"Jewish populations around the world share more than traditions and laws—they also have a common genetic background," says the New Scientist about a study performed at NYU. "In a study of over 200 Jews from cities in three different countries, researchers found that all of them descended from a founding community that lived 2500 years ago in Mesopotamia. Harry Ostrer of New York University, whose team carried out the study, likens modern Jewish populations to a series of genetic islands spread across the world. The main reason that Jews continue to form a distinct genetic group, despite their wide dispersal is the exclusivity of the Jewish religion and the tight restrictions it imposes on marriage to those outside the Jewish faith."