theory that the ancestors of Polish Jewry were Jews who came from the Crimean Jewish kingdom of Khazaria", describing Koestler as the "best-known advocate" of the theory. In 2009, Jeffrey Goldberg wrote that the book was "a combination of discredited and forgotten [ideas]". Koestler biographers have also been critical of the work. In Arthur Koestler: The Homeless Mind (1998), David Cesarani states it makes "selective use of facts for a grossly polemical end" and is "risible as scholarship". In Koestler: The Literary and Political Odyssey of a Twentieth-Century Skeptic (2009), Michael Scammell writes that Koestler's theory "was almost entirely hypothetical and based on the slenderest of circumstantial evidence", and takes the book as evidence that Koestler's brain "was starting to fail him". Genetic research A 2005 study by Nebel et al., based on Y chromosome polymorphic markers, showed that Ashkenazi Jews are more closely related to other Jewish and Middle Eastern groups than to the populations among whom they lived in Europe. However, 11.5% of male Ashkenazim were found to belong to Haplogroup R1a, the dominant Y chromosome haplogroup in Eastern Europeans, suggesting possible gene flow. Referencing The Thirteenth Tribe, the study's authors note that "Some authors argue that after the fall of their kingdom in the second half of the 10th century CE, the Khazar converts were absorbed by the emerging Ashkenazi Jewish community in Eastern Europe." They conclude: "However, if the R-M17 chromosomes in Ashkenazi Jews do indeed represent the vestiges of the mysterious Khazars then, according to our data, this contribution was limited to either a single founder or a few closely related men, and does not exceed ~ 12% of the present-day Ashkenazim". Writing in Science, Michael Balter states Koestler's thesis "clash[es] with several recent studies suggesting that Jewishness, including the Ashkenazi version, has deep genetic roots." He refers to a 2010 study by geneticist Harry Ostrer which found that Ashkenazi Jews "clustered more closely with Middle Eastern and Sephardic Jews, a finding the researchers say is inconsistent with the Khazar hypothesis" and concludes "that all three Jewish groups—Middle Eastern, Sephardic, and Ashkenazi—share genomewide genetic markers that distinguish them from other worldwide populations". Geneticist Noah Rosenberg asserts that although recent DNA studies "do not appear to support" the Khazar hypothesis, they do not "entirely eliminate it either." Publication details References 1976 non-fiction books Books by Arthur Koestler Ashkenazi Jews topics Khazar studies Judaism-related controversies History books