[Paleopsych] NYT: New Light on Origins of Ashkenazi in Europe
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Sat Jan 14 10:38:30 UTC 2006
New Light on Origins of Ashkenazi in Europe
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
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,
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.
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