By Diana Muir Appelbaum, Paul S. Appelbaum

“Studies Show Jews’ Genetic Similarity,” announced a recent headline in the New York Times. The two studies in question, each involving an international team of researchers, reported the results of genome-wide analyses of a variety of Jewish and non-Jewish population groups from around the world. Despite using different samples and analytic techniques, the overall findings of the two groups were quite similar: almost all of the Jewish groups clustered fairly tightly on maps of genetic variation, overlapping considerably with some Middle Eastern groups (e.g., Druse and Cypriots), but showing much less consanguinity with populations from their host countries. The fact that these studies were reported in America’s newspaper of record suggests significance beyond whatever scientific value the findings may have. What is that significance?

For observers who have followed the recent work on genetics of the Jews, the findings of the newer studies were not surprising. Previous research looking at markers of paternal lineage on the Y chromosome and maternal descent in mitochondrial DNA yielded similar results. The earlier studies had also turned up some less expected findings. Paternal Y chromosome markers among the Bene Israel Jews of India showed markers characteristic of other Jewish populations, but maternal mitochondrial markers were similar to those found in populations on the subcontinent. Ethiopian Jews are more similar genetically to other sub-Saharan African groups than to other Jews. And many Jewish populations appear to have had only a small number of maternal founders: one study demonstrated that 27% of Moroccan, 41.3% of Bene Israel and 51.4% of Georgian Jews are descended from a single female ancestor in each community.

The question remains, however, what difference these data make. Perhaps the clearest answer relates to our understanding of Jewish history and the migration patterns of the Jews. Almost all Jewish groups (Ethiopian Jews being the major exception) show evidence of common descent from a Middle Eastern population, with major branch points corresponding to known historical events. Using techniques that estimate the time-course of divergence among populations, one of the recent studies, for example, estimated that Persian and Iraqi Jews separated from other Jewish groups about 2500 years ago—a period corresponding to the conquest of Judea by Nebuchadnezzar’s army and the transfer of a significant proportion of the population to exile in Babylon. In this case, the genetic data confirm the traditional view of the origin of these communities.

Other instances illustrate the potential of genetic studies to shed new light on historical understandings. Many scholars had assumed that far-flung Jewish communities were established by merchants who settled in distant lands and took local wives. In some cases, such as the Bene Israel of India, this narrative appears to be confirmed by mitochondrial DNA analyses. However, ancient Jewish women were more intrepid than historians thought. A study of the mitochondrial DNA of Ashkenazi (i.e., northern and central European) Jewish women reported that close to half (42%) were descended from one of just four matriarchs with distinctive haplotypes that most probably originated in the Levant. Thus, it appears that the male founders of remote Jewish communities did not rely exclusively on marriage with local women, but were sometimes accompanied by their wives or sent home for brides.

Genetic data have also been useful for debunking myths of Jewish history. The best example is the Khazar hypothesis, popularized (though not originated) by the critic and novelist Arthur Koestler in the mid-twentieth century. A people of the central Asian steppes, the Khazars founded a major kingdom north of the Caspian Sea in the seventh century, and between one and two hundred years later Khazar leaders and some undetermined proportion of the people converted to Judaism. After the 10th century, they disappeared from history. Koestler promoted the idea that Ashkenazi Jewry was largely descended from the Khazars, who he speculated had migrated into central Europe. Although the genetic data cannot exclude some introjection of Khazar genes into Ashkenazi gene pool—and there are even some data consistent with this possibility—it seems clear that this constitutes at most a minor contribution to Ashkenazi ancestry. Koestler’s literary skills notwithstanding, the Jewish populations of European origins have clear Levantine roots.

More broadly, widespread assumptions that since Ashkenazi Jews are usually pale while Near Eastern Jews tend to be swarthy, the latter must be much more closely related to the peoples among whom their ancestors lived have been overturned. As would be expected from their appearance, Ashkenazi Jews have a higher admixture of European genes than do their Mizrachi cousins, but in both groups the genetic links to Levantine ancestry is strong.

Where genetic data have not been helpful—not surprisingly—have been at the individual and geopolitical levels. Whether Jewish identity is defined from a religious or ethno-national perspective, genetics have little to offer to the question of “Is this person a Jew?” The traditional religious view of Jewish identity is that a Jew is a person who was born to a Jewish mother or had a conversion according to Jewish law. (Reform Jews expanded the definition in the 1980s to include patrilineal descent.) Regardless of a person’s genetic makeup, that remains true today. Indeed, the substantial percentages of genetic overlap between Jews and the host populations of their countries of long-term residence, as well as reports of mass conversions in the Hasmonean and Roman periods, suggest that in-migration of non-Jews to the Jewish religious community is not a recent phenomenon. Thus, although Jews as a group bear a certain genetic distinctiveness compared with most other population groups, on an individual basis genetics are useless in determining religious identity.

A similar conclusion applies to what is probably the most highly publicized of the findings regarding the genetics of the Jews, namely the "Kohen modal haplotype." The Kohanim (plural form) are the hereditary Jewish priests, who had extensive ritual responsibilities before the destruction of the Temple in Jerusalem by the Romans, and who have retained some residual, if less crucial, ceremonial duties (and some behavioral restrictions under Jewish law) since. As described in the Book of Exodus, the priestly role was awarded to Moses’ brother Aaron and his male descendants after him. In the 1990s, it occurred to an Israeli geneticist, himself a Kohen, that if the biblical story were accurate and if the tradition of kohanic descent had been reliably conveyed in the years since—both accounts having no shortage of skeptics— Kohanim should share common markers on their Y chromosomes. To the surprise of many people, such a haplotype, comprising 6 markers, was found in 45-61% of Ashkenazi Kohanim, 56%-69% of Sephardi Kohanim, and 10%-15% of other male Jews. (Subsequent work applying a narrower definition of the haplotype, requiring the presence of additional markers, lowered the percentages somewhat.8) However, one’s status as a Kohen according to Jewish law remains dependent on the possession of a family tradition: the presence of the Kohen modal haplotype does not confer priesthood on someone without such a tradition and its absence does not deprive a Kohen of that status. Once more, genetic data’s historical value does not transfer to the level of individual identity.

Nor is the conclusion different in the ethno-national realm. Groups with longstanding identification with the Jewish people, generally including some degree of observance of traditional Jewish practices, have been accepted as Jews regardless of genetic findings. As early as the 16th century, for example, the black Jews of Ethiopia were recognized by major religious authorities as authentic Jews, despite their lack of physical resemblance to other Jewish populations. By the late 20th century, as noted, data were suggesting that genetic markers among Ethiopian Jews were unlike those of other Jewish groups, and much closer to surrounding African populations. These data, however, have been essentially irrelevant to the view that the Beta Israel, as they call themselves, are part of the Jewish people, and to the decision of the State of Israel to grant them citizenship.

At the geopolitical level, namely the struggle between Israelis and Palestinians over ownership of all or part of the land between the Jordan River and the Mediterranean, the impact of the genetic findings has not gotten much further—nor should it— although it may have precluded the introduction of some irrelevancies into the debate. Assertions that since Ashkenazi Jews are descendants of the Khazars they have no claim in the Middle East have now, thankfully, been put aside in the face of disconfirmatory genetic data. But all the national groups that have looked to genetics to support their claims to sovereignty over a particular land, as we have suggested elsewhere,ix are bound to be disappointed. Such arguments are usually made on the basis of one group having a closer genetic connection to the original inhabitants of the land than a competing population, socalled "historical primacy." Not only are such questions of historical relatedness difficult—and in many cases impossible—to resolve, but such chronological primacy is only one component that usually gets taken into account in determining who has the right to live in or control a land. Self-determination, corrective justice, efficient land use, and attachment to a territory are other factors that enter into these difficult assessments. Genetics has not and will not solve the conundrum in the Middle East.

Taken as a whole, the genetic studies of varied Jewish populations around the world illustrate the ability of modern laboratory techniques to contribute to a better understanding of historical phenomena, particularly when they involve the movement of populations. However, Jewishness is not a genetic trait, never was, and never will be.

Diana Muir Appelbaum is a historian who is working on a book on nationalism. Paul S. Appelbaum, MD is the Dollard Professor of Psychiatry, Medicine and Law at Columbia,where he heads a center studying ethical, legal and social implications of findings in genetics. Together they have written for a variety of publications on the significance of genetics for national and individual identity.


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