The genetic bottleneck predates medieval times, pushing back the expected date.
Eight centuries after a medieval massacre in Norwich, England, the bones of at least seventeen Jewish victims have yielded a quiet but profound revelation: the genetic patterns long thought to be a relatively recent inheritance of Ashkenazi Jewish communities were already present in the twelfth century. Modern genome sequencing, applied to remains recovered from a well during shopping mall construction, has pushed the timeline of a critical population bottleneck back to the earliest formation of Ashkenazi communities in the Middle Ages. What began as an act of historical violence has become, through science, an unexpected window into the deep roots of a people's biological and cultural identity.
- Skeletal remains of at least 17 Jewish victims, dumped into a Norwich well during an antisemitic riot in 1190, were accidentally rediscovered by construction workers centuries later — a crime scene sealed in time.
- DNA extracted from six of those individuals carries elevated frequencies of genetic disease variants associated with disorders like Tay-Sachs and Gaucher disease, upending the scientific consensus that this risk was a product of the last 500 to 700 years.
- The findings point to a genetic bottleneck during the early formation of Ashkenazi communities, likely when Jews from the Roman Empire migrated northward into Central and Eastern Europe and began marrying within their communities.
- Ancient Jewish DNA is extraordinarily rare in science because religious law typically prohibits disturbing graves, making this accidental discovery — and the community's eventual consent to reanalysis — a singular opportunity.
- A separate study of 33 Ashkenazi individuals from 14th-century Erfurt, Germany, awaiting peer review, appears to corroborate the earlier bottleneck date, suggesting the Norwich findings are not an anomaly but a pattern.
In 1190, members of Norwich's Jewish community were killed in an antisemitic riot during the fervor of the Third Crusade — a period when false accusations, including the notorious blood libel charge, were sweeping across Europe. Their bodies were thrown into a well and forgotten. Centuries later, construction workers breaking ground for a shopping mall stumbled into that sealed crime scene, recovering the skeletal remains of at least 17 people. Radiocarbon dating confirmed the bones matched the historical record of the massacre.
The remains were documented, ritually reinterred, and largely set aside — until 2018, when Norwich's Jewish community asked evolutionary biologist Ian Barnes of the Natural History Museum to reexamine them using modern genome sequencing. What his team found, published in Current Biology, rewrites a chapter of Ashkenazi genetic history. DNA from six of the individuals showed elevated frequencies of disease-causing variants linked to hereditary disorders like Tay-Sachs and Gaucher disease — variants scientists had previously believed concentrated in Ashkenazi populations only within the last 500 to 700 years.
Corresponding author Mark Thomas of University College London argues the evidence points to an earlier genetic bottleneck, most likely during the formation of Ashkenazi communities in the early Middle Ages. The DNA also revealed traces of Italian ancestry, consistent with a migration of Jews northward out of the Roman Empire into Central and Eastern Europe — a movement that likely reduced the gene pool and concentrated certain variants over generations of community endogamy.
Researchers are careful to note that there is no such thing as an "Ashkenazi Jewish genetic disease" — only certain variants that appear at higher frequencies in this population, as regional bottlenecks produce in many groups worldwide. The medieval individuals also showed signs of nutritional deficiency and physical labor, quietly complicating stereotypes about medieval Jewish life.
The study's reach is limited by its small sample, and Thomas acknowledges that population history resists simple narratives. Yet a forthcoming study of 33 Ashkenazi individuals from 14th-century Erfurt appears to support the same earlier timeline. As ancient genome databases grow, and as researchers explore legal pathways — such as analyzing teeth, which Jewish law does not classify as permanent body parts — the story of the Jewish diaspora may come into sharper focus, carried forward, improbably, by the dead.
In 1190, members of Norwich's Jewish community were murdered in an antisemitic riot and their bodies dumped into a well. Eight centuries later, construction workers digging the foundation for a shopping mall in what is now Norwich, England, unknowingly broke through into that crime scene. They found the skeletal remains of at least 17 people.
Radiocarbon dating and pottery analysis placed the bones between the 12th and 14th centuries, aligning with historical accounts of the massacre. The killings occurred during a surge in antisemitism tied to the Third Crusade—a period when false accusations, including the blood libel charge against Jews for the death of a boy named William of Norwich in 1144, were spreading across Europe. The BBC's History Cold Case program documented the discovery in 2011, and the remains were ritually reinterred in a cemetery that same year.
For nearly two decades, the bones sat in archives. Then in 2018, Norwich's Jewish community asked Ian Barnes, an evolutionary biologist at the Natural History Museum, to reexamine the remains using modern genome sequencing technology. What Barnes and his team found, published this week in Current Biology, rewrites the timeline of Ashkenazi Jewish genetic history. The DNA from six of the 17 individuals—combined with computational modeling—revealed that these medieval Jews already carried elevated frequencies of disease-causing genetic variants associated with hereditary disorders like Tay-Sachs disease, Gaucher disease, and familial dysautonomia.
Until now, scientists believed the genetic bottleneck responsible for this heightened risk occurred within the last 500 to 700 years. A genetic bottleneck happens when a population suddenly shrinks, reducing the diversity of the gene pool and concentrating certain variants. Mark Thomas, an evolutionary biologist at University College London and corresponding author on the study, says the evidence points to an earlier origin. "What our data suggests is that we need to push back the date of that bottleneck to before the time of the Chapelfield individuals," Thomas told Inverse, referring to the shopping mall site. "My interpretation is that it's most likely to have been during the formation of Ashkenazi communities in the early Middle Ages." The researchers found genetic evidence of mixing between Jewish and Italian ancestry, suggesting that Jews who had lived in the Roman Empire migrated northward into Central and Eastern Europe—a movement that likely created the bottleneck.
The discovery carries both scientific and historical weight. Karl Skorecki, a molecular geneticist at Bar-Ilan University in Israel who was not involved in the research, called the study "remarkable and at the same time horrific." The work bridges archaeology, DNA analysis, and computational biology in ways rarely possible with ancient Jewish remains. Religious law typically prohibits disturbing graves, making ancient Jewish DNA scarce in scientific literature. These researchers only learned after beginning their analysis that the Chapelfield individuals were likely Jewish—a macabre accident of discovery that made the work possible.
Thomas emphasizes an important distinction: there is no such thing as an "Ashkenazi Jewish genetic disease." Rather, certain genetic diseases occur at higher frequencies in this population, just as different regional groups carry elevated risks for different disorders. The bottleneck and the practice of marriage within the community—endogamy—concentrated these variants. Skorecki clarified that genetic similarity from endogamy does not require incest; it simply results from a community marrying within itself over generations. Barnes added another detail that complicates easy narratives: the medieval individuals showed signs of non-genetic disorders and nutritional deficiencies associated with hard labor, pushing back against stereotypes of wealthy medieval Jews.
The research team identified over 150 locations in the genome where disease-causing variants appear more frequently in Ashkenazi populations than in other groups. They focused their analysis on the six individuals with the best-preserved DNA, using next-generation sequencing and paying special attention to inner ear bones, which are more sealed from environmental contamination and thus more likely to yield human genetic material. Computer simulations then extrapolated whether the patterns in these six individuals reflected the broader population of the time. The findings suggested that disease variant frequencies in the 12th century matched what researchers see in modern Ashkenazi populations.
Thomas acknowledges the limitations: six individuals is a small sample, and population history contains far more nuance than any single study can capture. Yet the work opens new avenues. A paper awaiting peer review examines whole genome sequencing from 33 Ashkenazi Jews from 14th-century Erfurt, Germany, and those findings also support an earlier bottleneck date. Thomas notes that teeth, unlike other bones, are not considered permanent body parts under Jewish law and can therefore be removed and analyzed—a loophole that may allow future researchers to study more ancient remains. As databases of ancient genomes grow, he says, the chances of understanding not just Ashkenazi Jewish history but the broader story of Jewish diaspora communities will only increase.
Notable Quotes
We need to push back the date of that bottleneck to before the time of the Chapelfield individuals. It's most likely to have been during the formation of Ashkenazi communities in the early Middle Ages.— Mark Thomas, evolutionary biologist at University College London
There's no such thing as an Ashkenazi Jewish genetic disease. It's just genetic diseases that are found at a higher frequency.— Mark Thomas
The Hearth Conversation Another angle on the story
Why does it matter when this genetic bottleneck happened? Isn't the fact of it what counts?
The timing tells you something crucial about how Ashkenazi communities formed. If the bottleneck happened in the early Middle Ages, it means the genetic concentration happened during the actual formation of Ashkenazi identity—not later, during some crisis. It changes the whole narrative.
But these people in the well—they were killed in a riot. How does that connect to genetics?
It doesn't directly. The massacre itself didn't cause the bottleneck. But the remains gave us a window into what the gene pool looked like in the 12th century. We could see the variants were already there, already concentrated. That's the evidence.
The article mentions they found signs of hard labor and malnutrition. Why include that detail?
Because it matters for how we understand medieval Jewish life. There's a stereotype of wealthy, protected Jewish communities. These bones show people who worked hard, who were undernourished. They were vulnerable. That's the human reality underneath the genetics.
So endogamy—marrying within the community—that's not a choice, it's just what happened?
It's both. In medieval Europe, Jews were often legally restricted, socially separated. Marrying within your community wasn't always a choice in the modern sense. Over time, that concentration of variants became part of the population's genetic signature.
What happens next with this research?
They're looking at more medieval Jewish remains from Germany. The database of ancient genomes keeps growing. Eventually, you'll have enough data to see the whole picture of how diaspora populations formed and changed. This one well in Norwich is just the beginning.