Jewish law is quite clear on the question ""Who is a Jew?"" (anyone whose mother is Jewish), yet the question remains vexing, calling up issues of religion, history, culture and sometimes politics. In his second foray into the world of genetics and race, Entine (an American Enterprise Institute fellow and author of Taboo: Why Black Athletes Dominate Sports and Why We're Afraid to Talk About It) shows the degree to which genetics has been thrown into the mix. He presents fascinating evidence from DNA studies: the genes of Jewish males around the world can be traced back to the ancient Middle East; the genes of Jewish women cannot. Among Africans who claim Jewish ancestry, the Falashas of Ethiopia do not have Jewish genetic markers; but the less well known Lemba of South Africa do. A majority of cohanim, or priests, have a common genetic marker, but Levites (of whom priests are supposedly a subset) do not. But Entine can be sloppy (his grasp on the respective roles of high priests, priests and Levites is shaky; he seems unclear whether the Pilgrims were Quakers or Puritans), and he digresses from science to potted history, myths about the 10 Lost Tribes and an account of his trip to the West Bank. More problematic, his account of genetic science and DNA analysis is vague. Entine's final chapters broach the contentious topics of whether one can speak genetically of race and whether ""Jewish genes"" confer intellectual superiority on Ashkenazi Jews. While he cites scientists, some of the assumptions and conclusions (such as that medieval Jews' role as moneylenders contributed to a high IQ) are speculative.