Monday, January 30, 2023

DNA from 14thC teeth unravels mixed origin of Ashkenazi Jews

DNA from teeth unearthed in Central Germany has revealed the dual origin of Ashkenazi Jews in two distinct genetic, cultural and linguistic medieval communities.

The study, which is the largest analysis of medieval Jewish DNA, advances our understanding of the evolution of Europe’s Jewish communities and shows that rates of conversion of local Europeans to Judaism varied significantly at different locations and times.

With the permission of Thuringia’s Jewish community, a team of over 30 scientists obtained teeth for sampling from the remains of 33 people buried in the old Jewish cemetery at Erfurt. The medieval Jewish community of the city — which lay on an important east-west trade route — existed from the late 11th century to 1454, with a five-year gap following a devastating pogrom in 1349. It was one of the largest Jewish communities in Germany and its synagogue is the oldest complete synagogue in Central Europe.

The excavation at the medieval Jewish cemetery of Erfurt. Photo: Ronny Krause, Thüingischen Landesamtes für Denkmalpflege und Archäologie (TLDA)

For their study, published in Cell, the researchers obtained DNA from extracted teeth of 19 females and 14 males, aged 5-60, who probably lived in the 14th century. A cause of death could be determined for only one individual who was killed by several blows to the head. After analysing the DNA, the researchers found that the Jews of medieval Erfurt were considerably more genetically diverse than modern Ashkenazi Jews — the name, from the Hebrew Ashkenaz, given to Jews of Central and Eastern European origin who comprise about half of all Jews living today.

Professor Shai Carmi, a population geneticist at the Hebrew University of Jerusalem and one of the study’s authors, said: “When you look at the genomes of Ashkenazi Jews today, they are very similar to one another. Whereas in the Middle Ages we see this heterogeneity that we didn’t know about. We knew the population was culturally and linguistically heterogenous at the time. Now we know there was also genetic diversity, with two distinct groups, one of which had mixed with local populations from Central or Eastern Europe. This is an exciting finding that reveals something about the Jewish population that was not known before.”

The Old Synagogue of the medieval Jewish community of Erfurt. It is one of the oldest still intact synagogues in Europe, and is now serving as a museum documenting Jewish life in Erfurt. Photo: Shai Carmi

Both groups identified by the researchers had a mixture of ancestry from Southern Europe and the Middle East that suggests their remote ancestors lived in the Mediterranean world. Although there were strong affinities between both groups and modern Ashkenazi Jews, one group had a higher proportion of Middle Eastern ancestry than today’s Ashkenazim. The other had — in addition to Southern European and Middle Eastern ancestry — a significant amount of Eastern European ancestry, averaging 33 per cent. This group had a larger proportion of European ancestry than modern Ashkenazi Jews.

Isotope analysis confirmed that individuals from the two groups originated in different regions, drinking water with different chemical signatures. Nevertheless, people from the two groups were buried side by side in the cemetery, suggesting that there was no social segregation.

The large structure behind the excavation is a granary that was built in the 15th century on top of the cemetery. Photo: Martin Sowa, TLDA

The scientists suggest that the group with the higher proportion of Middle Eastern ancestry had origins in the Rhineland, where Ashkenazi Jews emerged as a distinct ethno-religious and cultural group in the 10th century. The other group appears to have had recent origins in Central and Eastern Europe and may be related to the historically recorded migration of families from Bohemia, Moravia, and Silesia into the Erfurt community after the Pogrom of 1349. According to this reconstruction, the “Rhineland” or Western group would have spoken German dialects while the Jews from the east spoke Slavic languages such as Old Czech.

Carmi said: “Both the Rhineland cluster and the Eastern European cluster seem to have had the same origin, but then they split. We don’t know when or where they split. If we have additional DNA samples from other sites, or new technical methods, in future, that could be very informative.”

Regarding their earlier ancestry, the Levantine and Southern European DNA of both groups could be consistent with them descending from Jews from Judea and the Eastern Mediterranean who settled in Italy and married local converts to Judaism over multiple generations before migrating north. However, the team stressed that there was not enough evidence to draw solid conclusions about this earlier period. Carmi said: “We can’t be confident about the precise proportion of Middle Eastern ancestry even though this is a historically interesting question, because we lack enough data on the ancient populations of the region.”

The study indicates that modern Ashkenazi Jews — whose DNA is more homogenous than the medieval community of Erfurt’s — are descended from both groups seen at Erfurt in approximately equal proportions. The researchers said this was consistent with studies of names, dialects, and religious rites that suggest that Western and Eastern Ashkenazi communities eventually merged to form a single culture.

Modern studies have shown that at least one major “bottleneck” must have occurred in the ancestry of Ashkenazi Jews. This means the Jewish population was so small over numerous generations that genetic variants increasing the risk of certain diseases that were randomly carried by one of the ancestors increased quickly, in numbers of carriers, once the population started growing. The data from Erfurt corroborates a recent study looking at the DNA of medieval Jews from Norwich, England, in showing that the bottleneck began early in the history of Ashkenazi Jews, about 1,000 years ago.

Among the signals of this bottleneck in the Erfurt remains, they found a variant in the BRCA1 gene associated with a higher risk of breast and ovarian cancer that is still more prevalent in Ashkenazi Jews today than in European non-Jews. At least eight of the Erfurt individuals carried mutations linked to diseases that are common in modern-day Ashkenazim.

A 14th-century Jewish wedding discovered in 1998, as part of the Erfurt Treasure hoard, depicted on postage stamps. Photo: Alamy

The Erfurt study indicates that most of the European ancestry of modern Ashkenazi Jews derives from admixture before the 1300s and conversion to Judaism was far more common in the medieval and ancient periods than later. Carmi said: “There was all this mixing happening wherever the Jews went for 2,000 years. However, the vast majority of it ended by the 14th century.”

It is unclear why mixing appears to have occurred in parts of Central and Eastern Europe when it was not common around the Rhineland, but, again, future studies may shed light on this.

The study took advantage of a rare opportunity because, under rabbinic law, the exhumation of bodies and disturbance of the dead are prohibited under almost all circumstances. However, when remains have already been unearthed as part of a rescue excavation, testing may be allowed.

After the expulsion of the Jews from Erfurt in 1454, a granary was built over the Jewish cemetery, outside the city walls. In 2013, the city permitted its conversion into a parking garage. This required the construction of a ramp and was preceded by a rescue excavation that found 47 burials with the legs facing Jerusalem, as per Jewish tradition. Before the skeletons were reburied in a 19th-century Jewish cemetery, the scientists obtained the samples for their study with the consent of the local Jewish authorities.

The history of Ashkenazi Jews involves a complex series of migrations linked to persecution and to shifting opportunities. During the medieval and early modern periods, many Jews from Germany settled in Poland and the territories of the Polish-Lithuanian Commonwealth. Later pogroms in Eastern Europe drove Ashkenazi migration back to Western and Central Europe and, subsequently, to the United States and Palestine. 

Following the Holocaust, involving the murder of about six million Jews, the majority of Ashkenazi Jews live in Israel and the US, with large communities in other countries including Britain and France.

The top image depicts Moses receiving the Law and is an example of medieval Jewish art from a Hebrew prayer book from Southern Germany, c. 1322, British Library Additional MS 22413. Photo: British Library.

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