Jacob's Legacy: A Genetic View of Jewish History

Over the past decade the concurrent arrival of relatively cheap sequencing technology as well as copious computational power has resulted a flurry of research in the domain of genetic anthropology with the intent of fleshing out historical questions. Spencer Wells' Journey of Man and Bryan Sykes' The Seven Daughters of Eve were among the early entrants in this burgeoning corpus of popular science literature. Both of these were relatively expansive works, focusing on the deep time histories of the Y and mtDNA lineages, the paternal and maternal ancestry respectively. As the low hanging fruit has been plucked more recent research has focused on narrower and more precise questions. David Goldstein's Jacob's Legacy: A Genetic View of Jewish History is a straightforward but dense exposition of just such a topic. In many ways this is a work which complements Jon Entine's Abraham's Children: Race, Identity, and the DNA of the Chosen People; but while Entine exhibits the narrative flourishes and expansive curiosity of a writer, Goldstein's book is a focused extension of his particular line of research. In fact, there is little scientific content in Jacob's Legacy which couldn't be gleaned from the substantial number of papers which have addressed questions of Jewish genetics over the past 10 years. Of course, I assume that a 120 page book aimed at the popular audience is going to be more intelligible than the discussion sections of two dozen scientific papers.

Goldstein's primary interest in this work is obviously smoking out the fact from the fiction of the history of the Jewish people. To a great extent it is a labor of love driven by personal considerations; as noted in the preface he is a Jew who has developed a greater interest in his cultural background over the years, and most of the original research that he has embarked on in this field were funded through his discretionary monies. The questions posed are relatively straightforward, and despite the author's careful attempt to be subtle and highlight the necessity of nuance, the answers are also rather clear when viewed purely as matters of science as opposed humanity.

Are the priests of the Jewish people, the Cohens, related to each other as implied by their customary paternal descent? Yes, there is a Cohen Modal Haplotype extant at frequencies of 50% among self-identified Cohens, 10% among Jews in general, and less than 1% among non-Jews. Not only does the Cohen Modal Haplotype suggest a connection between the various Cohens of the Diaspora (Ashkenazi, Sephardic, etc.), but it has validated the likely Jewish origin of a black African group in Zimbabwe. What about the Levites, the caste who serve as the aids to the Cohens? It turns out that about half of Levites seem to carry a lineage which is not typically Semitic, but rather is at high frequencies among the peoples of Eastern Europe and Central Asia. Additionally, it seems likely that this lineage entered into the Jewish population about 1,000 years ago. What about the effect of matrilineal descent among most Jewish populations? Goldstein reports some peculiar findings in this area: the short of it is that it seems likely that the first generation of Jews in any given area seem to take local wives, but that subsequent generations are extremely endogamous. The latter reason is why Jews are so distinct from European populations, despite exhibiting all the hallmarks of an admixed population. Distinct genetic histories of the mtDNA and Y chromosomes imply to Goldstein that the Jewish Diaspora pattern has been of mobile males tying together distinct populations, but with women remaining relatively immoble. This results in trends such as the spanning of the Cohen Modal Haplotype across many different Jewish groups (including marginal ones such as the Bene Israel of India), but sharp between population differences when one looks at mtDNA lineages. Goldstein points out that Jewish mtDNA lineages are not only different from each other, but they are very peculiar in a broad Eurasian context so ascertaining their origin is rather difficult (autosomal research which looks at the broader genome seems to suggest admixture with local populations, something one can adduce from the fact that European Jews overlap in appearance with Europeans, and Indian Jews with Indians).

Jacob's Legacy does wander off into broader themes now and then. For example, Goldstein alludes to Lewontin's Fallacy, the misconception that low levels of interpopulation variation on a single locus refutes generalizations of population substructure. Early on there is a reference to the fact that many lay persons and social scientists simply can't comprehend how powerful a tool historical genetics is due to the power of the fallacy. But near the end of the book Goldstein explains that in his own lab he has found that it is rather easy to tell Jews apart from non-Jews based purely on their genetic profile. Not only can we distinguish the continent level origins of individuals, but the granularity has now reached the point of where European population substructure can be spoken of with some confidence.

Finally, near the end of the book there is a foray outside of the domain of historical population genetics into the functional genome; specifically, the relationship between Jewish traits and genetics. When I say traits usually that means disease, as the funding for human genetics usually is grounded in the practical implications it might entail in regards to medical treatment. This section of Jacob's Legacy lacks some focus because it is clear that it is somewhat outside Goldstein's purview, and the external complexities of inferring that gene X results in trait Y for reason Z is something that he is clearly uncomfortable with. Much of the space is given over to geneticists who believe that the existence of "Jewish diseases" (e.g., lysosomal storage disorders, BRCA1, etc.) is a function of genetic drift, sampling variance forced by population size changes over time, especially through bottlenecks and what not, and those who believe that natural selection has reshaped the Jewish genome to give it is peculiar profile. In particular, Goldstein focuses on the area of lysosomal storage diseases and the hypothesis that natural selection for high IQ in heterozygotes explains the high frequency of these disease alleles. Goldstein does not reject the hypothesis, and points out that it is eminently testable, but he seems to express general skepticism. Nevertheless, it is illustrative of the fact that over the next few years differences between populations when it comes to the functional genome will have greater salience, and many more people will have to give greater thought to what that might entail a broader societal framework.

If I had to characterize Jacob's Legacy with a few pithy sentences, I would suggest that in many ways it is a series of discussion sections of scientific papers larded with personal insights which highlight the imporance of interpersonal dynamics in the endeavour of science. The author attempts to describe a few of the technicalities of extracting and sequencing genes, but ultimately it is a superficial enough treatment that that aspect seems pro forma and might best be skimmed. You are told that Mark Thomas is an exceedingly thorough technician and administrator, but you won't be treated to a detailed elucidation of the wet lab methods which resulted in the conclusions which lay at the heart of the book. I don't necessarily think that's a bad thing, you can always find the Methods & Materials section of the papers noted in the biobliography. Jacob's Legacy is ultimatey a Big Think book about a small but interesting topic. Time will tell if the questions and answers that have bubbled up from the exploration of Jewish genetics will serve simply as a trial run for what will come....