12 January 2010

DNA: Portuguese conversos' genetic identity

"How has a small Portuguese Jewish community retained its genetic identity," is the title of a recent Haaretz story, concerning a new genetic study recently published in the American Journal of Physical Anthropology.

Of course, the writer meant a Converso or Crypto-Jewish community. Those of us with interests in Sephardic, Converso and crypto-Jewish history, as well as DNA and genetics, answered the question posed by this story rather quickly: How about not marrying others with different backgrounds?

Tracing the Tribe asks why this is always so surprising to people who don't know or don't want to believe the history of these communities? In various Southwestern US states, the same marriage pattern prevails in many families of Jewish descent. Even though they do not declare themselves public Jews, they tend to only marry others "like" themselves. We know what "like" means - why don't these scientists?

A genetic analysis of northern Portuguese crypto-Jews recently yielded a mysterious discovery: It exposed an isolated Jewish community that has somehow retained its genetic identity for centuries - while avoiding the inbreeding that usually occurs in such situations.

Now scientists are trying to understand how these Jews managed to bypass a condition which worries most small, closed Jewish communities in the world.

The new study by researchers from Porto and Coimbra Universities showed that Jews from the Braganca area are genetically closer to Middle Eastern Jews than to the surrounding Portuguese - even after living there for 500 years. This emerged from an analysis of the Y chromosome, which is passed exclusively from father to son with negligent recombination.

[NOTE: What is more interesting is that the article indicates in several places that there appears to be a larger converso population than these small communities indicate. They retained their genetic identity without inbreeding, meaning that the pool of individuals is much larger. While earlier studies indicated that Spain's genetic analysis showed some 2o% of Jewish descent, Portugal's should be similar.]

The story indicates that genetic match was observed also in the Jews of Belmonte, a small town about 200 kilometers south of Braganca. This study is the first time that the genetic makeup of northern Portuguese Jews had been analyzed.

[NOTE: Anyone reading up on Sephardic Jewish history and the Inquisition knows that many Jews escaping the 1492 Exile went through Braganca into Portugal where they thought they would be safe, although it was short-lived.]

However, the genetic analysis of Belmonte Jews showed a dramatic drop in genetic diversity, indicative of inbreeding. This is normal for isolated communities, simply because less genetic material is introduced each generation.

"All small-sized gene pools tend to lose diversity, but the communities from the Braganca area have succeeded in maintaining a very high diversity, with a relatively small non-Jewish introgression," said Professor Antonio Amorim, a
geneticist from the University of Porto who performed the research.

The recently published - a few weeks ago - research in the American Journal of Physical Anthropology showed paternal lineages of 57 unrelated males of established Jewish origins from around Braganca.

A high lineage diversity was found, at both haplotype and haplogroup levels (98.74 and 82.83%, respectively), demonstrating the absence of a strong genetic drift, the research said. Professor Amorim was surprised at both the low level of inbreeding and the retention of Jewish genes.

[NOTE: Tracing the Tribe knows that if you marry only others with your same background in a small number of local families or "similar" families in a wider geographic region, the Jewish genetic identity will be retained.]

"These results can only be explained assuming that the effective size of the population is much greater that it would seem at the first sight," Amorim concluded, "and/or that there is a reproductive strategy minimizing the loss of male lineages but not avoiding totally the input of non-Jewish males."

The research team indicates that "a deeper and more detailed investigation is required to clarify how these communities avoided the expected inbreeding caused by over four centuries of religious repression." The team is still waiting for the mtDNA (maternal DNA).

[NOTE: Considering the fact that women were the leaders of the Belmonte community for centuries and kept the spark of Judaism alive, and that converso communities around the world often have matriarchal leaders who preserve tradition and knowledge, Tracing the Tribe expects that mtDNA results will show the same Jewish connection.

Jews have lived around Braganca since the late 12th century at least, but the major influx was after the 1492 Expulsion during the Inquisition. At first, they thought they would be safe, and they were for a few years, but then Portugal demanded, as Spain had done, that they convert to Catholicism. Some left again, some had their children forcibly kidnapped (and sent to Sao Tome Island, where many died) to force the parents to convert, and larger numbers converted publicly, but maintained their adherence to Judaism in secret.

Over the centuries, without interaction with established Jewish communities, the people lost much of their Jewish knowledge but maintained what they knew. The families in this genetic study are part of that community.]

Michael Freund, head of Shavei Israel, says that thousands of people - in Portugal and elsewhere - are turning towards Judaism as they believe they are descendants of crypto-Jews.

"This study demonstrates the extent to which the Jews of Portugal who were forcibly converted more than five centuries ago sought to preserve their Jewishness down through the generations," he said. "They made heroic efforts to sustain their Jewish identity in secret, and many only married among themselves, as the findings of this study indicate," he said.

Read the complete story at the link above.


  1. Anonymous7:32 AM

    This is a fascinating story. Thank you for bring the article to our attention.


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  3. Anonymous6:59 PM

    My brother had his DNA test done and it showed 28 matches to Belmonte, Portugal on our mtDNA line. What do you think this means?