Excerpted with permission from New Voices, the national Jewish student magazine and part of the JewZ.com network.

The Center for Human Genetics at New York University is filled with the constant hum of busy students, doctors, and patients. There's nothing to indicate that the work researchers are doing here has the potential to radically alter millennia-old conceptions of Jewish peoplehood.

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Incongruous as the setting might seem, though, scientists at the Center for Human Genetics are investigating some of the most fascinating and longstanding questions of Jewish history. Dr. Harry Ostrer, the head of the center, is one of the many scientists around the world using the tools of modern genetic research to uncover the ancient roots of the Jewish people, long the exclusive province of historians. The results of genetic research could have a tremendous impact on the way Jews view themselves and their community.

The recent investigations into Jewish origins are, in some ways, a natural outgrowth of earlier studies of genetic diseases. Jews have long been a favored test group for research on genetic susceptibility to certain diseases. Centuries of living behind ghetto walls and marrying amongst themselves created Jewish populations with relatively homogenous gene pools, making the genetic variations linked to specific diseases easier to spot.

As a medical student at Columbia University in the 1970s, Ostrer, who is Jewish himself, helped to organize a Tay-Sachs screening program in the Bronx. (Tay-Sachs is an inherited syndrome common in Ashkenazi Jews.) As the amount of genetic data he collected grew, he, like many other Jewish scientists, began to wonder what other information might be hiding in his database.

"Eventually," he says, "we developed a rather marvelous database of DNA samples. And then, since we were studying Ashkenazi Jews, we figured 'why not look at other [Jewish] populations as well, and look at origins.'"

Now, many scientists who began their careers studying genetic diseases are employing the same research techniques to delve into the historical roots of the modern Jewish people.

Most of a person's DNA is a unique combination of contributions from that person's mother's and father's DNA. However, in men, the DNA on the Y-chromosome (the male sex chromosome) is inherited only from the father. So a man's Y-chromosome DNA is essentially a duplicate of his father's, his paternal grandfather's, and so on through the generations.

But it's not always an exact duplicate. Occasionally, random mutations will occur in DNA as it is passed from parent to child. If this DNA contains the instructions for something important, say the number of fingers and toes, the mutation could have significant consequences. Fortunately, only about two to three percent of a person's DNA actually contains genetic instructions. The rest has no known purpose and is called "junk DNA." Mutations that occur in the junk DNA are passed on from generation to generation, without causing any harm.

It is these changes in DNA that give scientists a window into the past. The more similar two men's Y-chromosome junk DNA, the fewer generations it must have had to mutate, and the more recently the men must have had a common ancestor. Scientists can find specific combinations of DNA markers, called haplotypes, that are essentially DNA mutations that have been handed down over generations and are indicative of certain population groups. By comparing the haplotypes that are prevalent in two populations' DNA, researchers can tell how closely the two populations are related.

Recently, a group of scientists, led by Dr. Michael Hammer at the University of Arizona, used this method to conduct the most extensive and in-depth study of Jewish origins ever attempted. Hammer, working with NYU's Harry Ostrer and other scientists around the world, examined the DNA of 1371 men from 29 populations, both Jewish and non-Jewish. The Jewish populations included, among others, Ashkenazim, North Africans, Yemenites, and Ethiopians. The non-Jewish populations included Russians, Italians, Sub-Saharan Africans, Syrians, Lebanese, and many others.

The results, which were published the Proceedings of the National Academy of Sciences, indicated a high genetic correlation among Jews from all over the world. An Ashkenazi Jew from Russia was likely to be more genetically similar to a Syrian Jew than to an ethnic Russian. In addition, Jews generally were very genetically similar to non-Jewish Syrians, Palestinians, and Lebanese, indicating that nearly every Jewish population can trace its roots back to the Middle East. The only Jewish group that did not fit into this scheme were the Ethiopians, who were very similar to non-Jewish Ethiopians, and not at all similar to other Jews.

Although this is the most extensive genetic study of Jewish origins to date, it was not the first. A 1997 study led by Karl Skorecki, a kidney disease researcher now at the Technion-Israel Institute of Technology, examined the DNA of dozens of Jewish men, both Ashkenazim and Sephardim. Some of the men were Cohanim, a title given to those who are supposedly direct descendents through the male line of First and Second Temple-era priests, and going back even further, of Moses' brother Aaron. The researchers located a "Cohen Modal Haplotype," a set of genetic markers that were present in only about 10% of non-Cohen Jews, but over half of all Cohanim--pointing to a single common ancestor for most Cohanim, and supporting the accuracy of centuries of oral tradition.

The notion that all of the Jews in the world descend from a common pool of Middle Eastern ancestors is central to Jewish identity. The idea that Jews in all corners of the globe are physically descended from those people who stood with Moses at Mt. Sinai is a powerful glue helping to bind the Jewish community together.

Over the years, though, that tradition has been contested by historians who have claimed that significant Jewish populations are descended not from the Middle Eastern forebears at Mt. Sinai, but instead from later converts to Judaism. The most famous of these theories is the one that well-known scholar Arthur Koestler proposed in his 1976 book, "The Thirteenth Tribe." Koestler argued that most Ashkenazi Jews descend from the Khazars, a Turkic people whose leaders converted to Judaism sometime during the eighth century, and may have taken the mass of their subjects along with them.

Although this theory has generally found little favor among Jewish historians, it and others like it have sown seeds of doubt about the genetic unity of the Jewish people. And until very recently, there was no way to prove or disprove these theories' validity. But by demonstrating that Jews all over the world are genetically similar to each other, Hammer and his colleagues have confirmed that the Jewish community is, in the most literal sense, one people. "I think we've shown," Harry Ostrer says, "that Jews are demonstrable as a people with a genetic affinity that can be demonstrated over a 4,000 year period."

One would think that most rabbis and other Jewish authorities would be pleased by this turn of events, and many of them are. Lawrence Schiffman, chair of the department of Hebrew and Judaic Studies at New York University, sees the research in a mostly positive light. "The advantage of [these studies]," he says "is to make clear to Jews the extent to which the spiritual, educational, and identity heritage of the Jewish people has been carried through familial relationship for so long. They support the notion of there being a continuous, intergenerational relationship that is simultaneously religious, cultural, ethnic, and genealogical/familial."

Some rabbis and scholars, though, are a bit less enthusiastic. One of these is Arthur Hertzberg, a Conservative rabbi and author. Asked whether he believes this type of research to have any benefits or dangers for the Jewish people, he says simply "neither. Research is research. This is pure scientific research. We take for granted that Jews go back to a Middle Eastern ancestor."

Even those people who find the studies affirming are concerned about some of their possible implications. Many see the possibility that some misinformed people could think that genetics is a way to determine Jewishness as one of this research's greatest dangers. Explains Rabbi Avi Shafran, spokesman for the ultra-Orthodox group Agudath Israel, "[Genetic testing] wouldn't be able to rule anyone out as a Jew, because conversion is always an option. We're a very exclusive club, we Jews, but totally open to anyone who wants to join."

There is another reason that some Jewish authorities are reluctant to wholeheartedly embrace this research. Even now, more than 50 years after the end of the Holocaust, anything that smacks of defining Jews as a race can have frightening connotations. Although he generally approves of the research, Lawrence Schiffman concedes, "I think we all know that racial science fed into anti-Semitism, and certainly into the Nazi type of anti-Semitism."

The studies of the past several years have hardly closed the book on the question of modern Jews' ancestry. Right now, two separate research groups are taking a more in-depth look at the origins and migration patterns of Eastern European Jews. Michael Hammer and Harry Ostrer are leading one study; Dr. Vivian Moses and Dr. Neil Bradman are conducting the other at the Center for Genetic Anthropology at University College-London.

Vivian Moses suggests that the results of his study might diverge somewhat from what Hammer and his colleagues presented last June. "I think perhaps we are using more DNA markers than they did," he says, "and therefore the results might not be exactly the same. We already have some preliminary indications of a link between [Eastern European Jews and] Slavs."

If it does become apparent that some Eastern European Jews are more closely related to Slavs than to Middle Easterners, that will certainly provoke more discussion among rabbis and Jewish scholars. Most see the results of the already-published studies as an affirmation of the unity of the Jewish people--but not, they say, a necessary one. From the ultra-Orthodox to the secular, Jewish leaders say the notion of Jewish peoplehood and Jewish unity is, in essence, independent of genetic evidence. And, given the possibility that future studies may produce disaffirming results, that may be a wise stance to take.

This article is reprinted from New Voices, a part of the JewZ.com Media Network.