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Dr. Shaye Cohen, professor of Jewish literature and philosophy at Harvard, said the implication of the findings and the idea of Jewish communities' having been founded by traders, was ''by no means implausible.''

''The authors are correct in saying the historical origins of most Jewish communities are unknown,'' Dr. Cohen said. ''Not only the little ones like in India, but even the mainstream Ashkenazic culture from which most American Jews descend.''

In a recent book, ''The Beginnings of Jewishness,'' Dr. Cohen argued that far-flung Jewish communities had adopted the rabbinic teaching of the matrilineal descent of Jewishness soon after the Islamic conquests in the seventh, eight and ninth centuries A.D.


The data being generated by Dr. Hammer, Dr. Goldstein and other population geneticists touches on the delicate issue of whether Jews can be considered a race. Dr. Cohen noted that the Nazis and their anti-Semitic predecessors had argued that Jews were a race and therefore irreconcilable with the host community and that Jews had in response argued they were not, because they admitted people by conversion.

If the founding mothers of most Jewish communities were local, that could explain why Jews in each country tend to resemble their host community physically while the origins of their Jewish founding fathers may explain the aspects the communities have in common, Dr. Cohen said.

Despite the definition of Jewishness as being born to a Jewish mother, and the likelihood of some continuity between ancient and modern populations, it has not until recently been clear that genetics had anything much to contribute to questions of Jewish identity.

Some scholars suspected that Jewish communities had through intermarriage or conversion become little different from their host populations. Many say they believe that even if Jews are a group definable in ethnic, as opposed to cultural or religious terms, it is either impossible or unwise to define an ethnic group genetically.

Dr. Schiffman said that as president of the Association for Jewish Studies he would consider convening a discussion between the geneticists and the historians on interpreting the new data. He noted that the study of racial differences had led to disaster in the past but that the new analysis of genetic differences was ''a form of racial science for the good, rather than the bad.''

''Racial science,'' Dr. Schiffman said, ''has brought so many terrible things. But it's a norm now in genetics to study the racial genetics of groups. So I think it's an amazing difference.''

Geneticists use the Y chromosome and mitochondrial DNA to track the movement of populations because each is passed unchanged from parent to child, escaping the genetic shuffle that occurs on the rest of genome between generations. Since the Y chromosome passes down only from father to son, and mitochondrial DNA is always inherited from the mother alone, the two elements serve to track the genetic history of men and women respectively.

But since the Y chromosome and mitochondrial DNA clock up occasional changes or mutations every thousand years or so, on much the same time scale as human population splits, different ethnic groups tend to have characteristic patterns of mutations.

The Y chromosome and mitochondrial DNA's in today's Jewish communities reflect the ancestry of their male and female founders but say little about the rest of the genome, which is by now a presumably well mixed set of genes contributed by all the founders of each community.

Noting that the Y chromosome points to a Middle Eastern origin of Jewish communities and the mitochondrial DNA to a possibly local origin, Dr. Goldstein said that the composition of ordinary chromosomes, which carry most of the genes, was impossible to assess.

''My guess,'' Dr. Goldstein said, ''is that the rest of the genome will be a mixture of both.''

Chart/Map: ''How a Diaspora Grew'' Contemporary Jewish populations have origins in three areas: the Iberian peninsula, northern Europe and the Middle East. DNA analysis finds most Jewish communities genetically distinct from neighboring populations, suggesting origins that differ from those given in traditional histories. In the 20th century (not shown), there were major migrations to the Americas and Israel. Map of Europe, Asia, and Africa highlighting early migration routes and the following three locations: Ashkenazi GERMANY Sephardic SPAIN Middle Eastern PALESTINE/ISRAEL (Source: Nature Genetics)