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Cracking the Code

Spring 2008 coverThe latest DNA research offers extraordinary insights into our people’s origins and its impact on each of us. To tell us what cracking the Jewish code has revealed, RJ editors Aron Hirt-Manheimer and Joy Weinberg turned to Jon Entine, author of Taboo: Why Black Athletes Dominate Sports and Why We’re Afraid to Talk About It and, most recently, Abraham’s Children: Race, Identity, and the DNA of the Chosen People.

How did you come to explore cutting-edge DNA research as a window into our Jewish origins?

For years I’ve been studying how evolution has influenced the body types and the abilities of different groups of people. Then, five years ago my sister Judith learned she had breast cancer, and she immediately did something that wasn’t available to my mother, my aunt, and my grandmother, all of whom had died of either breast or ovarian cancer: she got a genetic test that confirmed she carried the mutation for a genetic form of breast cancer known as BRCA2, one of three breast or ovarian cancer mutations that is found only in Jews or descendants of Jews, and one of more than forty genetic diseases that are especially common in Jews. In essence my sister is a Jew by DNA. I, too, have been diagnosed with this mutation; and I’m particularly concerned because my daughter, who is the product of a mixed marriage, has a fifty-fifty chance of carrying this same Jewish genetic mutation for breast or ovarian cancer. I set out on a journey to learn more.

When you talk about different “groups of people” genetically, how does that differ from categorizing by “race”?

With recent advances in genetics, we now know that grouping people by race, making distinctions by such superficial characteristics as skin color, is a very simplistic and misleading way of describing human diversity. Today, geneticists use the terms “ancestry” or “populations” when describing how groups of people have evolved. Let me give you an example from sports to explain the change in thinking. Different sports tend to be dominated by different population groups, and scientists are convinced that genetics plays a large part in explaining why. In the Olympics, Eurasian whites dominate field events—hammer, shot-put, and javelin—as well as weightlifting. Africans are the world’s best runners, but East and West Africans differ significantly. With their slender upper bodies and what are called slow-twitch muscles, which are great for endurance, East Africans (e.g., Kenyans, Tanzanians, Ethiopians) tend to dominate middle- and long-distance events. In contrast, West Africans, such as Nigerians and their descendants, including African Americans, have more quick-firing, fast-twitch muscle fibers and smaller lung capacities—very efficient characteristics for sprinting and jumping but terrible for distance running. If you look at the top 500 times in the 100-meter, 494 of them are held by a person of West African ancestry, yet not a single person of West African ancestry is an elite long-distance runner; and there are no elite East African sprinters. These two populations share a similar skin color, but they have evolved differently under different evolutionary pressures—the West Africans at sea level, and the East African in the mountains of the Rift Valley. So scientists today allow for a much more complex understanding of human differences, studying distinctive “populations,” which have different body types, disease proclivities, and even behaviors. Because of their cohesive history, Jews are considered a genetic goldmine.

Besides the fact that Ashkenazic Jews have genes that increase their chances of getting certain diseases, what else have we learned from genetic markers?

Genetic anthropologists have been able to test the accuracy of Jewish history and certain Jewish oral traditions. The big breakthrough in Jewish genetics occurred in 1995 when Canadian nephrologist Karl Skorecki and other Jewish geneticists designed an ingenious experiment to find out whether the kohanim (descendants of the ancient Jewish priestly class—a distinct heritage that originated with Moses’ brother Aaron but is now passed down orally from father to son) could in fact be verified by genetics. The male or Y chromosome doesn’t change from father to son, except for random mistakes/mutations, which occur at a fairly regular rate and which offer geneticists what amounts to a date stamp. Based on what’s known about how these mutations evolve, scientists can identify them on the male chromosome and determine when they first appeared. The more mutations two or more people share in common, the more recently they share a common ancestor. Skorecki reasoned that Jewish males who claim to be kohanim, or descendants of Aaron, should have an identical set of marker mutations that trace back to biblical times. So the researchers gathered saliva from 200 Jewish males, a third of whom identified themselves as kohanim, at the Western Wall during the High Holidays. Remarkably, no matter whether they were Sephardic, Ashkenazic, or Oriental Jews, 98.5% of those who said they were kohanim shared a genetic marker for a common ancestor, a signature mutation pattern found in only 3% of the general Jewish population.

The following year, a more extensive, refined study found a set of marker mutations common to approximately 60% of self-proclaimed kohanim. Using complex mathematical calculations the now-expanded research team identified what they dubbed the Cohan Modal Haplotype (CMH), a series of six genetic markers common to the kohanim, which, to their astonishment, originated more than 3,000 years ago—approximately the time of the biblical Aaron, the first kohan.

This remarkable finding raised the tantalizing question: Were there ways to test whether most Jews—bound by ancestry, land, and faith—are the literal descendants of people who lived in the land of Israel more than three millennia ago? DNA suddenly became a way to piece together our people’s story.

What was the next step in the quest to trace Jewish origins genetically?

There have long been questions, with obvious political repercussions, about whether modern Jews are mostly converts or whether they trace their ancestry to the ancient Israelites. In the late 1990s, the original CMH researchers, joined by an all-star roster of geneticists from the U.S., Europe, South Africa, and Israel, initiated a massive study focusing on the male lineage which they hoped would draw a definitive picture of Jewish ancestry. They sampled the DNA of nearly 1,400 males, Jews and non-Jews, from around the world in search of common date markers, and what they discovered was breathtaking. The overwhelming majority of Jewish populations throughout the world—whether Ashkenazic Jews, Sephardic Jews, Indian Jews, Oriental Jews, or Black African Jews (except for the Black Jews of Ethiopia, known as the “Falashas”)—share a common Middle Eastern ancestry on the male line that goes back to ancient Israel 4,000 years ago, when, according to the Bible, Abraham founded the Israelite line. In other words, as the lead researcher Michael Hammer commented, “We are really a single ethnic group coming from the Middle East. Even if you look like another European, with blue eyes and light skin, your [male] genes are telling that you’re from the Middle East.”

Do you mean to say that this is proof that the Abraham of Genesis really lived at that time?

We have to be careful about what DNA can and cannot tell us. It can prove common ancestry, but it cannot prove that Abraham, Moses, or Aaron actually existed. That’s why DNA works in tandem with the findings of research in genealogy, history, and anthropology.

Based on the anthropological and genetic record, we’ve been able to ascertain that the core Israelite population was not a single homogenous population, as the Bible says, but really an amalgam of local populations—Canaanites, Semites, and others—who merged in one form or another over many centuries and achieved a kind of tribal unity by about 1000 B.C.E., during the time of King Solomon. DNA then begins to come into play again after the development of a worldwide Jewish diaspora, which began in the aftermath of the Assyrian invasion of the Northern Kingdom in the 8th century B.C.E. and again after the destruction of the First (586 B.C.E.) and Second (70 C.E.) Temples in Jerusalem. For example, DNA research now confirms that groups in China and India are likely descendants of Israelites from the First Temple period.

The origins of Sephardic Jewry can also be traced to the destruction of the First Temple, when a large segment of Jewish refugees from the Land of Israel settled on the Iberian Peninsula—Spain and Portugal—as well as in northern Africa. By the end of the first millennium of the Common Era, Sephardic Jewry had emerged as the preeminent cultural and population center of the Jewish world, enjoying its Golden Age in the 10th–13th centuries, a time of harmonious relations among Jews, Muslims, and Christians. During the 15th century, after Christianity overran formerly Muslim Iberia, many Sephardic Jews converted—some willingly but many under duress. In 1492 the remaining Jews of Spain and North Africa, who at their peak had numbered close to one million, were given an ultimatum: convert to Christianity or leave the kingdom. The community was shattered, and those who chose to remain Jewish were forced to find a safe haven elsewhere. Many Sephardim converted; some maintained secret Jewish rituals, as crypto Jews, although the Jewish allegiance of these converso families faded over time. For centuries, the Sephardim had followed the strict religious restrictions on intermarriage, but after the expulsion many intermarried, particularly those who relocated to the Netherlands.

The trajectory of the Ashkenazic population is different. Ashkenazic Jewry did not begin to trickle into Europe until the 8th and 9th centuries of the Common Era, when pockets of Jews, mostly from what is now Italy, settled in sections of the Rhine Valley, which runs from the Atlantic Ocean all the way south along the western border of Germany and the eastern border of Switzerland. Most of these male Jews were traders brought north by Christian nobility to help facilitate commerce in the region; in other cases they became moneylenders or tax collectors, functions barred to Christians by the Church. Some came with wives, but it’s believed that most came alone and married local women. These pocket communities moved eastward during the Middle Ages, but remained tiny in size, with Ashkenazic Jewry believed to number no more than 25,000 in total well into the 14th century. That created what geneticists call a population bottleneck. Jewish diseases and other characteristics that developed as the result of mutations quickly spread through these tight-knit, endogamous communities.

Can we track the female line of Jews?

Yes. Just as the human male line can be traced by identifying date markers found on the Y chromosome, which remains essentially unchanged except for mutations that occur infrequently over time, there is a female complement to this: mitochondrial DNA. Mitochondria are the energy engines found in almost all cells in both males and females. Like the male chromosome, female mitochondria not only combine from generation to generation, they get passed down from a mother to female offspring because of the mitochondria found in the egg.

What does the DNA show about the female ancestry among Ashkenazim?

Interestingly, while DNA evidence shows that 80% or more of Jewish males have direct Semitic ancestry, two major studies of Jewish female lineage suggest that only about 50% of females trace their ancestry back to the Middle East. The other 50% or so of Ashkenazic women today—and this is contested territory among genetic researchers—appear to be descended from gentiles. Studies of mitochondrial DNA sampled from hundreds of Jewish women suggest that wandering Jewish men, from Italy or elsewhere, established a mosaic of small Jewish communities scattered through Europe. They often took on gentile wives and raised their children as Jews.

Does that mean many Ashkenazic Jews are descended from gentiles on their maternal side?

Yes. If these wives of Jewish traders did not undergo formal conversion (we’ll never know how many did, but it’s likely many did not), then they and their offspring would not be considered Jews according to halachah (traditional Jewish law), which determines Jewish identity by matrilineal descent. It’s a fascinating point, especially when you consider the State of Israel’s policy of refusing citizenship under the Law of Return to Jews who cannot prove their Jewish ancestry. How many of Israel’s own Ashkenazic Jewish citizens may in fact not be Jews by DNA?

Might this theory explain why so many Ashkenazic Jews have blue eyes?

While until recently the rate of non-Jewish lineages entering Ashkenazic Jewry has been incredibly small—about 0.5% per generation—it is still more than enough to explain why Jews resemble the people within the societies in which they’ve lived. As much as 30% or more of the Ashkenazic gene pool, since its founding, represents a mixture of local populations, accounting for large variations in hair, eye color, physiognomy, and even blood type.

External appearance, in short, is unhelpful in determining Jewish ancestry. DNA research of male and female lineages has shown, for example, that certain tribes in Africa and India have Jewish roots.

Which tribes?

For over a century the 50,000-member Lemba tribe in southern Africa has insisted they are of Jewish ancestry. DNA testing has found that tribe members do have Jewish genetic markers; and, moreover, that 53% of the males in the tribe’s priestly clan (the Buba) carry the kohanim/priestly markers, suggesting that the Lemba’s roots go back more than 3,000 years to the time of the founding of the Jewish population in biblical Israel.

DNA tests have also provided Jewish genetic witness for the Bene Israel, or Sons of Israel, in India, a 4,000-member tribe that long claimed to be related to the ancient Israelites (although they fiercely reject being called Jews, as they believe they are not descendants of the southern kingdom of Judeans but Galilean descendants of the northern tribes). It’s believed that they had little or no contact with other Jews until many of them relocated to Israel in recent years. Yet they have distinct Jewish genetic markers on their Y chromosome—and here, too, some Bene Israel have the priestly markers as well—suggestive evidence that they are also descendants of biblical Israelites.

What does the genetic evidence show about the Jewish origins of Ethiopian Jewry?

The Black Jews of Ethiopia, who were airlifted to Israel in the mid 1980s as part of a massive Jewish rescue of what many believed was a mythical Lost Tribe, have steadfastly claimed a biblical royal pedigree tied to King Solomon and the Queen of Sheba. At the urging of many Orthodox Jews, Israel’s chief rabbis embraced this account and granted them official status as descendants of the lost tribe of Dan. But more recent DNA evidence is not so generous: Ethiopian Jews do not have the Jewish genetic markers seen in all other Jewish groups, which tells us that they don’t have genetic roots in ancient Israel. This finding is in line with historical evidence suggesting that in the 5th or 6th century C.E. a fairly sizable number of Ethiopians, including some of the royalty, converted to Judaism. Still, they have remained faithful to Judaism for 1,500 years—longer than the history of Ashkenazic Jewry.

For the groups that have received DNA confirmation of their Jewish ancestry, the news must be empowering.

Oh yes, having genetic witness to their ancestral Israelite roots has provided these communities with cultural cohesiveness, a sense of real pride—no one can take it away from them now—and a new level of respect from other Jews.

What does DNA evidence reveal about the conversos in the Southwest United States?

For years a host of anecdotal reports have appeared about people in the American Southwest and northern Mexico who practice Jewish rituals such as lighting candles on Friday evenings and covering the mirrors after a family member has died. Occasionally some claimed they were descendants of Jews, but few people took them very seriously. Cultural anthropologists tended to believe they had adopted the rituals from Jewish traders. Thanks to genetic research, however, we can now confirm that many of these individuals and pocket communities do, in fact, have Jewish roots. In my book I tell the story of William Sanchez from Albuquerque, New Mexico, who had always wondered about the Jewish-like rituals in his family. After he saw a story on genetic genealogy on PBS he sent in a DNA sample for testing. When the lab reached him on the phone and said, “Mr. Sanchez, we found some interesting results from your DNA; you may be descended from or closely related to priests,” Sanchez replied, “That makes perfect sense, because I am a priest.” There was stunned silence on the phone because William Sanchez was, in fact, a Catholic priest. He and many of his family members have since pieced together their family history and discovered that they—as well as many Hispanos in Sanchez’s congregation and in communities throughout the Southwest—are the descendants on their male side of Sephardic Jews who converted to Catholicism and then settled in the New World, where they took on Native American wives. Over time the descendants’ Jewish practices atrophied and they became Christian in belief. Nowadays, to celebrate their Jewish heri­tage alongside their Catholic beliefs, Sanchez and many of his parishioners wear a Star of David with a cross in the middle. Interestingly, too, a few of his family members have been touched so deeply by this revelation, they have converted to Judaism.

Although we say there are only about 13–15 million Jews in the world, I would guess that if we tested everybody in the world, tens of millions of people would have traces of a Jewish past.

There’s been so much intermixing. Going back ten generations, we each have about 1,000 ancestors, which means we share about one millionth of a random neighbor’s DNA by direct descent. Twenty-five generations ago, about the time when Columbus landed on America’s shores, the number of our ancestral cousins swells to an astronomical 30 million, almost all of the world’s population at that time. We already spoke of the Sephardic Jews who were forced to convert in 1492. There were also forced conversions to Islam at various times in history.

More recently, think of how many Jewish women gave up their sons and daughters during the Holocaust, passing them off to Christians to be raised. And think of other Jews who, for various reasons, chose to hide their Jewish roots from succeeding generations. I tell the story in my book of the pioneer geneticist Mary-Claire King, who identified BRCA1, the first of three Jewish breast cancer mutations. She was raised Protestant and taught that she was a daughter of the American Revolution. It wasn’t until she was in college that her mother, Clarice, revealed to her that her paternal grandfather was named Cohen, indicative of the kohan (Jewish priestly) line. Clarice had hidden her ancestry after being persecuted by the KKK in Tulsa, Oklahoma and being rejected by Wellesley College because the school had “fulfilled its quota of Jewish women”—this despite Clarice’s having graduated as number one in her high school class. So she officially took her mother’s maiden name and kept the name change secret. Fascinated by the revelation, Mary-Claire decided to switch her major from mathematics to genetics; and the result has been a historical breakthrough in Jewish genetic medical research.

Is the study of Jewish genetics making inroads in medicine?

It’s literally saving thousands of lives around the world. There are some forty known “Jewish diseases,” disorders that originated in single Jews and then spread throughout Jewish communities. You can inherit some genetic disorders from either a mother or father—the breast cancer mutations are examples. But many diseases, such as Tay-Sachs, result from the virulent combination of mutations carried by both.

The great breakthrough in genetic disease screening happened a few decades ago, when the genetic markers for Tay-Sachs were identified and a test became available. But because Orthodox Judaism strictly prohibits abortion, as well as premarital and prenatal testing, and most of the Tay-Sachs victims and carriers were living within the Orthodox community in Crown Heights, Brooklyn, the Tay-Sachs scourge continued. This changed in 1983, when Rabbi Josef Ekstein, a leader of the Brooklyn Lubavitcher community and father of a four-year-old son who had died of Tay-Sachs, devised a screening system whereby all Orthodox children are tested well before they are of marriage age, no names are collected, everyone is issued a coded number, and before a couple announces their engagement, they are informed whether they are genetically incompatible. The number of babies born with Tay-Sachs in the U.S. has now dropped from fifty a year to five.

This model of genetic testing has now essentially been adopted worldwide in communities where marriage between close kin is common. In villages within Israel’s West Bank, for example, there are Arab communities where villagers have lived within a circumscribed 50-square-mile radius for centuries. Even if residents don’t think they’re marrying a cousin, they may very well be marrying a cousin. That’s led to a host of inbred genetic disorders, like congenital deafness. But now these models of screening pioneered by Jews are helping Arabs and others throughout the world.

From an evolutionary point of view, then, it’s healthy to bring people from other communities into the Jewish community, so the Jewish gene pool doesn’t become so homogenous.

From this perspective, yes, intermarriage is great; it’s what geneticists call hybrid vigor. In mixing populations genetically, we’re assuring that future Jewish generations will be healthier. From a genetic and Jewish cultural continuity perspective, however, the best of all possible worlds is for Jews to marry non-Jews who convert to Judaism.

You’ve pointed to the very positive aspects of genetic testing. But isn’t it also true that the same technology can be used to discriminate?

Understandably, there’s great fear that because of genetic research, people will be labeled defective and subject to discrimination by medical insurers. If my daughter does carry the genetic defect for breast cancer, insurers might very well discriminate against her, because her chances of developing cancer during her lifetime would be quite sizable compared to the general population. And if we’ve learned anything from history, science can be hijacked by the purveyors of such racist theories as eugenics. Therefore we desperately need to discuss the implications of human genome research to ensure that its focus is enlightenment and not enslavement.

What is likely to be the next breakthrough in genetic research that can shed light on the Jewish people?

Well, the first phase of genetic research, when in 2001 the crude human genome map was unveiled, emphasized the shared ancestry of all humanity. At the time, Francis Collins, the head of the Human Genome Project, commented: We are more than 99% the same. I call that the Kumbaya period of genetic research, which underscored that we are all one species. But that’s not where genetic research is headed. The future is focused on curing diseases, and to do that we must get into the prickly subject of human differences based on our ancestry. We are different populations, with differences in brain architecture, appearance, abilities, and disease proclivities. As yet we don’t fully understand how these differences have evolved, but within ten or fifteen years, each of us will literally be able to carry a genetic score card of all the major genetic influences on who we are. This will really help us to address the specific genetic disorders afflicting us as Jews. It’s going to be quite a revelation.

Conversations on the Code

Reform Judaism magazine has created a discussion and study guide to this story, "Cracking the Code." Continue the conversation in your home and/or synagogue with this free discussion guide.


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