Contemporary Jews are an aggregate of ethno-religious communities whose world-wide members identify with each other through shared religious, historical and cultural traditions. It is only recently that the genetic structure of the Jewish people has been addressed and elucidated using gene-array technology.
Nature in 1998(1) published an article entitled “Origins of Old Testament Priests” in which the authors examined the hypothesis that the Y chromosomes of present-day Cohanim and Leviim should be distinguishable from those of other Jews and derive from a common ancestral type no more recently than the Temple period. The authors also showed that although the Levite chromosomes are diverse, Cohen chromosomes are homogenous. 306 male Jews from Israel, Canada and the UK were involved in the study.
The methodology of this study, which is explained in detail in the paper, includes an estimation of time since the chromosomes were derived from the ancestral chromosome. The estimate is 106 generations, which for a generation time of 25 (30) years gives an estimate of 2,650 (3,180) years, dating the coalescence of the Cohanim chromosomes to between the Exodus and the destruction of the first Temple (586 BCE).
“The genome-wide structure of the Jewish people” by Doron Behar et al (2) reports on a study which compares genotypes of individuals from 14 Diaspora Jewish communities with individuals from adjacent non-Jewish communities and with individuals from non-Jewish populations from the Middle East and North Africa. Most Jewish samples clustered with Druze and Cypriot samples but not from other Levantine or paired Diaspora host populations. Indian and Ethiopian Jews clustered with their local host populations and the Bene Israel also showed a clear paternal link to the Levant.
The best explanation for these findings is a common genetic origin consistent with the historical formulation of the Jewish people as descending from ancient Hebrew and Israelite residents of the Levant. There is significant genetic continuity among most Jewish communities and contemporary non-Jewish Levantine populations despite their long-term residence in diverse regions remote from the Levant and isolation from one another. In addition, most Jewish samples could be partitioned into Ashkenazi-north African-Sephardi, Caucasus-Middle Eastern and Yemenite subclusters.
In the paper “Abraham’s Children in the Genome Era…” by Gil Atzmon et al (3), the authors describe a genome-wide analysis and comparison with local populations for representatives of 3 major groups of the Jewish Diaspora; Eastern European Ashkenazim, Italian, Greek and Turkish Sephardim, and Iranian, Iraqi and Syrian Mizrahim. Data were generated from 237 unrelated individuals (51% female) from the 7 Jewish populations which were merged with selected data sets from the Human Genome Diversity Panel.
In this study, the most distant and differentiated of the Jewish populations were Iranian Jews followed by Iraqi Jews. Two major groups were identifiable that could be characterised as middle-eastern (Iranian and Iraqi) and European/Syrian Jews. The Druze, Palestinian, and Bedouin were on branches distinctive from the other populations. The Italian, Syrian, Iranian, and Iraqi Jews demonstrated the high levels of IBD(identity by descent) that would be expected for extremely inbred populations.
In this study, Jewish populations from the 3 major Jewish Diaspora groups, Ashkenazi, Sephardi and Mizrahi, formed a distinctive population cluster, albeit related to European and Middle Eastern non-Jewish populations. Within the study, each of the Jewish populations formed its own cluster as part of the larger Jewish cluster. Each group demonstrated Middle Eastern ancestry and variable admixture with European populations. There was evidence of a split between Middle Eastern Iraqi and Iranian Jews and European/Syrian Jews compatible with the historical divide which occurred more than 2,500 years ago.
These studies demonstrate that over the past 3000 years, both the flow of genes and the flow of religious and cultural ideas have contributed to Jewishness.
(1) Origins of Old Testament Priests. Thomas MG, Skorecki K,et al. Nature 394 138-140, 1998.
(2) The genome-wide structure of the Jewish people. Behar DM, Yunusbayev B et al. Nature Letters 1-6 June 9, 2010.
(3) Abraham’s Children in the Genome Era. Atzmon G, Hao L, et al. The American Journal of Human Genetics 86, 850-859, 2010.