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The Genealogical ScienceThe Search for Jewish Origins and the Politics of Epistemology
By NADIA ABU EL-HAJ
The University of Chicago PressCopyright © 2012 The University of Chicago
All right reserved.
Chapter OneThe Descent of Men
In an unusual marriage of science and religion, researchers have found biological evidence in support of an ancient belief: certain Jewish men, thought to be descendants of the first high priest, Aaron, the older brother of Moses, share distinctive genetic traits, suggesting that they may indeed be members of a single lineage that has endured for thousands of years. —(Grady 1997b)
In an article in the New York Times, speaking of the publication in Nature of the first Y-chromosome study of the Jewish priesthood (the Cohanim), Michael Hammer described the results as a "beautiful example of how father-to-son transmission of two things, one genetic and one cultural, gives you the same picture" (Grady 1997b). The author of the article, Denise Grady, wrote in a subsequent article in the Times that something (scientifically) new is happening here:
Until now, the appeal and the fear of genetic testing have stemmed from its ability to predict the future. Will a baby be born with Down syndrome? Will a neurological disease or cancer strike a person down in the prime of life? While these tests have provided a window on the future and maybe even a way of avoiding tragedy, not everyone has wanted to know what they reveal. This month, though, researchers described a novel use of a genetic test—to look deep into the past—and people are clamoring to know more. (Grady 1997a)
In this chapter, I analyze research projects on the origins of contemporary Jews in order to illuminate more generally the forms of evidence that anthropological geneticists use to map group-based diversity, to construct population phylogenies, and to determine the "origins" of specific groups. More specifically, I examine Y-chromosome research, which, by the turn of the millennium, many anthropological geneticists considered one of the most reliable kinds of phylogenetic data. I draw upon my research on genetic studies of the origins and kinship of contemporary Jewish communities in order to sketch the broadest contours of the grammar—scientific, ethical, and political—of the science of anthropological genetics.
Critics have argued that anthropological genetics, or the study of population-based genetic diversity, is but the latest heir to race science, a scientific project begun in the nineteenth century that defined the human species in the language of biological kinds and delimited absolute categories of human difference (Duster 1998; Palmié 2007; Stevens 2002). What I argue in this chapter, however, is that despite apparent continuities in classificatory practices, anthropological genetics' relationship with race science is not so seamless. I highlight evidentiary logics other than practices of classification (the persistence of categories) and I ask, what exactly is being "discovered" through the identification of molecular differences? What are these biological markers of difference taken to be signs of? In developing my argument, I focus on the relationship between nature and culture presumed in population-specific genetic historical work.
Anthropological genetics divides humanity up into its "constituent parts"—its ethnic, linguistic, and racial groupings. In so doing, however, it does not produce the same understandings of human groups or of human difference as did race science. In what follows, I examine what makes a population legible and meaningful in anthropological genetics. I consider the political significance of the field's epistemological assumptions, evidentiary practices, working objects, and historical arguments. In so doing, I explore why it might be that genetic historical quests—as population-based research and as individual genetic-ancestry tests—are widely embraced today.
"According to biblical accounts, the Jewish priesthood was established about 3,300 years ago with the appointment of the first Israelite high priest. Designation of Jewish males to the male priesthood continues to this day, and is determined by strict patrilineal descent," explain Karl Skorecki and Michael Hammer in their first published paper on Y-chromosome research into Jewish origins (Skorecki et al. 1997, 32). If priestly descent (the Cohen lineage) has been passed from father to son originating with the biblical figure of Aaron, the paper reasoned, it should be possible to find evidence consistent with the biblical account through genetic analysis. A nephrologist at the Ramban Medical Center at Haifa's Technion, Skorecki contacted Michael Hammer at the University of Arizona because of Hammer's expertise in using the Y-chromosome to trace population origins.
As Karl Skorecki tells the story, the inspiration for this research was born of a whim: he was sitting in synagogue one day and a man—a Cohen from North Africa—stood up to perform his duties. Skorecki wondered what the two of them, both Cohanim but from vastly different regions of the world, might share. If the story of priestly descent were true, their common origins should be visible on the Y-chromosome. He started research into the Y-chromosome of Jewish priests as a hobby of sorts through which he would, ultimately, join forces with other researchers in an effort to expand Y-chromosome studies of Jewish history (see the PBS program, The Lost Tribes of Israel ).
Skorecki and Hammer collected DNA samples from 188 Israeli, British, and North American Jewish men. They compared the Y-chromosomes of Jewish men who self-identified as Cohanim (n = 68) with men who self-identified as either Levites (a second priestly line) or as "lay-Jews," who were named in the study, in accordance with biblical tradition, "Israelites." If the biblical and oral traditions of priestly origins and descent are historically accurate, "observable" differences should exist between the Y-chromosome haplotypes of "Jewish priests and their lay-counterparts" (Skorecki et al. 1997, 32).
The 1997 Nature paper announced just such an observable difference. Excluding Levites from the final analysis (Levites exhibited no pattern of patrilineal descent from a single ancestor), Hammer and Skorecki compared Cohanim and Israelites. On the basis of polymorphisms at two genetic loci, Skorecki concluded that there is a difference in the Y-chromosome haplotypes of priests versus lay Jews, thus "confirm[ing] a distinct paternal genealogy for Jewish priests" (1997, 32). To further explore the results, Skorecki and Hammer, joined by colleagues at University College London who would emerge as central figures in studies of Jewish genetic history, designed a more expansive study, the results of which were published in a paper in Nature in 1998 (Thomas et al. 1998). An examination of the Y-chromosomes of 306 Jewish men and based upon a haplotype constructed out of twelve genetic loci, this second study generated similar results. (A haplotype is a set of genetic markers on a given chromosome that are inherited together, or "linked.") "Despite extensive diversity among Israelites," the authors argue, "a single haplotype ([now named] the Cohen Modal Haplotype) is strikingly frequent in both Ashkenazi and Sephardi Cohanim" (Thomas et al. 1998, 138, emphasis added). The Cohen modal haplotype, the most common haplotype found in Cohen men, is present in approximately 50 percent of Cohanim (0.449 of the Ashkenazi Cohen sample, and 0.561 of the Sephardi Cohen sample) (Thomas et al. 1998). "Given the relative isolation of Ashkenazic and Sephardic communities over the past 500 years, the presence of the same modal haplotype in the Cohanim of both communities strongly suggests a common origin" (ibid., 139).
Delineating descent is but one aspect of these projects of historical reconstruction. The question of time is at least as important: "To the extent that patrilineal inheritance has been followed since sometime around the Temple period (roughly 3,000-2,000 years before present), Y chromosomes of present day Cohanim ... should derive from a common ancestral type no more recently than the Temple period" (Thomas et al. 1998, 138). In other words, the "coalescence time" (the time of origin) of the Cohen modal haplotype must date to before the "dispersion of the priesthood following the Temple's destruction" (138).
Estimating coalescence time is a complex process. At a bare minimum, it depends on knowing the "normal" rate of mutations in the Y-chromosome, specifying what is referred to as the "molecular clock." In addition, it requires assuming the time of a generation—15, 20, 25, or 30 years. In the 1998 Nature paper, the researchers determined that the Cohen modal haplotype originated approximately 106 generations ago. Multiplying that number by 25 (or 30) years, they concluded that the Cohen modal haplotype dates to 2,650 (3,180) years before present. The authors state that, "ignoring uncertainty in the mutation rate," there is a 95 percent confidence interval that the coalescence time of the Cohen modal haplotype is 2,100–3,250 years before present, "sometime during or shortly before the Temple period in Jewish history" (1998, 139).
The conclusions of the 1998 paper went much farther than that, however. Might the Cohen modal haplotype indicate more than just priestly descent?
The identification of haplotypes with restricted distributions may provide "signatures" of ancient connections that have been partially obscured by subsequent mixing with other populations. Gene flow from the Cohanim could account for the presence of the Cohen modal haplotype in both Ashkenazic and Sephardic Israelites, or it could be a signature of the ancient Hebrew population. The Cohen modal haplotype may therefore be useful for testing hypotheses regarding the relationship between specific contemporary communities and the ancient Hebrew population. (Thomas et al. 1998, 139, emphasis added)
While not definitive, the authors think that the Cohen modal haplotype—found in approximately 10 percent of Ashkenazi and Sephardic "Israelites" —may well indicate ancient Hebrew and not just priestly origins. Having discovered a possible indicator of common Hebrew ancestry, the opportunity to use genetic information to study the patrilineal origins and descent of contemporary Jewish communities was opened up. Further examinations of Jewish origins would rely, at least initially, on the Cohen modal haplotype—determining its geographic origin, using it as a normative measure of ancient Hebrew descent. Researchers turned to the Cohen modal haplotype and to a search for other Y-chromosome types shared or "prevalent" in contemporary Jewish populations in order to evaluate the historical relatedness of contemporary Jewish communities, the veracity of the history of the Jewish people as a history of diaspora born out of exile from ancient Palestine, and the claims of "potential" Jews, groups of Jews who believe they are descendants of ancient Israel.
In Search of Population Histories
The turn to DNA to pursue a "curiosity about origins" is not new, as two prominent researchers in anthropological genetics explain. DNA "has been passed down to us from our ancestors, accumulating mutations along the way." As such, "the DNA of modern humans are ... different from each other, and these differences, or polymorphisms, provide a record of our relatedness and genetic history" (Jobling and Tyler Smith 1995, 445). And as records of our relatedness, two loci are believed by most, though not all, anthropological geneticists to provide the most useful data: mitochondrial DNA and the Y-chromosome.
Mitochondrial DNA and the Y-chromosome are passed down unilineally. One inherits one's mtDNA from one's mother. Men inherit their Y-chromosome from their fathers. As explained by Jobling and Tyler-Smith, "Neither of these segments of DNA recombines at meiosis, and this means that they each contain a particularly simple record of their past" (1995, 449). As a result, the biological principles of descent are pried apart: one can track one's lineage via the maternal or the paternal line. The two lines remain fully independent of one another, and the "history" of each is distinct. By deciphering the sequence of nucleotides (the order of the chemical components of DNA), anthropological geneticists reconstruct population histories by delineating lines of descent believed to be archived in the history of genetic polymorphisms (a variation or mutation in the sequence of nucleotides among individuals) as they are passed down from mothers to their children and from fathers to their sons.
Mitochondrial DNA was used in anthropological genetic studies long before the Y-chromosome (I discuss mtDNA–based phylogenetic research in chapter 3). The use of the Y-chromosome is actually relatively new. Jobling wrote in a paper published in 1994, "The human Y chromosome is poor in conventional DNA polymorphisms," hindering "studies of the paternal lineage" (1994, 107). For the Y-chromosome to be useful to phylogenetic analysis, sufficient genetic diversity must be present in human Y-chromosomes—and it was not until the late 1990s that a sufficient amount of diversity was found.
Anthropological genetics explores the history of human migrations and population-specific origins and relatedness by analyzing diversity at the molecular level. (By way of contrast, for example, population genetics in the 1950s and 1960s analyzed the phenotypic diversity evident in blood group distributions without any knowledge of the specific genotypes [see chapter 2]). Using genetic data to make inferences about population histories involves starting with the principle that, under certain circumstances and assumptions, "genetic similarity reflects common ancestry" (Relethford 2001, 68). But genetic similarity is derived from an analysis of polymorphisms, of genetic differences. As articulated by John Relethford, a paradox stands at the heart of genetics and evolutionary theory. Consider the case of mtDNA and the search for "Eve," the female (genetic) ancestor of all modern humans. If we all trace back to a single ancestor, must not our DNA—in this instance, our mtDNA—be identical? If so, how can we use mtDNA to untangle the different genetic relationships or degrees of relatedness among individuals—or among groups?
Descent from a common ancestor does not imply identity. Rather, it implies a presumably decipherable matrix of genealogical relationships "visible" in genetic polymorphisms. According to current scientific understandings of evolution, as organisms reproduce, molecular mutations are generated randomly: some are deleterious, some positive, and most are neutral. Researchers decipher (the chain of) those presumably step-wise (one mutation at a time) mutations in order to reconstruct genealogies, using genetic differences among pairs of individuals to evaluate their kinship: "the greater the length of time separating two individuals, the more mutations will accumulate, and the greater the genetic difference between them" (Relethford 2001, 72). At its simplest, that is the underlying assumption of phylogenetic analysis. Genetic distance is a measure of the relationship of one population to another: the more genetically similar, the more recently two populations had a common ancestor, the more genetically dissimilar, the more remote the common ancestor. By identifying specific polymorphisms on the basis of which distinct haplotypes (sets of linked polymorphisms on a given chromosome) are constructed, one individual or group of individuals is compared to another. With respect to studies of Jewish priestly origins, scientists ask: What is the relative frequency of the Cohen modal haplotype in Jewish priests versus lay Jews? What is the relative frequency of the Cohen modal haplotype in Jewish versus non-Jewish populations? What is the origin of the Cohen modal haplotype? In what other populations does one find either the same haplotype or a haplotype closely "related" to it (by being a few mutations removed)? And what might all this information tell us about the geographic origins of today's Jews?
Diversity has long played a central role in biological thought (Mayr 1982). From eighteenth- through twentieth-century biology, as Jenny Reardon has written, diversity has been a "key object" of speculation and research (2001, 361). "Is the diversity of the natural world meaningful? What is the appropriate unit of analysis" (361)? Moreover, "Where does diversity come from? Individuals or groups? If groups, how should these groups be defined, by whom and for what purposes" (358)? In the eighteenth century, Carl Linnaeus first codified and mapped biological diversity "by describing kinds of organisms in the terms of a strictly imposed formal system borrowed from classical logic" (Hey 2001, 7). He understood classes of organisms (genus, species) to be made of "distinct and unchangeable kinds of organisms that had been created by God" (8). Linnaeus's system for classifying organisms was typological in character, what Jody Hey has called a "well-codified version of Platonic and Aristotelian essentialism" (8).
In the late nineteenth century Darwin recast both the meaning and the significance of diversity. "The living world became a world in time, and both its occupants and its relational structure were refigured as products of its evolutionary history" (Keller 2000, 7). In contrast to Linnaeus, Darwin described "a continuum of variation—individual differences, to varieties, to species" (Hey 2001, 8). Darwin's evolutionary theory provided a mechanism through which the origin and transformation of species would be understood—natural selection acting upon individual variation. And in its emphasis on transformation and not just "origin," Darwin's theory of evolution paved the way for "a comparison of organisms not only in space but in time," which became the hallmark of modern genetics (Gudding 1996, 529). And as narrated retrospectively, Darwin's shift of emphasis to individual variation laid the groundwork for biological and anthropological projects to come. The race concept was deconstructed on the basis of arguments that most genetic variation occurs at the level of individuals and not between so-called racial groups. Moreover, group-level differences came to be understood to be, by and large, biologically insignificant.
Excerpted from The Genealogical Science by NADIA ABU EL-HAJ Copyright © 2012 by The University of Chicago. Excerpted by permission of The University of Chicago Press. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Table of ContentsContents Acknowledgments Introduction One / The Descent of Men Two / What Are the Jews? Three / Know Thyself Four / The Politics of Identity, Inc. Five / The Right of Return Six / The Things We Carry: History through the Molecular Optic References Notes Index
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