Monday, January 13, 2014

Highlight: Out of Khazaria—Evidence for “Jewish Genome” Lacking

 Hebrew language and Jewish culture have been around for thousands of years. For much of that history, the Jews managed to maintain their heritage and cultural identity in the absence of a geographical state. Wanderings, settlements, and dispersal were thus a big part of their history. Is evidence for that history preserved in genome data?
Eran Elhaik, a geneticist at the Johns Hopkins School of Public Health, thinks so. In a recently published study in Genome Biology Evolution(Elhaik 2012), he is calling for a rewrite of commonly held assumptions about Jewish ancestry. Instead of being primarily the descendants of the 12 tribes of Israel, present-day Jewish populations are, finds Elhaik, primarily the children of a Turkish people who lived in what is now Russia, north of Georgia, east of Ukraine. This civilization, the Khazars, converted from tribal religions to Judaism between the 7th and 9th centuries.
The controversy cut into by Elhaik's work runs deep, far past the lab bench. Among some circles, his conclusions are bound to be unpopular. “This is the first scientific paper to prove the Khazarian Hypothesis and reject the Rhineland Hypothesis,” he says, “and with it about 40 years of research.” Although his findings will not be welcome in all circles, Elhaik's interest is more medical than political.
“All I want is to help my colleagues who are studying genetic disorders,” he says. “I hope this work will open up a new era in genetic studies where population stratification will be used more correctly.”
Jewish populations are used in many disease studies because of their presumed genetic homogeny. Some conditions, such as Tay–Sachs disease, are more common among select Jewish populations than other populations. However, Elhaik says, the acceptance of a flawed origin narrative is hampering the best science.
For several decades, two hypothetical backgrounds of present-day European Jews have seemed plausible to historians and geneticists. In the favored “Rhineland Hypothesis,” Jews descended from Israelite–Canaanite tribes who left the Holy Land for Europe in the seventh century, following the Muslim conquest of Palestine. Then, in the beginning of the 15th century, a group of approximately 50,000 left Germany, the Rhineland, for the east. There they reproduced rapidly, in a kind of “hyper–baby boom.” Their breeding outpaced their non-Jewish neighbors by an order of magnitude—despite disease, persecutions, wars, and economic hardship—ballooning to approximately 8 million strong by the 20th century. Under this history, European Jews would be very similar to each other and would have Middle Eastern ancestry.
Several scholars prefer the “Khazarian Hypothesis,” Elhaik included. This suggests the Jewish-convert Khazars, with reinforcements from Mesopotamian and Greco-Roman Jews, formed the basis of Eastern Europe's Jewish population when they fled northeast, following the collapse of their empire at the 13th century.
Elhaik first became fascinated by this idea 10 years ago when reading Arthur Koestler best-selling book The Thirteenth Tribe, published in 1976. Koestler calculated that Jews could not have numbered 8 million in Eastern Europe without the Khazar contribution. Upon reading his ideas, “I couldn’t wait for genetic data that would allow someone to publish an evaluation of this hypothesis,” says Elhaik.