[Paleopsych] NYT: New Light on Origins of Ashkenazi in Europe

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New Light on Origins of Ashkenazi in Europe
http://www.nytimes.com/2006/01/14/science/14gene.html

    By NICHOLAS WADE

    A new look at the DNA of the Ashkenazi Jewish population has thrown
    light on its still mysterious origins.

    Until now, it had been widely assumed by geneticists that the
    Ashkenazi communities of Northern and Central Europe were founded
    by men who came from the Middle East, perhaps as traders, and by
    the women from each local population whom they took as wives and
    converted to Judaism.

    But the new study, published online this week in The American
    Journal of Human Genetics, suggests that the men and their wives
    migrated to Europe together.

    The researchers, Doron Behar and Karl Skorecki of the Technion and
    Ramban Medical Center in Haifa, and colleagues elsewhere, report
    that just four women, who may have lived 2,000 to 3,000 years ago,
    are the ancestors of 40 percent of Ashkenazis alive today. The
    Technion team's analysis was based on mitochondrial DNA, a genetic
    element that is separate from the genes held in the cell's nucleus
    and that is inherited only through the female line. Because of
    mutations - the switch of one DNA unit for another - that build up
    on the mitochondrial DNA, people can be assigned to branches that
    are defined by which mutations they carry.

    In the case of the Ashkenazi population, the researchers found that
    many branches coalesced to single trees, and so were able to
    identify the four female ancestors.

    Looking at other populations, the Technion team found that some
    people in Egypt, Arabia and the Levant also carried the set of
    mutations that defines one of the four women. They argue that all
    four probably lived originally in the Middle East.

    A study by Michael Hammer of the University of Arizona showed five
    years ago that the men in many Jewish communities around the world
    bore Y chromosomes that were Middle Eastern in origin. This finding
    is widely accepted by geneticists, but there is less consensus
    about the women's origins.

    David Goldstein, now of Duke University, reported in 2002 that the
    mitochondrial DNA of women in Jewish communities around the world
    did not seem to be Middle Eastern, and indeed each community had
    its own genetic pattern. But in some cases the mitochondrial DNA
    was closely related to that of the host community.

    Dr. Goldstein and his colleagues suggested that the genesis of each
    Jewish community, including the Ashkenazis, was that Jewish men had
    arrived from the Middle East, taken wives from the host population
    and converted them to Judaism, after which there was no further
    intermarriage with non-Jews.

    The Technion team suggests a different origin for the Ashkenazi
    community: if the women too are Middle Eastern in origin, they
    would presumably have accompanied their husbands. At least the
    Ashkenazi Jewish community might have been formed by families
    migrating together.

    Dr. Hammer said the new study "moves us forward in trying to
    understand Jewish population history." His own recent research, he
    said, suggests that the Ashkenazi population expanded through a
    series of bottlenecks - events that squeeze a population down to
    small numbers - perhaps as it migrated from the Middle East after
    the destruction of the Second Temple in A.D. 70 to Italy, reaching
    the Rhine Valley in the 10th century.

    But Dr. Goldstein said the new report did not alter his previous
    conclusion. The mitochondrial DNA's of a small, isolated population
    tend to change rapidly as some lineages fall extinct and others
    become more common, a process known as genetic drift. In his view,
    the Technion team has confirmed that genetic drift has played a
    major role in shaping Ashkenazi mitochondrial DNA. But the linkage
    with Middle Eastern populations is not statistically significant,
    he said.

    Because of genetic drift, Ashkenazi mitochondrial DNA's have
    developed their own pattern, which makes it very hard to tell their
    source. This differs from the patrilineal case, Dr. Goldstein said,
    where there is no question of a Middle Eastern origin.