The DNA of Abraham’s Children
Analysis of Jewish genomes refutes the Khazar claim. [Excerpts]
Jews have historically considered themselves “people of the book” (am hasefer in Hebrew), referring to sacred tomes, but the phrase is turning out to have an equally powerful, if unintended, meaning: scientists are able to read Jewish genomes like a history book. The latest DNA volume weighs in on the controversial, centuries-old (and now revived in a 2008 book) claim that European Jews are all the descendants of Khazars, a Turkic group of the north Caucasus who converted to Judaism in the late eighth and early ninth century. The DNA has spoken: no.
In the wake of studies in the 1990s that supported biblically based notions of a priestly caste descended from Aaron, brother of Moses, an ambitious new project to analyze genomes collected from Jewish volunteers has yielded its first discoveries. In a paper with the kind of catchy title you rarely see in science journals—“Abraham’s Children in the Genome Era”—scientists report that the Jews of the Diaspora share a set of telltale genetic markers, supporting the traditional belief that Jews scattered around the world have a common ancestry. But various Diaspora populations have their own distinct genetic signatures, shedding light on their origins and history. In addition to the age-old question of whether Jews are simply people who share a religion or are a distinct population, the scientific verdict is settling on the latter.
Although the origin of the Jews has been traced, archeologically, to the Middle East in the second millennium B.C.E., what happened next has been more opaque. To sort it out, researchers collected DNA from Iranian, Iraqi, Syrian, and Ashkenazi Jews around New York City; Turkish Sephardic Jews in Seattle; Greek Sephardic Jews in Thessaloniki and Athens; and Italian Jews in Rome as part of the Jewish HapMap Project. (All four grandparents of each participant had to have come from the same community.) As the scientists will report in the next issue of the American Journal of Human Genetics, the analysis shows that “each of the Jewish populations formed its own distinctive cluster, indicating the shared ancestry and relative genetic isolation of the members of each of those groups.”
Jewish populations, that is, have retained their genetic coherence just as they have retained their cultural and religious traditions, despite migrations from the Middle East into Europe, North Africa, and beyond over the centuries, says geneticist Harry Ostrer of NYU Langone Medical Center, who led the study. Each Diaspora group has distinctive genetic features “representative of each group’s genetic history,” he says, but each also “shares a set of common genetic threads” dating back to their common origin in the Middle East. “Each of the Jewish populations formed its own distinctive cluster, indicating the shared ancestry and relative genetic isolation of the members of each of those groups.”
The various Jewish groups were more related to each other than to non-Jews, as well. Within every Jewish group, individuals shared as much of their genome as two fourth or fifth cousins, with Italian, Syrian, Iranian, and Iraqi Jews the most inbred, in the sense that they married within the small, close-knit community. In general, the genetic similarity of any two groups was larger the closer they lived to one another, but there was an exception: Turkish and Italian Jews were most closely related genetically, but are quite separated geographically.
The DNA analysis undermines the claim that most of today’s Jews, particularly the Ashkenazi, are the direct lineal descendants of converted Khazars—which has angered many in the Jewish community as an implicit attack on the Jews’ claim to the land of Israel, since it implies that today’s Jews have no blood ties to the original Jews of the Middle East. Instead, find the scientists, at most there was “limited admixture with local populations, including Khazars and Slavs ... during the 1,000-year (second millennium) history of the European Jews.”
Analysis of Jewish genomes has been yielding fascinating findings for more than a decade. A pioneer in this field, Michael Hammer of the University of Arizona, made the first big splash when he discovered that genetics supports the biblical account of a priestly family, the Cohanim, descended from Aaron, the brother of Moses: one specific genetic marker on the Y chromosome (which is passed on from father to son, as membership in the priestly family would be) is found in 98.5 percent of people who self-identify as Cohanim, he and colleagues reported in a 1997 paper in Nature (the PBS science series Nova did a nice segment on that work, summarized here). The Cohanim DNA has been found in both Ashkenazi and Sephardic Jews, evidence that it predates the time when the two groups diverged, about 1,000 years ago. DNA can also be used to infer when particular genetic markers appeared, and suggests that the Cohanim emerged about 106 generations ago, making it fall during what is thought to be the period of the exodus from Egypt, and thus Aaron’s lifetime.
(Begley, “The DNA of Abraham’s Children,” Newsweek Online, June 3, 2010).