For the new analysis, published in the Proceedings of the National Academy of Sciences, Ostrer and his colleagues examined the genomes of 509 Jews and 11 non-Jews from North Africa, which is home to the second-largest Jewish diaspora. Only the European diaspora, which includes American Jews, is larger.

Basically - it all started from same people came out of same location in the Middle East. And each Jewish population in diaspora setting kept marrying within themselves.