An international team analyzing DNA from the teeth of 33 Ashkenazi Jews who lived in the 14th century in Erfurt, Germany, found that the Jewish community then was more genetically diverse than its modern-day descendants.
The study, led by researchers at the Hebrew University of Jerusalem and Harvard University in Massachusetts, was published in the journal Cell under the title “Genome-wide data from medieval German Jews show that the Ashkenazi founder event predated the 14th century.”
About half of Jews today are identified as Ashkenazi, meaning they originated from Jews who lived in Central or Eastern Europe. The term was initially used to define a distinct cultural group of Jews who settled in the 10th century in Germany’s Rhineland.
The gaps in the origin story of Ashkenazi Jews
Despite much speculation, many gaps exist in our understanding of their origins and demographic upheavals during the second millennium.
“Today, if you compare Ashkenazi Jews from the US and Israel, they’re very similar genetically, almost like the same population regardless of where they live. But unlike today’s genetic uniformity, it turns out that the community was more diverse 600 years ago.”
Prof. Shai Carmi
“Today, if you compare Ashkenazi Jews from the US and Israel, they’re very similar genetically, almost like the same population regardless of where they live,” said Hebrew University geneticist and co-author Prof. Shai Carmi. “But unlike today’s genetic uniformity, it turns out that the community was more diverse 600 years ago.”
The research team of over 30 scientists included the Hebrew University’s Shamam Waldman, a doctoral student in Carmi’s group, who performed most of the data analysis.
The team discovered that the community can be categorized into two groups. One relates more to individuals from Middle Eastern populations and the other to European populations, possibly including migrants to Erfurt from the East. The findings suggest that there were at least two genetically distinct groups in medieval Erfurt, but that genetic variability no longer exists in modern Ashkenazi Jews.
The Erfurt medieval Jewish community existed between the 11th and 15th centuries, with a short gap following a 1349 massacre. At times, it was a thriving community and one of the largest in Germany. After the expulsion of all Jews in 1454, the city built a granary on top of the Jewish cemetery. In 2013, when the granary stood empty, the city permitted its conversion to a parking lot, requiring additional construction and an archaeological rescue excavation.
“Our goal was to fill the gaps in our understanding of Ashkenazi Jewish early history through ancient DNA data,” explained Carmi. While ancient DNA data is a powerful tool to infer historical demographics, ancient Jewish DNA data is hard to come by, as Jewish law prohibits the disturbance of the dead in most circumstances. With the approval of the local Jewish community, the research team collected detached teeth from remains found in a 14th-century Jewish cemetery in Erfurt that underwent a rescue excavation.
The researchers also discovered that the founder event – which makes all Ashkenazi Jews today descendants of a small population – occurred before the 14th century. For example, teasing through mitochondrial DNA, genetic materials inherited from our mothers, they discovered that a third of the sampled Erfurt individuals shared one specific sequence. The findings indicate that the early Ashkenazi Jewish population was so small that a third of Erfurt individuals descended from a single woman through their maternal lines.
At least eight of the Erfurt individuals also carried disease-causing genetic mutations common in modern-day Ashkenazi Jews but rare in other populations – a hallmark of the Ashkenazi Jewish founder event.
“Jews in Europe were a religious minority that was socially segregated, and they experienced periodic persecution,” described the study’s Harvard University co-author, David Reich. Although antisemitic violence virtually wiped out Erfurt’s Jewish community in 1349, Jews returned five years later and flourished as one of the largest in Germany. “Our work gives us direct insight into the structure of this community.”
The team believes the current study helps to establish an ethical basis for studies of ancient Jewish DNA. Many questions remain unanswered, such as how medieval Ashkenazi Jewish communities became genetically differentiated, how early Ashkenazi Jews related to Sephardi Jews, and how modern Jews relate to ones from ancient Judea.
While this is the largest study of ancient Jewish DNA so far, it is limited to one cemetery and one period of time. However, it was able to detect previously unknown genetic subgroups in medieval Ashkenazi Jews. The researchers hope their study will pave the way for future analyses of samples from other sites, including those from antiquity, to continue unraveling the complexities of Jewish history.
“This work also provides a template for how a co-analysis of modern and ancient DNA data can shed light on the past,” concluded Reich. “Studies like this hold great promise not only for understanding Jewish history, but also that of any population.”