The largest study to date of ancient DNA from Jewish individuals reveals unexpected genetic subgroups in medieval German Ashkenazi Jews and sheds light on the “founder event” in which a small population gave rise to most present-day Ashkenazi Jews.
The findings, spearheaded by geneticists from The Hebrew University of Jerusalem and Harvard Medical School, were published Nov. 30 in Cell.
About half of Jewish people around the world today identify as Ashkenazi, meaning that they descend 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 the Rhineland in western Germany.
Despite much speculation, many gaps exist in our understanding of the origin of Ashkenazi Jews and the demographic upheavals they experienced during the second millennium.
To answer some of these pressing questions, the 30-person team — led by Shai Carmi at The Hebrew University and David Reich at HMS — analyzed DNA from the remains of 33 individuals buried in a medieval Jewish cemetery in Erfurt, Germany.
Erfurt’s medieval Jewish community existed between the 11th and 15th centuries, with a short gap following a massacre in 1349. At times, it thrived and was one of the largest Jewish communities in Germany. Following the expulsion of all Jews in 1454, the city built a granary on top of the Jewish cemetery.
In 2013, the granary stood empty and the city permitted its conversion into a parking lot. This required additional construction and an archaeological rescue excavation. The genetics team received a special permit from the local Jewish community, which allowed the researchers to retrieve DNA from detached teeth that had already been collected as part of the rescue excavation.
The analysis revealed two distinct subgroups within the remains: one with greater Middle Eastern ancestry, which may represent Jews with origins in Western Germany, and another with greater Eastern and Central European ancestry. The modern Ashkenazi population formed as a mix of these groups and absorbed little to no outside genetic influences over the 600 years that followed, the authors said.
Some disease-causing mutations that are widespread in modern Ashkenazi Jews are suspected to have been introduced by members of the founding group long ago. The team found some of these mutations in Erfurt as well, indicating that the medieval Ashkenazi population indeed originated from an extremely small set of founders.
Further evidence came from mitochondrial DNA, which is part of the genome transmitted only from mothers. Analyses showed that one third of the Erfurt individuals descended in their maternal line from a single ancestral woman, again highlighting how small the founding population must have been, the authors said.
Despite the insights it provides, the study was limited to one cemetery and one time period. The researchers hope it will pave the way for future analyses of samples from other sites, including those from antiquity, to continue unraveling the complexities of Jewish history.
-
A Deeper Dive
Co-senior author Shai Carmi offers further perspective on the work.What is still unknown about the history of Ashkenazi Jews?
Current studies are still ambiguous regarding the founder event. When exactly did it happen? Was it a single catastrophic event or a continuous decline over centuries? Where did the founders live? Information on the origin of Ashkenazi Jews is also lacking. Where did the Ashkenazi Jewish founders and their ancestors come from? Did early Ashkenazi Jews descend from Judean Jews, or were they converts from other areas in the Mediterranean?
Finally, the Ashkenazi population is genetically homogeneous today. Was it equally uniform in the past? Were Jews from different communities in Northern Europe related only culturally or also genetically? Did the Ashkenazi Jewish gene pool change over the years due to intermarriage with Jews from other communities or with non-Jews?
What was the purpose of the study?
DNA from present-day individuals encodes information on past demographic events. However, DNA from people who lived during the events, or ancient DNA, can be orders of magnitude more informative. Ancient DNA can document migrations as they occur or demonstrate the continuity of populations. It can also tell us about the size of a population, marriage patterns, or ancestry differences between relatives.
Given that no DNA sequences existed for historical Ashkenazi Jews, we sought to generate ancient DNA data for this population. Our hope was to fill the gaps in our understanding of Ashkenazi Jewish early history. Naturally, we do not expect a single dataset to address each and every open question. Nevertheless, we hoped to illuminate some aspects of Ashkenazi Jewish demography during the Middle Ages.
What are the main points we learned about Ashkenazi history?
Put together, our work generated several new insights:
- Ashkenazi Jews had already acquired their main sources of genetic ancestry by the 14th century, including from Eastern Europe. There was little change in those ancestry components in the 600 years that followed.
- In contrast, the internal genetic structure of Ashkenazi Jews has changed over the years. Medieval Ashkenazi Jews are best viewed not as a single homogeneous community (as it came to be at present), but as an archipelago of communities, differentially affected by founder events and mixture with local populations.
- Specifically, we identified a division between one medieval group genetically similar to present-day Ashkenazi Jews from Western Europe, who may represent the descendants of the Rhineland Ashkenazi Jews, and another group with additional Eastern European ancestry, who may represent medieval Ashkenazi Jews from Central and Eastern Europe, who were at the time culturally and linguistically distinct from Western Ashkenazi Jews.
- A key source of pre-medieval Ashkenazi Jewish ancestry is related to people living today in Mediterranean Southern Europe.
- The Ashkenazi Jewish population was characterized by a very small population size during the first centuries of the second millennium. Consequently, late medieval Ashkenazi Jews already carried disease-causing and other variants that have drifted to higher frequencies in Ashkenazi Jews compared to neighboring populations.
First author Shamam Waldman performed most of the data analysis as a doctoral student in Carmi’s group. She is now starting a postdoctoral research position in the Reich lab. Reich is professor of genetics in the Blavatnik Institute at HMS and professor of human evolutionary biology at Harvard University.
The study was funded by the Israel Science Foundation (grant 407/17), United States–Israel Binational Science Foundation (grant 2017024), U.S. National Science Foundation (grants 1912776 and 0922374), U.S. National Institutes of Health (grants GM100233 and HG012287), the Allen Discovery Center program (a Paul G. Allen Frontiers Group advised program of the Paul G. Allen Family Foundation), John Templeton Foundation (grant 61220), a private gift from Jean-François Clin, and the Howard Hughes Medical Institute.
Adapted from a news release by The Hebrew University.
