clipped from wiki - of particular importance is the dna evidence - a religious group, as opposed to a tribal ethnic one would have a more diverse gene pool -
Who is a Jew?
Judaism shares some of the characteristics of a nation, an ethnicity, a religion, and a culture, making the definition of who is a Jew vary slightly depending on whether a religious or national approach to identity is used. Generally, in modern secular usage, Jews include three groups: people who were born to a Jewish family regardless of whether or not they follow the religion, those who have some Jewish ancestral background or lineage (sometimes including those who do not have strictly matrilineal descent), and people without any Jewish ancestral background or lineage who have formally converted to Judaism and therefore are followers of the religion....
DNA evidence
A study published by the National Academy of Sciences found that "the paternal gene pools of Jewish communities from Europe, North Africa, and the Middle East descended from a common Middle Eastern ancestral population", and suggested that "most Jewish communities have remained relatively isolated from neighboring non-Jewish communities during and after the Diaspora". Researchers expressed surprise at the remarkable genetic uniformity they found among modern Jews, no matter where the diaspora has become dispersed around the world. The DNA tests demonstrated substantially less inter-marriage among Jews over the last 3,000 years than found in other populations....
Another of the study's findings is that by the yardstick of the Y chromosome, the world's Jewish communities are closely related to Syrians and Palestinians. The study's authors wrote that "the extremely close affinity of Jewish and non-Jewish Middle Eastern populations observed ... supports the hypothesis of a common Middle Eastern origin",as does the mitochondrial DNA of at least 40% of the current Ashkenazi population.
