According to search engine traffic one of the most popular posts on this weblog has to do with the genetic background of Ashkenazi Jews. That is, those Jews whose ancestors derive from Central & Eastern Europe, and the overwhelming number of Jews in the United States. The genetic origins of this group are fraught with politics naturally. With the rise of biological science the characteristics of Jews were used as a way to differentiate them as a nation apart in more than a cultural and religious sense. After World War II other researchers attempted to show that Jews were not genetically distinct with relatively primitive blood group assays. Rather, they were the descendants of converts. More recent genetic work has given mixed results. The reasonable inference then is that Jews themselves are a population with a complex history, and that complexity is manifest in their genetics. A new paper explores these issue in more detail, Genomic microsatellites identify shared Jewish ancestry intermediate between Middle Eastern and European populations:
Background Genetic studies have often produced conflicting results on the question of whether distant Jewish populations in different geographic locations share greater genetic similarity to each other or instead, to nearby non-Jewish populations. We perform a genome-wide population-genetic study of Jewish populations, analyzing 678 autosomal microsatellite loci in 78 individuals from four Jewish groups together with similar data on 321 individuals from 12 non-Jewish Middle Eastern and European populations. Results We find that the Jewish populations show a high level of genetic similarity to each other, clustering together in several types of analysis of population structure. Further, Bayesian clustering, neighbor-joining trees, and multidimensional scaling place the Jewish populations as intermediate between the non-Jewish Middle Eastern and European populations. Conclusion These results support the view that the Jewish populations largely share a common Middle Eastern ancestry and that over their history they have undergone varying degrees of admixture with non-Jewish populations of European descent.
The general results of the paper are well illustrated by the figures. The figure below shows the putative ancestry of individuals assuming a K number of ancestral populations. As you can see, the Jews within the sample are placed between Middle Eastern and European groups. At K = 5 and K = 6 the relationship between Jews and Palestinians shows up; a common ancestral population which parted aways at some point.
And here's a neighbor-joining tree. The Jewish groups in red, Europeans in blue and Middle Eastern groups in olive.
Now here are Jews compared to various populations. Jews are in red. I've reedited and labelled for clarity.
From the conclusion of the paper:
A simple explanation for the clustering of the Jewish populations is that this pattern is the consequence of shared ancestry with an ancestral Middle Eastern group. Under this scenario, the intermediate placement of the Jewish populations with respect to European and Middle Eastern populations would then result from early shared ancestry of the Jewish and Middle Eastern populations, followed by subsequent admixture of the Jewish populations that took place with European groups or other groups more similar to the Europeans than to the Middle Eastern populations in the study. Although it is difficult to assess the specific nature of the admixture on the basis of our analysis, this explanation is supported by other genetic studies that find a combination of shared ancestry and admixture among Jewish populations...and by historical records of conversions to Judaism...Further sampling of matched Jewish and neighboring non-Jewish populations will be informative for investigating the evidence for this scenario. ... In several analyses, the population in the study that is most similar to the Jewish populations is the Palestinian population. This result is reflected by the fact that for K=5, Bayesian clustering with Structure assigns the Jewish populations and the Palestinians to the same cluster...and by the relatively close placement of the Palestinians and the Jewish populations in MDS plots of individual distances...This genetic similarity, which is supported by several previous studies...is compatible with a similar Middle Eastern origin of the Jewish populations and the Palestinians. Admixture of the Palestinians with groups with European origins might have maintained or augmented this shared ancestry, especially if it was paralleled with similar admixture of these groups with Jewish populations. ... We note that caution is warranted in interpreting some of our results. For example, in the population trees produced from three distance measures...there is disagreement on the branching order of three of the European populations closest to the Jewish populations (Adygei, Sardinian, and Tuscan). Thus, from these data, it is difficult to make strong inferences regarding the most similar European populations to Jewish groups. However, consistent with studies that have incorporated a single Jewish population in a broader European context...southern groups from Europe are placed closer to the Jewish populations than more northerly groups.
This paper clarifies and puts into sharper focus what we knew, and leaves open more details for future research. 1) Jewish populations do have a common ancestral affinity. 2) But, that affinity is complemented by admixture with the populations amongst whom the Diaspora settled. 3) There is a suggestion that in the case of Ashkenazi Jews the European contribution was more likely to be from southern, and not northern, Europe. This is somewhat surprising in light of the fact that the Ashkenazi group crystallized during the medieval period in northern Europe, amongst German and Slavic speaking peoples. These data would imply that in fact there was a relatively strong separation between these groups and the Jews, at least when it came to gene flow into the Jewish group (other data from Poland does show the effect of Jewish assimilation into the gentile majority). Therefore, the admixture may have occurred within the bounds of the former Roman Empire, during the Imperial or early post-Imperial period. 4) The close relationship of Jews to Palestinians is not surprising. Jews are reputedly a Levantine population by origin, and the historical and genetic evidence points to Arabicization in the Levant and Mesopotamia as having occurred through acculturation, and not population replacement. Many of the Palestinians are likely of original Jewish or Samaritan origin, though I would guess that they were likely at least nominally Christianized during the Byzantine persecutions of the 6th century. 5) There remain questions as to which groups the Ashkenazi Jews admixed with, and when they admixed. There should be a different pattern of genetic variance if the admixture event was early and ceased, or if it was constant and gradual gene flow. The phylogenetics implies the former, because of the lack of much allele sharing with northern Europeans specifically, amongst whom the Ashkenazi Jews were resident for the past ~1,000 years. Within the text of the paper there are also hints of possible relationships to a population of the Caucasus, opening an avenue for some validity of the Khazar hypothesis. There have been other data which also point to the Khazar hypothesis. The origins of the Jews then likely are complex. Many of the confusions and muddled points will likely be clarified soon with more data and analysis. At Dienekes' some observed that a greater number of Mediterranean populations would have been useful. What if the Jewish admixture event tended to occur with Greeks in Alexandria and in the cities of Asia Minor? That would explain the proximity to Italians, but lack of overlap with other European groups. Citation: BMC Genetics 2009, 10:80 doi:10.1186/1471-2156-10-80 (H/T Dienekes)