The Chosen Genes: The story of Jewish origins, once the province of historians and religion scholars, is now being told by DNA
April 16, 2012
Adolf Hitler would not have been particularly proud of him, Harry Ostrer says, though he, like the architect of the Holocaust, has developed systematic ways to separate Jews from non-Jews.
The powerful genetic markers of Jewish ancestry that Ostrer has found don’t imply racial inferiority, yet when the population geneticist first published his findings two years ago, one historian told Science magazine that “Hitler would certainly have been very pleased.”
“That comment really bugged me,” says Ostrer, a professor of genetics here at the Albert Einstein College of Medicine, and a Jew himself. It came from Shlomo Sand, a professor at Tel Aviv University whose 2009 book, The Invention of the Jews (Verso Books), argued that Jews arose from converting many local communities in Europe and elsewhere. His argument is contradicted by Ostrer’s work, which shows that geographically and culturally distant Jews still have more genes in common than they do with non-Jews around them, and that those genes can be traced back to the Levant, an area including modern-day Israel.
“It shows we share in a biological tapestry, and are connected by these genetic threads,” Ostrer says. “Bringing up Hitler was overheated and misconstrues my work.” Sand, however, remains an implacable opponent today. “It is a shame for somebody who defines himself as a Jew to look for a Jewish gene,” he writes in an e-mail.
That reaction isn’t the only misconstruction of this fraught topic, Ostrer says. The DNA that he found also tightly linked Ashkenazi and Sephardic Jews, two prominent culturally and geographically distinct groups; commenters immediately began to say this showed the groups were not separate at all. “And that wasn’t what I was saying either,” Ostrer says. Also, the deeply rooted Middle Eastern markers could be used to support Zionist territorial claims—except, Ostrer points out, the same markers can be found in Palestinians as well.
This month during the Passover holiday, as he and other Jews celebrate their escape from a pre-Hitler enslavement, Ostrer is trying to set the record straight in a new book, Legacy: A Genetic History of the Jewish People (Oxford University Press). In it, he traces efforts by himself and others to map both the genes and the culture of Jews as they spread throughout the world, and he shows how the approaches can complement one another. He also takes on the volatile topic of population traits, arguing that it is extremely difficult to ascribe things like higher IQ to Jews (See sidebar on Page B13).
He gets various reactions. Geneticists who are familiar with his work have been enthusiastic. Ostrer’s research is very solid, says Mary-Claire King, a professor of genome sciences at the University of Washington who was the first scientist to use molecular analysis to date the evolutionary split between humans and chimpanzees. “The approach that Harry uses … lets the data speak for itself,” she writes in an e-mail. “It does not group people from different traditionsa priori. The result is that people sort out, based on their genetics.”
Historians are a little more cautious. “It’s possible there was an ancient genetic marker in common to both Ashkenazi and Sephardic worlds,” says David N. Myers, professor of Jewish history at the University of California at Los Angeles. “But I don’t think biological commonality stands in the way of cultural traditions. Minhag, the Hebrew word for customs, is an important part of identity and history. So Jews in France may eat certain foods during Passover and Jews in Spain may eat different things.”
Ostrer is quick to agree with this last point. One of those traditions is on display at the Einstein kosher cafeteria, where diners can tuck into a pastrami burger rather than a bacon cheeseburger. Over lunch, Ostrer points out that he has been drawn to genetics by its capacity to reveal things about populations, not rewrite their history.
Less than a year ago, in fact, that desire pulled him to Einstein, where he is starting a large center for genomic medicine, and away from New York University Medical School, where he had worked for decades but which “has little interest now in genomics,” he says. Ostrer has a tremendous interest. He has been lobbying the New York City Council for half a million dollars to buy four gene-sequencing machines for the medical college. They would be used, he says, to analyze genetic risk factors for diseases like prostate cancer or diabetes in the African-American and Hispanic populations that surround the college in the East Bronx. “The council seemed very receptive to my argument, which is that the poorer people in New York should have access to the most modern medicine,” he says.
His interest in the genetics of Jews also originated in medicine and attempts to understand why certain populations have higher risks of particular diseases, like specific forms of breast cancer. Years ago, while a professor at NYU, Ostrer started a project to identify DNA sequences that marked such populations. The sequences could also indicate how closely such groups were related, a kind of Jewish family tree.
The differing DNA stretches are called haplotypes, and what Ostrer initiated, with several colleagues, was called the Jewish HapMap Project. This kind of genetic tracking is a tricky prospect among a people to whom the word “wandering” is often applied as prefix, a group found throughout Europe, Africa, Asia, Australia, and the New World.
But other researchers had used DNA successfully to trace aspects of Jewish lineages. Most notably, Michael Hammer, a geneticist at the University of Arizona, had used DNA from the Y chromosome—the one that men have and women don’t—to show genetic support for the Bible’s account of a Jewish male priestly caste, the Cohanim. In 1997, Hammer’s team reported that a particular DNA sequence on the Y chromosome could be found in more than 98 percent of men who identified themselves as Cohanim descendents—in America the last name today is usually Cohen—showing that they were indeed related.
One marker on one chromosome, however, isn’t a very powerful way to track a whole population. Yet gene-sequencing technology has come a long way in 15 years. Computers now can swiftly run through hundreds of thousands of DNA markers on all 23 pairs of chromosomes, and do this in different people to identify variations and similarities. That’s the approach Ostrer and his team employ.
Basically, they use these comparisons to build a tree of population groups. If people in two groups share lots of DNA markers, and people in a third group share fewer, odds are that the first groups are more closely related. The third group branched off earlier.
Do this not just for three groups but for many—and with the help of specialized computer programs—and you get a “nearest neighbor joining tree.” It looks a lot like its name: pairs of branches, each close pair representing the closest genetic neighbor, presumably groups that split more recently than the pairs that are widely spaced. The pairs further apart have accrued more genetic variation, both through random mutations that occur over time and through mixing with other populations.
What Ostrer; Gil Atzmon, an assistant professor of genetics at Einstein; and their colleagues described in a 2010 paper, in The American Journal of Human Genetics, was a tree of 17 groups, both Jews and non-Jews. Jews who identified themselves as of Sephardic heritage, from southern Mediterranean ancestry, were nearest genetic neighbors. And Jews who identified themselves as of Ashkenazic heritage, from Eastern Europe, formed another nearest-neighbor group. A study by other researchers published the same month in Nature but with a smaller sample found the same thing.
But those two groups themselves were nearer neighbors, genetically, than they were to their actual geographic neighbors: non-Jewish Italians, for example, or Cypriots or non-Jewish Middle Eastern populations like the Druze. All European Jews seem connected on the order of fourth or fifth cousins, Ostrer says. (More recent work in the HapMap project may have identified this European Jewish signature in North African Jews from places like Morocco and Libya, who also have their own distinct DNA, as well as the European markers.)
“Then people began to use this European data to rewrite history,” Ostrer says. “One thing was that if Ashkenazi and Sephardim were so closely related, there had to be admixture among the populations.” But that isn’t what the genetics was saying. Each group, remember, clustered most closely together. Common DNA markers to both groups were on the next tree branch down. Probably, Ostrer says, the DNA uniting them persisted from a much older split, thousands of years ago, and was not shared between them by more recent intermarriage.
And that makes sense given the cultural history of the two groups, Ostrer says. “There wasn’t that much mobility. They were separated by long distances, and there were language barriers. The Ashkenazi people spoke Yiddish and the Sephardic people spoke Ladino, another language. They weren’t necessarily mutually comprehensible.”
What is more intriguing to scholars, according to Myers, the UCLA historian, is that the two groups are more closely linked to one another than to geographic neighbors. “These people lived in different places for hundreds of years and interacted in different ways with host societies,” he says. “And they saw themselves as different. Actually, both had superiority complexes. Sephardim, for example, thought themselves as very cosmopolitan because of their interactions with the people surrounding them.” They lived in Spain and Portugal in the Middle Ages until they were kicked out during the Inquisition, and they have deeply rooted connections to local culture. The Ashkenazi, on the other hand, had a completely opposite approach to their surroundings. “Ashkenazi felt themselves superior because they resisted interactions. They were not polluted by local influences,” Myers says.
Still, the notion of a shared Jewish biology isn’t going to shock historians, he says. It tracks the historical and cultural traditions of a group that originated in the Middle East and then spread out…