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Incest: Good for the Jews

By Joey Kurtzman / January 1, 2007

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Genetically, Ashkenazi Jews are freaks. For most of Jewish history in Europe, cherem-wielding rabbis and an unwelcoming Gentile world made inbreeding a far more appealing option than intermarriage. As a result, Ashkenazim became what scientists call an “endogamous group,” which is another way of saying that they have been sleeping with their cousins for a thousand years. And because endogamous groups often develop distinctive genetic profiles, nothing gets a population geneticist hotter than incest. Ashkenazim aren’t the only group that has kept outsiders out of the gene pool. Most other such groups, however, are isolated, rural populations, like the Amish or the inhabitants of Australia’s Norfolk Island. Ashkenazim are the best-studied group of cousin-kissers on the planet because they’re convenient. A scientist doesn’t need to trek out to the boonies to do her research when she’s got a million Ashkenazi Jews outside her door in the same city where she lives and works.

So endogamy and cosmopolitanism go a long way towards explaining why Jewish DNA has been the source of a gobsmacking number of important genetic findings. Unfortunately, the news coverage of those findings has focused primarily on the negative: genes that predispose us to Tay-Sachs disease, breast cancer, intestinal disease…and the list goes on.

But not all the startling stories hiding in Ashkenazi DNA are bad. Freakishness has its benefits. Some of our genetic eccentricities are more Übermensch than sissy-pants, more Schwarzenegger than DeVito.

Here’s a brief tour through four of the happier genetic quirks discovered about the Ashkenazi wing of our tribe in recent years.

RESISTANCE TO HIV

Yes, you still need to use condoms. But a significant proportion of Ashkenazi Jews have a mutation in a gene called CCR5, and the most common strain of HIV uses the protein produced by CCR5 to climb inside people’s cells. The mutation prevents HIV from exploiting that protein to gain access. If you get two copies of the mutant gene, then most strains of HIV will have little to no chance of getting into your cells. If you get one copy, you’re still less likely to contract HIV, and, if you do, your prognosis is better.

The number of Ashkenazi Jews who have the mutation varies among different Jewish subgroups. According to a study conducted at the Center of Neurogenetics in Paris, a whopping 45 percent of Litvaks (Jews from Lithuania) have at least one copy of the mutation. Ethiopian Jews, on the other hand, don’t have it at all.

Population geneticists aren’t sure why Jews have the mutation in such high numbers. Some of the microbes responsible for Europe’s plagues may have used the same protein, and, as one theory goes, the plagues hit Jews harder than most other European populations, leaving us with a genetic advantage today. Wearing the same heavy clothes every day and never bathing may have had its benefits.

LOW RATES OF ALCOHOLISM

“Shicker iz a goy, shicker iz a goy, shicker iz er, trinken muz er, vahl er iz a goy!” That racist old Yiddish ditty translates: “The goy is a drunk! The goy is a drunk! He has to drink, because he’s a goy!” Classy stuff.

Jews made a mint in Europe by distilling alcohol and selling it to Gentiles, and then we sang songs about what drunks they were. But it turns out Gentiles really are more likely than Jews to become drunks, and it’s not because young Jews learn how to drink responsibly by quaffing Manischewitz at the Seder table, or any of the other old, folk explanations.

Twenty percent of Ashkenazi Jews have a genetic mutation on chromosome nine that causes an unpleasant reaction to alcohol—headaches, nausea, flushing—which in turn makes heavy drinking and alcoholism less likely. This mutation is almost nonexistent among non-Jewish Europeans, but common among Asians.

It’s a model minority thing, apparently.

LOW RATES OF CERVICAL CANCER

It’s not cause you’re not a slut, that’s for sure. The low incidence of cervical cancer among Jewish women has been a longstanding mystery to scientists. People used to think that a circumcised penis was like a magic wand, protecting Jewish women from a nasty cancer that was far more common among non-Jews. That partly explains why American Gentiles started doing like the poor biblical boys of Shekhem and slicing off their foreskins. Once all these Gentiles started circumcising their kids, the bad news came in: Low rates of cervical cancer have nothing to do with circumcision.

The low incidence of human papilloma virus (HPV) among Jewish women may partly explain their low rates of cervical cancer. And scientists have recently discovered that a genetic mutation called p53-D12 predisposes some women to cervical cancer; that mutation is rare among Jewish women.

HIGH RATES OF INTELLIGENCE

“The world is riddled—riddled!—with dumb Ashkenazi Jews,” as Leon Wieseltier reminds us. Too true, Leon. But with the tribe’s lineup including Freud, Einstein, and Speed Levitch, and Ashkenazim possessing an exceedingly high mean IQ, Jews have more than their share of smarties. They’ve also got more than their share of neurological disorders such as Tay-Sachs and Gaucher’s disease. According to a recent study at the University of Utah, there’s a connection: The same genes that cause diseases such as Tay-Sachs and Gaucher’s can also help make you a little Einstein.

The genes in question promote the growth of brain cells. Basically, if you get two of those genes, your brain cells will be afflicted by the kind of extreme and disordered cell growth associated with Tay-Sachs. Get only one of those genes and the cell growth within your brain is enhanced, meaning your grandma will never shut up about you at the mah-jongg table. Or so the Utah researchers argue.

The theory attempts to answer the question of what causes higher rates of intelligence among Jews. And as the theory’s premise is clear and testable, we’ll know for certain in a few years whether it’s the right answer. As to the question of why the gene is there in the first place, it’s all conjecture from here on in.

Some think it’s because our smartest guys became big Talmud chachams and got the girls, while the smartest non-Jewish Europeans became priests and spilled their seed into bed sheets. Or, others postulate, maybe it’s because Jews had to pursue talky, cognitively taxing professions because they weren’t allowed to own land or join guilds. Whatever the explanation may be, Jews got the smahts, baby.

N E X T

Do: What do DNA and endogamy mean for Jewish chauvinism – and antisemitism? Leave your comments below. Go: Feel certain that your family tree takes you directly back to King David himself? Then meet thousands of other crazies like yourself at the Eternal House of David Reunion in Jerusalem on May 28-30, 2007. Read: Evolutionary psychologist Steven Pinker wrote [subscription necessary] on Jewish IQ in The New Republic in June 2006. A more controversial evolutionary psychologist Kevin MacDonald has spent a career addressing Jewish group characteristics, which he terms an “evolutionary strategy” to keep tribal chromosomes exclusive. Judith Shulevitz called MacDonald “Evolutionary Psychology’s Anti-Semite” six years ago in Slate.