Genetic studies on Jews are part of the population genetics discipline and are used to better understand the chronology of migration provided by research in other fields, such as history, archaeology, linguistics, and paleontology. These studies investigate the origins of various Jewish populations today. In particular, they investigate whether there is a common genetic heritage among various Jewish populations.
Studies of autosomal DNA, which look at the entire DNA mixture, show that Jewish populations have tended to form relatively closely related groups in independent communities, with most in a community sharing significant ancestry. For populations of the Jewish diaspora, the genetic composition of Ashkenazi, Sephardi, and Mizrahi Jewish populations show a predominant amount of shared Middle Eastern ancestry. According to Behar and colleagues (2010), this is "consistent with the historical formulation theories the Jewish people as descending from ancient Hebrew and Israelites of the Levant" and "the dispersion of the people of ancient Israel throughout the Old World". Jews living in the North African, Italian, and Iberian regions show variable frequencies of admixture with the historical non-Jewish host population along the maternal lines. In the case of Ashkenazi and Sephardi Jews (in particular Moroccan Jews), who are closely related, the source of non-Jewish admixture is mainly southern European. Behar and colleagues have remarked on an especially close relationship between Ashkenazi Jews and modern Italians, particularly Tuscans.
Since the 1970s, many studies have attempted to determine whether common ancestors existed to the present Jewish communities or if the descendants are related instead to the non-Jewish populations where they lived.
The earlier studies tried to answer this question using "classic" genetic markers (blood groups, enzymes, etc.). Contradictory answers were given according to the loci used. One explanation for these contradictions is that the variations associated with a locus are influenced by natural selection. Since the late 1980s and especially since the beginning of the twenty-first century, geneticists have worked on analysis of the Y chromosome (transmitted from father to son), or mitochondrial DNA (transmitted from mother to child), which have the characteristic to be transmitted in full (without recombination). It is possible to trace the common direct-line ancestral populations of various peoples of the world.
A new genetic map paints a comprehensive picture of the 2,000 or so years in which different Jewish groups migrated across the globe, with some becoming genetically isolated units while others seemed to mix and mingle more.
The new findings allow researchers to trace the diaspora, or the historical migration, of the Jews, which began in the sixth century B.C. when the Babylonians conquered the Kingdom of Judah. Some Jews remained in Judah under Babylonian rule, while others fled to Egypt and other parts of the Middle East. Jewish migrations have continued into the present day.
The study researchers found that the genomes of Jewish North African groups are distinct from one another, but that they show linkages to each other absent from their non-Jewish North African neighbors. The findings reveal a history of close-knit communities prone to intermarriage, said study leader Harry Ostrer of the Albert Einstein College of Medicine in New York.
"Virtually all the Jewish groups we've studied tend to be quite closely related to one another," Ostrer said. "It would seem for most Jewish groups, there is a biological basis for their Jewishness which is based on their sharing of DNA segments."
TRACING JEWISH GENETICS
Ostrer and his colleagues have been studying the genetics of Jewish groups throughout Europe and the Middle East, both to reconstruct the history of the religion and to investigate diseases such as the genetic disorder Tay-Sachs that disproportionately affect this population. In 2010, the group reported on the genetics of seven European and Middle Eastern populations. The new study, published today (Aug. 6) in the journal Proceedings of the National Academy of Sciences, expands the findings to a total of 15 groups, with the newest additions from Morocco, Algeria, Tunisia, Libya and the island of Djerba.
The researchers worked with local communities to get volunteers to offer blood samples for genetic analysis. The current study analyzed the genes of 509 unrelated North African individuals, comparing them across groups. Similar work has been done linking ancient Israeli and Syrian people to Ethiopia.
The results revealed close relations between North African and European Jews, Ostrer said. The researchers also found two distinct groups of North African Jews, one comprised of Libyan and Tunisian Jews and the other of Moroccan and Algerian Jews. These groups were more likely to share DNA segments than other Jewish groups, indicating more shared genetic history.
"I like to think of Jewishness as a tapestry with these DNA segments representing the threads that weave the tapestry together,"Ostrer said. Non-Jews can convert to Judaism, but membership in the group is also passed down along a matrilineal line, meaning Jewishness straddles the line between religion, ethnicity and culture.
A HISTORY OF MIGRATION
The findings tended to track with what is known of the history of the Jewish Diaspora, or spread of the Jewish people, through North Africa. For example, there was evidence of gene-sharing between North African Jews and non-Jews, but generally not recently, the researchers found.
"This tends to fit the historical observation that during Islamic times from roughly the eighth century to roughly the 20th century, there was limited intermarriage between Jews and non-Jews," Ostrer said.
Among Moroccan and Algerian Jews, there was evidence of some mixing with the Sephardic Jews who trace their roots to the Iberian Peninsula. Again, the genetic results back up the known history of Sephardic Jews leaving Spain and Portugal, with some settling in Morocco and Algeria.
The findings help create a "comprehensive view of what the Jewish Diaspora was like,"Ostrer said. Major times of movement included the classic period of Greek and Roman dominance, when Jewish groups migrated out of the Middle East and into Europe and North Africa, converting locals and intermarrying along the way. A second major migration occurred after the Spanish Inquisition in the late 1400’s and early 1500’s, a time when Jews and Muslims were ordered to convert to Catholicism or leave Spain. [10 Myths of Medieval Torture]
The most recent movement began in the late 1800’s and continues today, with immigration to the United States, Israel, Canada, Australia and South Africa, Ostrer said.
The United States and Latin America tend to be a "melting pot" of genetics, Ostrer said — 50 percent to 60 percent of American Jews marry someone of a different religion or ethnicity — but the "Old World" genetics of European and North African Jews are helpful in understanding certain diseases.
In these populations, people married within their communities and even within their own families for centuries, allowing studies on relatively few people to be extrapolated more widely throughout the population. In a similar example, researchers recently found a gene that protects against Alzheimer's disease in Icelandic populations. Those results were reported July 21 in the journal Nature. The same sort of research is possible in Jewish populations, Ostrer said. "It represents an extraordinary resource that is much harder to do, for instance, in the European-American population, because there has been such a melting pot occurring there."
WHAT WE CAN LEARN FROM THE JEWISH GENOME Newsweek, Sharon Begley June 2010
Jews have historically considered themselves "people of the book" (am hasefer in Hebrew), referring to sacred tomes, but the phrase is turning out to have an equally powerful, if unintended, meaning: scientists are able to read Jewish genomes like a history book.
Jews have historically considered themselves “people of the book” (am hasefer in Hebrew), referring to sacred tomes, but the phrase is turning out to have an equally powerful, if unintended, meaning: scientists are able to read Jewish genomes like a history book. The latest DNA volume weighs in on the controversial, centuries-old (and now revived in a 2008 book) claim that European Jews are all the descendants of Khazars, a Turkic group of the north Caucasus who converted to Judaism in the late eighth and early ninth century. The DNA has spoken: no.
In the wake of studies in the 1990s that supported biblically based notions of a priestly caste descended from Aaron, brother of Moses, an ambitious new project to analyze genomes collected from Jewish volunteers has yielded its first discoveries. In a paper with the kind of catchy title you rarely see in science journals—“Abraham’s Children in the Genome Era”—scientists report that the Jews of the Diaspora share a set of telltale genetic markers, supporting the traditional belief that Jews scattered around the world have a common ancestry. But various Diaspora populations have their own distinct genetic signatures, shedding light on their origins and history. In addition to the age-old question of whether Jews are simply people who share a religion or are a distinct population, the scientific verdict is settling on the latter.
Although the origin of the Jews has been traced, archeologically, to the Middle East in the second millennium B.C.E., what happened next has been more opaque. To sort it out, researchers collected DNA from Iranian, Iraqi, Syrian, and Ashkenazi Jews around New York City; Turkish Sephardic Jews in Seattle; Greek Sephardic Jews in Thessaloniki and Athens; and Italian Jews in Rome as part of the Jewish HapMap Project. (All four grandparents of each participant had to have come from the same community.) As the scientists will report in the next issue of the American Journal of Human Genetics, the analysis shows that “each of the Jewish populations formed its own distinctive cluster, indicating the shared ancestry and relative genetic isolation of the members of each of those groups.”
Jewish populations, that is, have retained their genetic coherence just as they have retained their cultural and religious traditions, despite migrations from the Middle East into Europe, North Africa, and beyond over the centuries, says geneticist Harry Ostrer of NYU Langone Medical Center, who led the study. Each Diaspora group has distinctive genetic features “representative of each group’s genetic history,” he says, but each also “shares a set of common genetic threads” dating back to their common origin in the Middle East. “Each of the Jewish populations formed its own distinctive cluster, indicating the shared ancestry and relative genetic isolation of the members of each of those groups.”
The various Jewish groups were more related to each other than to non-Jews, as well. Within every Jewish group, individuals shared as much of their genome as two fourth or fifth cousins, with Italian, Syrian, Iranian, and Iraqi Jews the most inbred, in the sense that they married within the small, close-knit community. In general, the genetic similarity of any two groups was larger the closer they lived to one another, but there was an exception: Turkish and Italian Jews were most closely related genetically, but are quite separated geographically.
Historical records suggest that Iranian and Iraqi Jews date from communities that formed in Persia and Babylon, respectively, in the fourth to sixth centuries B.C.E., and the DNA confirms that. The genetic signatures of these groups show that they remained relatively isolated—inbred—for some 3,000 years. The DNA also reveals that these Middle Eastern Jews diverged from the ancestors of today’s European Jews about 100 to 150 generations ago, or sometime during the first millennium B.C.E.
That’s when the Jewish communities in Italy, the Balkans, and North Africa originated, from Jews who migrated or were expelled from Palestine and from people who converted to Judaism during Hellenic times. During that period Jews proselytized with an effectiveness that would put today’s Mormons to shame: at the height of the Roman Empire, as the Roman historian Josephus chronicled, mass conversions produced 6 million practicing Jews, or 10 percent of the population of the Roman Empire. The conversions brought in DNA that had not been part of the original gene pool in the land of Abraham.
The DNA analysis undermines the claim that most of today’s Jews, particularly the Ashkenazi, are the direct lineal descendants of converted Khazars—which has angered many in the Jewish community as an implicit attack on the Jews’ claim to the land of Israel, since it implies that today’s Jews have no blood ties to the original Jews of the Middle East. Instead, find the scientists, at most there was “limited admixture with local populations, including Khazars and Slavs ... during the 1,000-year (second millennium) history of the European Jews.”
Of the non-Jewish Europeans, northern Italians were most genetically similar to the Jews, followed by the Sardinians and French. The Druze, Bedouins, and Palestinians were closest to the Iranian, Iraqi, and Syrian Jews. That is evidence of “a shared genetic history of related Middle Eastern and non-Semitic Mediterranean ancestors who chose different religious and tribal affiliations.” Adds Ostrer, “the study supports the idea of a Jewish people linked by a shared genetic history. Yet the admixture with European people explains why so many European and Syrian Jews have blue eyes and blond hair.”
Southern Europeans were the closest genetic cousins of Ashkenazi, Sephardic, and Italian Jews, reflecting the large-scale conversion of these Southern European populations to Judaism some 2,000 years ago, when European Jewry was forming. The Sephardic groups share genetic makers with North Africans, probably a result of marriages between Moors and Jews in Spain from 711 to 1492.
Several details of the Ashkenazi genome imply that centuries ago, the population experienced a severe bottleneck, in which the size of a group plummets, followed by a rapid expansion. That jibes with the historical record showing that the Jewish population in Western and Eastern Europe bottomed out at about 50,000 in the Middle Ages and then soared to 500,000 by the 19th century, growing at twice the rate of non-Jews—something called “the demographic miracle.”
Analysis of Jewish genomes has been yielding fascinating findings for more than a decade. A pioneer in this field, Michael Hammer of the University of Arizona, made the first big splash when he discovered that genetics supports the biblical account of a priestly family, the Cohanim, descended from Aaron, the brother of Moses: one specific genetic marker on the Y chromosome (which is passed on from father to son, as membership in the priestly family would be) is found in 98.5 percent of people who self-identify as Cohanim, he and colleagues reported in a 1997 paper in Nature (the PBS science series Nova did a nice segment on that work, summarized here). The Cohanim DNA has been found in both Ashkenazi and Sephardic Jews, evidence that it predates the time when the two groups diverged, about 1,000 years ago. DNA can also be used to infer when particular genetic markers appeared, and suggests that the Cohanim emerged about 106 generations ago, making it fall during what is thought to be the period of the exodus from Egypt, and thus Aaron’s lifetime.
HISTORY AND GENETICS: CAN THE HISTORY OF THE JEWS ACTUALLY BE OBSERVED IN THEIR GENOMES Part 1
The purpose of this study is to relate the substantial discoveries made in the study of the genetics of the Jewish people with the substantial progress made in the study of their history in modern times. While the study of Jewish genetics is a relatively new field, Jewish history continues to progress due to new data becoming available and also new perspectives and methodologies. Actually, the study of the genome is fast becoming one of those new methodologies as the boundaries between what were very distant fields appear to be eroding. Indeed, our purpose here is to hasten this process by attempting to test the results of genetic studies against various models of demographic development.
We will present the material largely according to a geographic classification. However, before beginning, we need to make clear that there are a variety of models of Jewish population movement that contribute to the overall spread of Jewish population throughout the world. Since we will encounter a number of these in our discussion, it would be worth surveying the possible forms for the establishment of communities that underlie the discussion that follows. At the conclusion of our paper, we will want to sum up the various forms of population movement that we have discussed.
At the outset we should say that there are several models for Jewish population movement that we will encounter in the historical and genetic evidence:
Migration of small family or tribal groups.
Establishment of business centers on trade routes.
Mass migration resulting from Exodus, exile or expulsion.
Voluntary migration for economic advantage.
Involuntary migration resulting from political upheaval or war.
A word about our purpose in this paper is necessary. These observations are important not only to the presentation that follows, but to much of what has been written about Jews and genetics. The job of the historian of the Jews is to use all available sources to reconstruct Jewish history. It is not to seek proofs or disproofs of Jewish traditional or political claims. While we are all aware of the relevance of the research that we are discussing here to such issues, our job is to steer clear of such polemical research and to make use of genetic evidence as a factor in our understanding of the history of the Jewish people and their spread throughout the world.
HISTORY AND GENETICS: COMMONALITY OF ORIGIN Part II
The issue of the common origin of the Jews has been greatly illuminated by genetic study. Jews from the ancient Land of Israel were dispersed into the wider Diaspora communities, through a whole series of events including emigration, exile and long-term business travel that resulted in the founding of far-flung Jewish communities. Genetic evidence has tended to provide a number of indications of elements common to the main population groups of the Jewish people, Ashkenazim, Sephardim (by which we refer to the Spanish Portuguese Jews and their descendents) and Middle Eastern Jews. The method of coalescence has been used to determine that the particular mutations causing certain diseases occurred some 2000 years ago, when the main body of the Jewish population was still in the Land of Israel. This is the case with Familial Mediterranean fever and with the BRCA1 and 2 genes that give rise to breast and ovarian cancer. One of these mutations has been found among Jews from all over the world, including Bene Israel and some Hispanics who may be descendents of Conversos. Again, such features indicate the common genetic origin of the Jews. All this is in confidence with our understanding of the common historical origin of the Jewish people. Investigation of the Y chromosome has shown that most Diaspora Jews are descended from a small group of men who at some time lived in the Middle East. In this case, the resemblance of these men to other Middle Eastern males indicates the likelihood that the Jewish community did for the most part in fact emanate from Middle East antiquity.
The Jewish HapMap Project has found that Ashkenazic, Sephardic and Syrian Jews were more similar to one another than to Middle Eastern, Iranian and Iraqi Jews. This genetic split seems to have occurred approximately 2500 years ago. Over the last 2000 years the European and Syrian populations were formed by people expelled from or who voluntarily left Palestine as well as by non-Jews who joined the Jewish people, a phenomenon well-known to have occurred during Greco-Roman antiquity.