UK scientists have discovered that a medieval mass burial shows a much earlier origin of an Ashkenazi genetic ‘bottleneck’.

Almost 20 years ago, construction workers in Norwich, UK, unearthed human skeletal remains at the bottom of a medieval well. Using archaeological records, historical documents, and ancient DNA, British researchers have now identified the remains of at least 17 individuals to be a group of Ashkenazi Jews who may have fallen victim to antisemitic violence during the 12th Century.

The Natural History Museum’s Ian Barnes, evolutionary geneticist, and corresponding author, said: “It’s been over 12 years since we started looking into who these people were, and the technology finally caught up with our ambition. Our main job was to establish the identity of those individuals at the ethnic level.”

The deceased individuals were found to carry some genetic disorders, for which modern-day Ashkenazi Jewish populations are at higher risk. Genetic disorders that are particularly common in certain populations can arise during bottleneck events, where a rapid reduction of population can lead to big jumps in the number of people carrying otherwise rare genetic mutations.

Using computer simulations, the team showed that the number of such disease mutations in the remains was similar to what they would expect if the diseases were as common then as they are now in Ashkenazi Jews. The results point to a bottleneck event that shaped the modern-day Ashkenazi Jewish population prior to the 12th Century, earlier than previous beliefs, which dated the event about 500 to 700 years ago.

Unlike other mass burial sites, where bodies were laid in an organized fashion, skeletons from this well were oddly positioned and mixed, most likely because they were deposited head-first shortly after death. Archaeological investigations reported six adults and 11 children at the unusual burial location. Together, these findings hint at mass fatalities such as famine, disease, or murder. Radiocarbon dating of the remains placed their deaths around the late 12th to early 13th century—a period with well-documented outbreaks of antisemitic violence in England—leading researchers to consider foul play.

Co-author Mark Thomas, an evolutionary geneticist at the University College London, added: “It was quite surprising that the initially unidentified remains filled the historical gap about when certain Jewish communities first formed and the origins of some genetic disorders. Nobody had analysed Jewish ancient DNA before because of prohibitions on the disturbance of Jewish graves. However, we did not know this until after doing the genetic analyses.”

The findings appear in the journal Current Biology.

Image: Based on the skeletal remains, scientists reconstructed the face of a male adult (left) and a child (right) © Professor Caroline Wilkinson, Liverpool John Moores University