Monday, August 6, 2012

Myths about Jews mythbusted


The Biggest Jewish Genetic Myths of All Time

We’ve all heard the generalizations and stereotypes. Moment takes a closer look at some of the persistent rumors to find out the truth.

Though 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 humans based on physical differences such as skin color, head shape, hair texture and eye color. One of the first to publish reflections on the subject was French physician François Bernier in 1684. A century later, others—such as Carolus Linnaeus, inventor of zoological taxonomy—followed suit. The first canonized definition of Jews as a race appeared earlier, in 15th-century Spain, with the establishment of blood purity laws by the Catholic Church in Toledo. 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,” says 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.

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’s 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, says 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 don’t 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 CE 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, says Risch, 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,” says Risch, 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,” says Risch.

For centuries, rumors have circulated that Ashkenazi Jews are the descendants of Khazars, a medieval confederation of semi-nomadic Turkic tribes—a view famously articulated in The Thirteenth Tribe, the 1976 book by Arthur Koestler, the well-respected author of Darkness at Noon. The Khazars were led by a semi-religious figure called the khagan, who, according to sources, converted to Judaism along with much of the ruling class around 740 CE, a decision possibly motivated by political expedience in a region flanked by Muslims and Christians. The conversion is documented in Sefer HaEmunot, a 15th-century text by Rabbi Shem Tov ibn Shem Tov, and the philosopher and poet Yehuda HaLevi’s 12th-century book, The Kuzari, which tells of a dialogue between the Khazar king and a Jew asked to guide him through the basic tenets of Judaism. When the Khazar empire collapsed, Koestler argues, the new Jews migrated west—to places like Lithuania, Ukraine, Germany and others, giving birth to Ashkenazi Jewry. Basing his theory on the work of earlier scholars, he hoped to counteract anti-Semitism, but his book was derided by critics. They argued that the theory—which called into question historic claims to the land of Israel—was unsound. Genetic mapping has since laid the controversy to rest. Though the history is murky, it’s clear that all Jews originated in the Eastern Mediterranean, and that over centuries some migrated. “It’s all very speculative,” says Risch. “There’s not a lot of actual history written down, but the belief is that the Ashkenazis derived from settlers who probably came into the Rhineland around the 9th or 10th century and formed this distinct endogamous group.” The 14th-century founder effect was likely also the result of immigration, largely to Lithuania and the surrounding region.

A 2005 study by a team of three anthropologists at the University of Utah argued for an attention-grabbing premise: that the genes that caused four typically Ashkenazi diseases (Tay-Sachs, Gaucher, Niemann-Pick and mucolipidosis type IV) were so prevalent because they were also linked to increased intelligence, an evolutionary benefit for Jews who typically held occupations that demanded mental acuity. Forced primarily into money-lending starting in Europe as early as the 9th century, Jews needed sharper mathematical skills, and the more successful among them, the Utah anthropologists argued in the study published in the Journal of Biosocial Science, tended to have more children, leading to selection of genes that promoted intelligence. These genes, however, had the nefarious side effect of causing the diseases that plague the Ashkenazi community. The argument makes some uneasy, a fact acknowledged by one of the study’s authors, Henry Harpending, who said at the time, “Absolutely anything in human biology that is interesting is going to be controversial,” given the possibility of using such information for promoting the superiority or inferiority of certain groups. The implication that Jews have a higher IQ than other groups is bolstered by the disproportionate number of Ashkenazi Jews who are Nobel Prize winners and world chess champions, say Harpending and the rest of the Utah team. The study also suggests that the Parsis of India, another endogamous group known for economic and intellectual achievement, might be an additional population in which disease and intelligence have an underlying connection; they also suffer from high rates of breast cancer and Parkinson’s disease. 

“It would be hard to overstate how politically incorrect this paper is,” Steven Pinker, cognitive scientist at Harvard, told The New York Times when the study was published. Nonetheless, he said, “it’s certainly a thorough and well-argued paper.” Others disagree, saying that the study, which contained no footnotes and was written in an impassioned tone not typical of academic literature, was not scientifically rigorous enough. “It’s bad science,” Harry Ostrer, medical geneticist at Yeshiva University’s Albert Einstein College of Medicine, toldNew York magazine. “It’s bad genetics and bad epidemiology.” Some of the mutations the study discusses can even lead to mental retardation, says Risch, who adds, “In my view, there is currently no scientific evidence that Jewish achievement or intelligence has a genetic basis.”

It is true that many biblical figures are said to have lived for centuries. But though studies of Ashkenazi Jews may give the perception that Jews live longer than others, that’s not necessarily the case, says Nir Barzilai of Yeshiva University’s Albert Einstein College of Medicine. Ashkenazi Jews are simply studied more frequently than other groups since their homogeneity makes it is easier for researchers to find similarities. Beginning in 1998, Barzilai began to track a group of more than 500 “super agers”—healthy Ashkenazi Jews between the ages of 95 and 122. The results of the Longevity Genes Project, as it is called, found that longevity is connected to genes and some Jews are indeed blessed with good DNA: Researchers identified at least seven markers associated with longevity, including the CETP gene, which protects against dementia and heart disease. And another Jewish population’s longevity may also hold clues to the secrets of aging—a group of dwarfs living in Ecuador believed to be the descendants of Spanish or Portuguese conversos. Jaime Guevara-Aguirre, an Ecuadorean physician, discovered the people—who have Laron syndrome and are generally less than three-and-a-half feet tall—in remote villages. His findings over the past 25 years have shown that those with Laron syndrome almost never got cancer and never developed diabetes, despite not-uncommon obesity. Their health and longevity are believed to be related to a Laron-linked genetic mutation that makes them unable to react to growth hormone. Jews aren’t the only alter kockers. Researchers at Hawaii’s Kuakini Medical Center have tracked a group of Japanese-American men since the 1960s, and discovered that they have a gene known as FOXO, which doubles its possessor’s chance of living to 100.

Studies have borne out what stomachaches have long suggested: Jews are among the many ethnic groups that display increased sensitivity to dairy products. The National Institutes of Health estimate that some 65 percent of all adults have a form of lactose intolerance; the highest rate is among East Asian populations, where nearly 90 percent of adults are sensitive to lactose, though West Africans, Arabs, Greeks and Italians are all particularly prone to the condition. A 1985 study of 110 Jewish Israeli children strengthened the connection between Jews and dairy woes: Nearly 62 percent were lactose malabsorbers. Gastrointestinal troubles like Celiac disease, which makes gluten difficult to digest, are also common among Jews, according to gastroenterologist Joseph A. Murray of the Mayo Clinic. So are irritable bowel syndrome and inflammatory bowel disease (IBD), writes Ernest Abel, professor of obstetrics and gynecology at Wayne State University and author of Jewish Genetic Diseases: A Layman’s Guide. Some geneticists theorize that there might have been historic perks to a sensitive stomach: The affliction may be a defensive response to substances that come in contact with the lining of the digestive system, a selective advantage in unhygienic conditions. This might explain why gastrointestinal troubles are prevalent among Jews, suggests Abel. It may have been a genetic advantage for Jews forced to live in tightly packed, often unsanitary ghettoes.

Manischewitz may be an acquired taste, but that’s not the reason Jews tend to have fewer drinking problems than other groups. A 2002 study conducted by Deborah Hasin of Columbia University shows that at least 20 and as many as 30 percent of Jews carry a genetic mutation that makes them less susceptible to alcoholism. The mutation, called ADH2*2, is believed to increase levels of acetaldehyde, a toxic chemical byproduct of alcohol metabolism that causes headaches, nausea and flushing. The trait is also common among Asians but is very rare in white Europeans. Without this mutation, less acetaldehyde is produced, making drinking a more pleasurable experience. The 2002 study, which focused on 75 Israeli Jews between the ages of 22 and 65, found that ADH2*2 had the strongest effect on Ashkenazis, Jews who had arrived from Russia before 1989, Sephardi Jews and Jews of Middle Eastern and North African descent; less protected by the genetic mutation were more recent Russian immigrants.

The association of Jews with red hair has a long history, dating back even to the Bible, in which rugged Esau and the harp-playing warrior king David were both believed to be redheads. Some more sinister Jews, too, were thought to be “gingers”: Judas and Shylock are often depicted with flaming locks. In fact, the link has become so widespread in popular culture that some believe there are more auburn-haired Jews than there are Irish, those most famous redheads. Not so, says Abel. “Scotland and Ireland have the highest proportion of people with red hair,” he says. The myth may be the result of confounded expectations: “There’s a higher percentage of Jews with red hair than you might expect from the fact that they came from the Middle East and most people in the Middle East have dark hair,” says Abel, though the number appears to be no higher than the approximately four percent of the world’s population who are endowed with red tresses.

Many Jewish families proudly claim to be from the line of King David (himself believed to be descended from Abraham), a link that, without access to the DNA of biblical figures, has traditionally been made through genealogy and family lore. Science can now weigh in for the first time in human history, although it remains imprecise. The strongest genetic evidence linking contemporary Jews to their ancient counterparts has been the discovery of a Y-chromosome connection to the Kohanim. In 1997, Karl Skorecki, a nephrologist and Director of Medical and Research Development at Haifa’s Rambam Medical Center, led a study that found that men who identified as Kohanim shared certain genetic traits passed from father to son on the Y chromosome—results that suggest they may share a single male ancestor, often referred to as Y-chromosomal Aaron, for Moses’s brother, the original Kohen in the Bible. (The identification of this marker has also boosted the credibility of other groups who claim to be descended from ancient Hebrews. The Lemba, a Bantu-speaking group in southern Africa who have long believed that they are the progeny of distant Jews, also have the DNA sequences indicative of Kohen status. This sequence is also found in the tiny population of modern-day Samaritans in Israel. Interestingly, their mitochondrial DNA, passed from mother to child, doesn’t match the mitochondrial DNA of other Jews, leading researchers to believe that the sect is descended from Jewish men who married non-Jewish women after the Assyrians conquered ancient Israel.) 

Jews are not the only ones who trace themselves back to past religious figures. Certain Muslim families claim to be the offspring of the Prophet Muhammad. Three years ago, their claims were strengthened when geneticists discovered an overlapping DNA signature that connects several men who believe themselves to be Muhammad’s descendants. Bennett Greenspan, president and CEO of Family Tree DNA, says that the shared signature “clearly indicated that they were related via a shared common male ancestor. If the claim is true, and they really are descendants of the Prophet, we agreed that these men do indeed share DNA to prove that point.” There is no similar proof that connects Jews back to King David. As of now, no overlapping DNA signature has been found among the many families that claim descent.

It’s just not the Eve you’re thinking of. Testing of mitochondrial DNA, passed from mother to child, has proven that all of humanity—male and female—descends from one female progenitor: mitochondrial Eve, as she is colloquially known. Believed to have lived about 200,000 years ago in East Africa, mitochondrial Eve was not the first woman to exist (or the only woman who lived at the time), but she is the originator of a piece of DNA that, unlike the DNA of her female contemporaries, did not go extinct. All men and women, across countries, continents, ethnicities, religions and other markers of difference, have DNA passed down to them from this mother of humankind.

All humans are related, but several shared genetic mutations suggest that Jews and Palestinians, as well as other Arabs, share a common but distant ancestry. The predominant mutation of cystic fibrosis, one of the most common genetic diseases among Europeans, is known as DeltaF508; the most common mutation of cystic fibrosis among Ashkenazi Jews, however, is one called W1282X—a mutation shared only by Arabs. And LRRK2, a rare Parkinson’s mutation, appears to be carried mainly by Ashkenazi Jews and the Arab population of North Africa. Why the shared mutations? “If you make a two-dimensional geographic map,” says Risch, “and you ask where do Jews fit genetically, they come out in the Eastern Mediterranean—south of Italy and Greece, so they’re somewhere in between southern Europe and the Middle East.” Doron Behar, a population geneticist at the Rambam Medical Center in Haifa, notes that it is hard to thoroughly trace the genetic origins of the heterogeneous Palestinian people, but that “if you’re looking at a global map of genetic distribution, all of the populations of the Levant will fall very close to each other—Palestinians, Bedouins, Druze, Jews, Jordanians, Lebanese.” Still, although Jews have “a closer resemblance to Palestinians than Irish would to Palestinians, they’re not inseparable. They’re clearly separable,” says Risch. According to Behar, inspecting the DNA of Jews and Palestinians at a closer level reveals clusters that separate slightly, with Jews and Druze in one cluster and Palestinians, Bedouins, Jordanians and Saudi Arabians in another.

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