In light of the previous post you know that I was going to post on the new paper in PNAS, North African Jewish and non-Jewish populations form distinctive, orthogonal clusters. Additionally, the press people at Albert Einstein did reach out to me. That doesn’t mean I’ll blog a paper, but it does mean that I’ll give it an extra look. If the authors or people associated with the paper care to have their work publicized, and reach out to humble bloggers, then that’s all good in my book. Also, I suppose over the past two years I’ve become a locus of “Jewnetics” commentary.
In some ways this is the Golden Age of Jewnetics, though we are approaching the epoch of silver. There has to be diminishing marginal returns at some point, and I think the 2010 papers which I reviewed earlier really established the broad outlines of the scientific genealogy of the Jewish people. But just because the broad outlines are established doesn’t mean that there isn’t something to say on specific aspects which haven’t been deeply explored. Some of the commentary on this weblog around the 2010 papers revolved in great deal on the origins of the Jews of North Africa.
The question is simple: how much of the ancestry of the Jews of North Africa derives from the original Jews of antiquity who settled this region, how much derives from indigenous peoples of North Africa, and now much derives from the Sephardic migration out of Iberia ~500 years ago? To recap, one of the major historical processes affecting the Mediterranean Jewry after 1500 was the expansion of a network of Spanish Jews who were expelled from their homeland (unless they converted to Christianity) to the southern and eastern shores of the Mediterranean (with some going to Italy and Western Europe). This resulted in the development of a “Sephardic international,” which was overlain upon an indigenous Jewish substrate which preceded the migrants. So, for example in Greece and Syria there are historically attested differences between the Sephardic Jews who arrived after 1500 and the Jewish communities which preceded them. The same was true of North Africa. But a major complication within this picture is that by and large culturally the Sephardic Jews won. The Sephardic identity superseded and absorbed that of most Jewish communities which had long standing roots in a particular region (e.g., Romaniotes).
In the case of North Africa there are myths which are promoted by some because of legends about Berber tribes which were Judaized. Though there is legitimate academic skepticism about the Jewish identity of Kahina, the Berber queen, it does stand to reason that if the Jewish communities of North Africa date back to Roman antiquity they would possibly have some indigenous ancestry (as well as Latin and Punic). The extent of this ancestry would be a function of the demographic, as opposed to cultural, influence of the Sephardic Jewry.
I was going to review North African Jewish and non-Jewish populations form distinctive, orthogonal clusters at some point soon, but I’m going to have to move that up. Someone on Twitter pointed me to this really weird article, Being Jewish Is More Mind Than Matter: It’s Not Just Genes That Makes Us a People or Nation, by one Robert Pollack. Let me be frank: I have a hard time even commenting on material which I can’t really understand. For example:
Ancestors are a very large population: Each of us can be sure we had more than 1,000 ancestors in only the last 10 generations, or a few centuries. And genetically speaking, a lot can happen over the generations. After all, each of us inherits only one of the two versions of DNA that each parent had previously inherited from his or her parents. A particular version of DNA information may be discarded and lost at any point in time; new DNA may be introduced; or an ancient line of genetic information may be conserved — carried and passed on from generation to generation even as it accumulates different genetic changes that are also passed down.
This stuff is just hard to decrypt. Really it sounds like a high school science paper in portions, but since the author is a professor at Columbia you have to give him more credit than that, and assume he has a deeper meaning, right? Or maybe not.
I know I excoriate readers of this weblog for being stupid, ignorant, or lazy. But this constant badgering does result in genuinely insightful and important comments precisely and carefully stated on occasion. I put up my previous post in haste, and when I published it I wasn’t totally happy with the evidence from which the authors adduced that Ashkenazi Jews were not inbred. Here’s why, from the comments: Doesn’t identity-by-state permutations test reflect a counterbalance of admixture vs. inbredness + drift? Rather than just the degree of inbreeding? Since the population has strong admixture effects, a low IBS doesn’t exclude strong inbreeding, does it?
From my little personal experience IBS is not the best statistic from which to generalize widely, and can be highly misleading in admixed individuals, as implied by the commenter. First, since I’ve stated above that the Ashkenazi Jews are admixed, let me go into a tangent as to why Ashkenazi are admixed between a Middle Eastern and Western European population, as opposed to being a relatively unadmixed ancient Eastern Mediterranean group with affinities to both regions. The previous previous paper found evidence of linkage disequilibrium decay. This means that LD was high in admixed individuals in the past, and declined over time. Why?
Last spring two very thorough papers came out which surveyed the genetic landscape of the Jewish people (my posts, Genetics & the Jews it’s still complicated, Genetics & the Jews). The novelty of the results was due to the fact that the research groups actually looked across the very diverse populations of the Diaspora, from Morocco, Eastern Europe, Ethiopia, to Iran. They constructed a broader framework in which we can understand how these populations came to be, and how they relate to each other. Additionally, they allow us to have more perspective as to the generalizability of medical genetics findings in the area of “Jewish diseases,” which for various reasons usually are actually findings for Ashkenazi Jews (the overwhelming majority of Jews outside of Israel, but only about half of Israeli Jews).
Just as the two aforementioned papers were deep explorations of the genetic history of the Jewish people, and allowed for a systematic understanding of their current relationships, a new paper in PNAS takes a slightly different tack. First, it zooms in on Ashkenazi Jews. The Jews whose ancestors are from the broad swath of Central Europe, and later expanded into Poland-Lithuania and Russia. The descendants of Litvaks, Galicians, and the assimilated Jewish minorities such as the Germans Jews. Second, though constrained to a narrower population set, the researchers put more of an emphasis on the evolutionary parameter of natural selection. Like any population Jews have been impacted by drift, selection, migration (and its variant admixture), and mutation. Teasing apart these disparate parameters may aid in understanding the origin of Jewish diseases.
The paper is open access, so you don’t have to take my interpretation as the last word. Signatures of founder effects, admixture, and selection in the Ashkenazi Jewish population:
At around the same time that the two big Jewish genetics papers came out, there was another one in BMC Genetics which I had overlooked. It’s open access so you can read the whole thing, but seems like they used 32 STR‘s as markers. Their primary finding about Jewish populations was that there was a north vs. south distinction, illustrated in this map:
Update: The main author sent me this email:
Hi, I’m the main author of the paper. Although the map (figure 2 from the paper) does depict differences in the northern vs southern assignment values for a subset of the samples in our study, it does not tell the whole story which might be helped by figure 1. The map figure is based only on subjects who had all 4 grandparents from a single country while the STRUCTURE figures (figure 1) are based on all subjects. There were two main points to the paper. 1. There is a difference, on average, between Ashkenazi and non-Ashkenazi Jewish gene pools and 2. It was only possible to detect this with a small marker panel when hypothetical ancestral or “host” populations were included in the analysis.
In the absence of representative major continental populations, the Ashkenazi and non-Ashkenazi Jewish populations were not distinguishable with the small set of markers. I believe that the dependence of ancestry assignment on which markers and which reference populations are included in an analysis has been mentioned a few times by Razib. This is relevant to the way in which certain gene mapping studies are carried out. For medical genetics studies it is important to know if subjects are from the same population or not; if they are not it can lead to false positive results. Jewish populations are heavily studied in medical research and so we wanted to demonstrate that Jewish populations from different parts of the world should not be lumped together for analysis in medical genetic studies.
Based on published mtDNA and y-chromosome studies as well as historical records we assume that the “”Southern” component of ancestry is Middle Eastern in origin and that differences between Ashkenazi and non-Ashkenazi populations are due to both genetic drift and differences between the populations that contributed to the Jewish gene pools in a given location.
Because I’m a generally somewhat more anthropocentric in regards to my interest in the “squishy science” I am often amused by the wide range of inferences that people make when presented with a set of scientific results. Naturally, when I talk about the genetics of Jews it gets a lot more heated. You did not see most of the extremely bizarre comments which kept coming in as I simply marked them as spam. But I thought I would point to how different individuals can derive totally contradictory inferences from the same posts in two weblog reactions. These two bloggers link to my posts as summaries of the research. First:
…A recent study suggests that Jews are tied by more than common religion, we have the same genetics.
While even some Jews have fought the notion that there is a Jewish race, it is something I am happy to embrace. I am no scientist or geneticist, but it is clearly obvious through recent research that we do, in fact, have a common genetic link. This has been discussed in a second article as well.
While it is complex research, the data speaks for itself. Alan Dershowtiz has said it. Martin Luther King Jr. has said it. And I have said it again and again. If you hate Jews, you do not hate a set of beliefs. You do not hate a country. You are a racist. Period.
I knew Mr. Razib Khan will show his true self eventually, and he did. Despite his protestations to the contrary, he objectively is working for the goal of de-legitimatizing Israel by falsifying scientific data to prove that Jews are not a distinct people with shared identity but a collection of descendants of various South-European ethnic groups. Naturally, this theory is welcomed by various Arab scoundrels with their claim that Israelis are newcomers from Europe, and that Palestinians (Arabs, that is) are closer to original ancestors than “occupiers”-Jews, therefore they have legitimate right to kick Israelis from their homeland and take it for themselves….
After the post on Jewish genetics from a few days ago I was going to do a follow up clarifying a few issues. It was a big paper and I skipped over material which I thought might have benefited from further elaboration, but would have taken up too much time. But Dienekes alerts me to another paper which just came out in Nature of interest, The genome-wide structure of the Jewish people:
Contemporary Jews comprise an aggregate of ethno-religious communities whose worldwide members identify with each other through various shared religious, historical and cultural traditions…Historical evidence suggests common origins in the Middle East, followed by migrations leading to the establishment of communities of Jews in Europe, Africa and Asia, in what is termed the Jewish Diaspora…This complex demographic history imposes special challenges in attempting to address the genetic structure of the Jewish people…Although many genetic studies have shed light on Jewish origins and on diseases prevalent among Jewish communities, including studies focusing on uniparentally and biparentally inherited markers…genome-wide patterns of variation across the vast geographic span of Jewish Diaspora communities and their respective neighbours have yet to be addressed. Here we use high-density bead arrays to genotype individuals from 14 Jewish Diaspora communities and compare these patterns of genome-wide diversity with those from 69 Old World non-Jewish populations, of which 25 have not previously been reported. These samples were carefully chosen to provide comprehensive comparisons between Jewish and non-Jewish populations in the Diaspora, as well as with non-Jewish populations from the Middle East and north Africa. Principal component and structure-like analyses identify previously unrecognized genetic substructure within the Middle East. Most Jewish samples form a remarkably tight subcluster that overlies Druze and Cypriot samples but not samples from other Levantine populations or paired Diaspora host populations. In contrast, Ethiopian Jews (Beta Israel) and Indian Jews (Bene Israel and Cochini) cluster with neighbouring autochthonous populations in Ethiopia and western India, respectively, despite a clear paternal link between the Bene Israel and the Levant. These results cast light on the variegated genetic architecture of the Middle East, and trace the origins of most Jewish Diaspora communities to the Levant.
I doubt it’s a coincidence that this paper came out right on the heels of the previous one; papers are presented at conferences and word gets around, and I assume that the two groups were rushing to get their work published soon enough so as not to be totally overshadowed by the first past the post. The text of both papers is also an interesting window into the role of interpretation in science, as this one seems to emphasize the common Middle Eastern ancestry of Jews (excluding outliers such as the Ethiopian Jews), while the previous one highlighted structure within the Jewish community. Despite the similarities, this second paper is worth exploring for one major reason: it includes two populations of Jews, Moroccans and Yemenis, which were not in the previous research.
The 2,000 year dance between the Jewish people and Western civilization has spawned many questions of scholarly interest. A relatively minor point, though not trivial, has been the issue of the biological relatedness of the Jewish people, and their relatedness to the nations among whom they were resident. This particular point became more starkly relevant with a scientific understanding of human genealogy and genetic relationship in the 18th and especially 19th centuries, but its root can be traced back to antiquity. Jews are not simply a set of individuals who espouse a belief in the God of the Jews, or hold to the laws of the God of the Jews. Rather, one aspect of Jewish identity is its collective component whereby the adherents of the Jewish religion also conceive of themselves as a particular nation or tribe, and therefore bound together by a chain of biological descent. Ergo, the traditional assertion that one is a Jew if one’s mother is a Jew.
Of course these issues can not be understood except in light of a complex historically contingent sequence of events. Our understanding of what it means to be Jewish today, or the understanding of Jews themselves as to their own identity, is the outcome of a long process where self-identified Jews interacted with the broader milieu, as well as evolving in situ. In other words, the Jewish people and the seeds of the Jewish Diaspora were shaped by developments within and without the Jewish culture, and these developments left an impact on the genes of the Jewish people. Contemporary groups outside the “Jewish mainstream,” such as the Beta Israel, Bene Israel and the Karaites, but with an acknowledged connection to Judaism, are windows into other faces of being Jewish besides that of Rabbinical Judaism.
And yet it is descents of the adherents of Rabbinical Judaism, the Judaism of the Pharisees, which we think of when we think of Jews (even the non-Orthodox traditions emerged out of a cultural milieu where Orthodox Judaism was normative). The vast majority of the Jews of the world trace their lineage back to the groups who organized their lives around not just the Bible, but also the Talmud, and subsequently commentaries and rulings by rabbis who were trained in the Talmud. Today these Jews fall into three broad groups, the Ashkenazim, Sephardim and Mizrahim. The Ashkenazim are rather easy to define, as they are the Jews of Central Europe who have been so prominent over the past few centuries. Though it seems likely that in the first millennium their ancestors were to be found along the Rhine, more recently their center of gravity has been in Central & Eastern Europe, in particular Poland and Lithuania. The Sephardim were originally the Jews of Spain, but after their expulsion in 1492 they settled in the Ottoman Empire, and to a lesser extent in other regions of Europe such as the Netherlands. A major confounding issue with the modern Sephardim is that in the Ottoman lands they encountered and interacted with preexistent Jewish communities, who often maintained a distinctive identity subsequent to the influx of the Sephardim. Though in most cases, such as in Morocco and Syria, the Sephardim became culturally dominant and assimilated the indigenous Jewish community into their identity (though they often abandoned Ladino, the language they brought from Spain, for the local lingua franca), in other cases two distinct Jewish communities were coexistent down down to the modern era (e.g. Greece). Finally, the Mizrahim are Jews of the East or Oriental Jews, those Jews whose ancestors hail from Muslim lands where the Sephardim were never a presence. To a great extent the Mizrahim identity is a recent catchall constructed to identify a real dividing line between those groups which are the products of the Sephardic-indigenous synthesis, such as the Moroccan Jews, and those which are not, such as the Yemeni Jews. Often all non-Ashkenazi Jews are referred to as Sephardic because of a common religious liturgy which binds them.