In DNA, New Clues to Jewish Roots

"The new study, by Dr. David Goldstein, Dr. Mark Thomas and Dr. Neil Bradman of University College in London and other colleagues, appears in The American Journal of Human Genetics this month. Dr. Goldstein said it was up to historians to interpret the genetic evidence. His own speculation, he said, is that most Jewish communities were formed by unions between Jewish men and local women, though he notes that the women's origins cannot be genetically determined.

'The men came from the Near East, perhaps as traders,' he said. 'They established local populations, probably with local women. But once the community was founded, the barriers had to go up, because otherwise mitochondrial diversity would be increased.'
In ancient Israel, the Jewish priesthood was handed from father to son. But at some time from 200 B.C. to A.D. 500, Jewish status came to be defined by maternal descent. Even though the founding mothers of most Jewish communities were not born Jewish, their descendants were.
'It's precisely that custom that allows us to see these founding events,' Dr. Goldstein said.

Like the other Jewish communities in the study, the Ashkenazic community of Northern and Central Europe, from which most American Jews are descended, shows less diversity than expected in its mitochondrial DNA, perhaps reflecting the maternal definition of Jewishness. But unlike the other Jewish populations, it does not show signs of having had very few female founders. It is possible, Dr. Goldstein said, that the Ashkenazic community is a mosaic of separate populations formed the same way as the others.

Dr. Harry Ostrer, a medical geneticist at New York University, said the 26 specific genetic diseases found among Ashkenazim, usually attributed to 'founder effects,' could be"