sephardic ancestry was to be expected, Ray said. "Jews formed a very large part of the urban population up until the great conversions," he said.

Ray raised the question of what the DNA evidence might mean personally. "If four generations on I have no knowledge of my genetic past, how does that affect my understanding of my own religious association?"

The issue is one that has confronted Calafell, an author of the study. His own Y chromosome may be of Sephardic ancestry — the test is not definitive for individuals — and his surname is from a town in Catalonia; Jews undergoing conversion often took surnames from place names. But he does not regard his Y chromosome as a strong link to the Sephardic heritage. Assuming no in-breeding, he would have had more than one million living ancestors in A.D. 1500. "My full ancestry is made of many different individuals, and my Y chromosome tells me just about one of them," he said.