Study: Ashkenazi Jews Have Become More Genetically Similar over Time

A study of skeletons unearthed from a medieval Jewish cemetery in Germany has revealed a surprising genetic split among Ashkenazi Jews of the Middle Ages that no longer exists.

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

“That is wild!” said Dr. Harry Ostrer, a medical geneticist at the Albert Einstein College of Medicine in the Bronx and a co-author of the new study. “Despite the rapid growth of the Ashkenazi Jewish population during the last 700 years, the population became more homogeneous.”

The study, published on 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 from around the world. Previous studies have shown that modern communities are a genetic mélange, with Ashkenazim the world over 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, dating back to a small founder population that most likely emigrated from Southern Europe and reached the German Rhineland at the turn of the first millennium. But the DNA analysis also revealed a genetic divide among the skeletons, which could have several explanations. In one scenario, both groups originated from the Rhineland. One branch then stuck around the region, while the other headed east to modern-day Poland, Czech Republic, Austria and eastern Germany.

Alternatively, Eastern Europe might 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 fairly isolated from each other for generations, as evidenced by their discrete genetic lineages. Then, prompted by massacres, expulsions and economic opportunities, they reunited in places like Erfurt, the central German city that is home to the cemetery where the remains were disinterred.