Ashkenazi Jews have become genetically more similar over time

Ashkenazi Jews have become genetically more similar over time

A study of skeletons discovered in a medieval Jewish cemetery in Germany has revealed a startling genetic divide among medieval Ashkenazi Jews that no longer exists.

The analysis, the first of its kind from a Jewish cemetery and the product of years-long negotiations between scientists, historians and religious leaders, shows that Ashkenazim have become genetically more similar over the past seven centuries. Two Jews walking the cobblestone streets of 14th-century Germany were on average more genetically distinct than two Ashkenazi Jews alive today.

“It’s wild!” said Dr. Harry Ostrer, a medical geneticist at Albert Einstein College of Medicine in the Bronx and co-author of the new study. “Despite the rapid growth of the Ashkenazi Jewish population over the past 700 years, the population has become more homogeneous.”

The study, published Wednesday in the journal Cell, compared DNA extracted from the teeth of 33 men, women and children buried in the cemetery with DNA taken from hundreds of modern Jews around the world. Previous studies have shown that modern communities are a genetic mix, with Ashkenazim around the world carrying essentially the same collection of DNA sequences.

But the medieval remains tell a different story. They show that European Jews at the time came from two divergent gene pools.

Each group shared the same genetic ancestry, tracing back to a small founding population that most likely migrated from southern Europe and reached the German Rhineland around the turn of the first millennium. But DNA analysis also revealed a genetic divide between the skeletons, which could have several explanations. In one scenario, both groups are from the Rhineland. One branch then stuck in the region, while the other headed east into today’s Poland, Czech Republic, Austria and East Germany.

Alternatively, Eastern Europe could have been settled by a different population of Jews who then mixed to a limited extent with their Jewish neighbors to the west.

Either way, the two groups remained quite isolated from each other for generations, as evidenced by their discrete genetic lineages. Then, driven by massacres, evictions and economic opportunity, they gathered in places like Erfurt, the city in central Germany that is houses the cemetery where the remains were exhumed.

“It’s a super cool study,” said Itsik Pe’er, a computational geneticist at Columbia University who wasn’t involved in the research. “Ancient DNA sequencing is a cheat code that can take you to places where you don’t have information today.”

The existence of an East-West community in Erfurt is also supported by the historical record, which includes detailed accounts of a violent pogrom on March 21, 1349 – a Saturday. Angry mobs entered the local synagogue and attacked Jews in the midst of prayer. Few, if any, survived.

After the massacre, the rulers of Erfurt took possession of goods and property. They even collected debts owed to murdered Jews. But just five years later, the need for lost tax revenue prompted the city to invite Jews back.

They have come from afar. Tax records show names indicating origins from all over Europe – including some from distant towns that have seen their own anti-Semitic upheavals. “In the middle of German-speaking lands, this was the place to be back then,” said Maria Stürzebecher, a medievalist and curator of the Erfurt Old Synagogue Museum. At least, that is until 1453, when the Jews were again expelled.

The same migration patterns could be observed in the excavated teeth.

Isotope readings of tooth enamel showed that many people were migrants who had grown up elsewhere. But DNA took this discovery one step further, showing that the Jews of Erfurt came from several places and that these populations were genetically distinct.

“This evidence both raises new questions and confirms stories we’ve been telling for a long time,” said Elisheva Baumgarten, a social historian at the Hebrew University of Jerusalem who was not involved in the study.

Preserved records of moneylending practices show that Jews in each subgroup largely formed trading alliances with members of their own species, according to Maike Lämmerhirt, a historian at the University of Erfurt and co – author of the study. But the two groups prayed in the same synagogue. They all cleaned themselves in the same ritual bath. And, finally, they all rest side by side in the same cemetery.

The Erfurt skeletons carried many of the same disease-causing genetic mutations that Ashkenazi Jews worry about today. This suggests that a population bottleneck must have occurred before the Erfurtians were born – a bottleneck in which a small number of individuals seeded an entire population, leading to genetic similarities and the amplification of certain gene variants.

Scientists had previously calculated that the Ashkenazi Jewish population bottleneck event occurred around 600 to 800 years ago. But the new study, along with a British study published this year that examined six 12th-century skeletons found in England, suggest it could have been even older.

“Given the date of these samples, we really put it at the very, very old end of those estimates,” said Mark Thomas, an evolutionary geneticist at University College London who led the UK study.

“If you put the two papers together, they agree completely – which is pretty cool,” said Ron Pinhasi, an anthropologist and geneticist at the University of Vienna in Austria who was not involved in either study.

Rabbinic law generally disapproves of the exhumation of corpses, out of concern for the dignity of the dead. Scientists therefore cannot excavate Jewish graves purely for academic intrigue.

But what happened in Erfurt had nothing to do with the scientists.

In 2013, a warehouse built above the cemetery more than 500 years earlier was transformed into a parking lot. Karin Sczech, an archaeologist at the time with the state preservation office, knew the construction might disrupt some ancient Jewish remains.

dr. Sczech came to the site a day before the excavation work began, to find that the contractor had already started digging. Inside the bucket of an actively digging excavator were the bones of a small child.

“I yelled at the driver and said ‘stop’,” recalls Dr Sczech, now UNESCO World Heritage Coordinator for Erfurt.

She and her team uncovered 47 graves in an area roughly the size of a volleyball court. In consultation with the local Jewish community, archaeologists meticulously removed the skeletons and brought them back to local archives.

There the bones sat for many years. The plan had been to rebury the bodies quickly, once scientists had a chance to study the remains. But the anthropologist involved in the effort found himself tied up, causing a year-long delay.

Luckily for genetic science it did. Had the anthropologist been quicker, the skeletons would have been back in the ground before the geneticists who led the new study, David Reich of Harvard and Shai Carmi of the Hebrew University of Jerusalem, knew of their existence.

Researchers set out in 2017 to find an ancient Jewish cemetery being excavated, hoping to be able to collect a small sample for genetic testing.

Dr. Carmi took the lead. He sought the advice of Ephraim Shoham-Steiner, a historian at Ben-Gurion University of the Negev, Israel. “I said, ‘If there’s a place where this could really come into play, it would be in Erfurt,'” Dr Shoham-Steiner recalls.

At first, the Chief Rabbi of Erfurt rejected the idea. There are situations that allow DNA testing of Jewish corpses – for example, families of Yemeni children who disappeared in the early years of Israel’s establishment can request that the graves be opened for forensic identification .

But the reasoning in these cases centered on concrete benefits to the deceased. The scientific research done on anonymous bodies is different.

Dr Carmi consulted with a judge from a rabbinical court in Israel – Rabbi Ze’ev Litke, founder of the Simanim Institute in Jerusalem, which helps people determine if they have Jewish ancestry through genetic testing – who ruled that it would be permissible to isolate DNA from teeth or tiny bones detached from the inner ear which, unlike the remains of a skeleton, do not require reburial under Jewish law.

Convinced by the argument, the Rabbi of Erfurt changed his mind. The project was launched. Dr. Sczech found that 38 of the skeletons had at least one loose tooth.

Soon, Dr. Reich was returning to Boston with zipper bags full of medieval molars, premolars, and incisors. Using techniques that won this year’s Nobel Prize in Physiology or Medicine, Dr. Reich and his colleagues managed to extract DNA from 33 teeth.

The scientists hope their approach to community engagement will provide a roadmap for others hoping to examine DNA from ancient remains, whether they come from Jewish cemeteries or not. “It’s really kind of a prototype of what can be done in similar studies,” Dr. Reich said.

Views differ among authorities on Jewish law, or Halakha, as to whether obtaining DNA during an archaeological dig from known Jews is above all else.

Rabbi Myron Geller, an expert on Jewish funeral practices and a former member of the Conservative movement’s Committee on Jewish Law and Standards, described the reasoning adopted by Rabbi Litke and the study’s authors as “the strongest halachic perspective possible “.

But others have questioned whether the abstract benefits of scientific knowledge are sufficient grounds for deserving the desecration of the dead. “It makes me think,” said Rabbi Joseph Polak, chief justice of the Massachusetts Rabbinical Court.

On a recent trip to Yad Vashem, the Holocaust memorial atop Mount Herzl in Jerusalem, Dr. Carmi wandered through the Valley of the Communities. In this massive monument to the destroyed Jewish communities, he found the name Erfurt. Just like in medieval times, hundreds of Jewish residents of Erfurt were murdered during the Nazi era.

Standing there, Dr. Carmi pondered the pieces of lost history that her genetic analysis had helped to lay bare. “It was a great honor for me personally to bring their story to life,” he said.

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