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Nosing out fact from fiction

Science's take on the biggest Jewish genetic myths of all time

We’ve all heard the generalizations and stereotypes. In its Genes and Religion issue, Moment magazine took a closer look at some of the persistent rumors to find out the truth. A version of that article, edited to conform to The Jewish Standard’s style, appears here with Moment’s permission.

Myth: Jews are a race

It depends on whom you ask

Alhough many now believe the idea is passé, the thorny question of what constitutes race – or if it even exists – is fraught with political, economic, and social implications. The concept largely came into being in the 17th century as colonizing Europeans began to classify human beings based on such physical differences as skin color, head shape, hair texture, and eye color. One of the first to publish reflections on the subject was a French physician, François Bernier, in 1684. A century later, others followed suit – among them Carolus Linnaeus, inventor of zoological taxonomy. The first canonized definition of Jews as a race appeared earlier, in 15th-century Spain, with the blood purity laws established in Toledo by the Catholic Church. The 1442 laws dictated that conversos – Jews who had converted to Christianity – could not hold ecclesiastical roles and certain other jobs within the government and church because they still carried Jewish blood. This marked the “first time in any European laws that there was a kind of definition of religious difference as biological,” said Rachel Burk, professor of Spanish and Portuguese at Tulane University, suggesting that the Catholic Church was instrumental in the creation of the concept of race.

Myth: Genes can reveal religion

Well, sort of, maybe

The DNA of any two people on Earth is, on average, 99.9 percent identical, but that 0.1 percent leaves a lot of room for variation. It is that variation that provides clues to a person’s ancestry. Jews, for example, are identifiable through genetic analysis – as accurately as being able to tell if a person is half-Jewish, or possibly even a quarter Jewish, said Neil Risch, director of the University of California, San Francisco’s Institute for Human Genetics. The clues are not genes, but mutations that are found in higher frequency in some groups than in others. These mutations largely occur in parts of the DNA with no specific function, but they can lead to diseases such as Tay-Sachs or dysautonomia.

Mutations are the result of two genetic phenomena known as founder effect and bottleneck effect. A founder effect occurs when a new population emerges as a result of migration or some other cause; a genetic bottleneck, on the other hand, occurs when an already existing population shrinks due to a cataclysmic event, such as a famine or massacre. In populations in which people marry within a small group, both genetic events lead to fluctuations in frequencies of genetic mutations. The DNA of those who survive continues into the future, while the DNA of those who do not becomes extinct.

Ashkenazi Jews are a good example of a people with this experience: Two major genetic bottlenecks or founder effects seem to have occurred in their history, one around the year 900 C.E. and a second during the 14th century, both likely tied to persecution and immigration. These events narrowed the genetic range of Ashkenazi Jewry.

The key to genetic similarities among people, Risch said, is not religion but endogamy – the practice of marrying within a specific group, which leads to its genetic differentiation. “Endogamy can be tied to religion as a social phenomenon,” he said, but “there’s endogamy that’s not just religious. You can end up with limited mating groups that have nothing to do with religion that have founder effects.”

Risch cites French-Canadians, for example, who are Catholic, but who also carry Tay-Sachs disease – the result of endogamous behavior when the small group settled in Canada. “It is very much a universal phenomenon,” he said.

For the rest of this story, go to http://momentmag.com/moment/issues/2012/08/momentmythbusters.html

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