The biggest-ever study into medieval Ashkenazi DNA has found that their ancestry was unexpectedly diverse. 

The study, published by the academic magazine Cell last week, says that Ashkenazi Jews received the majority of their genetic ancestry sources by the 1300s. It also concluded that there had been little change to the DNA markers of modern Ashkenazi populations.

This backs up a recent study on Jewish remains in Norwich which found that the medieval individuals discovered contained far more affinity with modern Ashkenazi genes than expected. 

The 47 graves which formed the study were located by German archaeologists in 2013 during the excavation of part of a medieval Jewish graveyard in Erfurt, Central Germany ahead of construction plans. The remains have since been reburied in the Thuringian capital’s 19th-century Jewish cemetery.

Co-author Dr David Reich of Harvard University said that their work, “provides a template for how a co-analysis of modern and ancient DNA data can shed light on the past. “Studies like this hold great promise not only for understanding Jewish history, but also that of any population.”

The DNA samples were derived from 38 individuals and through comparisons with modern Ashkenazi genomes the global research team concluded that the medieval Erfurt Jewish population “were noticeably more genetically diverse than modern Ashkenazi Jews,” wrote co-author Hebrew University Professor Shai Carmi.

Dr Carmi wrote that “closer inspection revealed that the Erfurt population was divided into two groups: one with more European ancestry compared to modern Ashkenazi Jews, and one with more Middle Eastern ancestry.”

The study, which has been three years in the making, found that the research also suggests that the “bottleneck” among the Ashkenazi population occurred up to a millennium before the Erfurt community's establishment in the late 1000s.

Erfurt

Erfurt's Alte Synagoge is one of the best preserved medieval synagogues in Europe. The city was home to a thriving medieval Jewish community until their expulsion in 1454 (Getty)

A “bottleneck” is when a sudden decrease in population size increases rare genetic variants in a given group, events widely thought to have impacted the genetic makeup of current Ashkenazi populations.

Dr Carmi explained that several of the genetic issues present in modern Ashkenazi populations, such as BRCA 1 mutations and Tay Sachs Disease, indicate a very small initial population, with pathogenic variants that were carried by the founders” eventually becoming widespread due to the tendency to marry others within the same community.

The group of scientists used radiocarbon dating on 10 dental samples, concluding that the remains indicated individuals who has all lived between around 1270 and 1400.

Investigation of their dental isotopes also found that not all of the individuals had drunk the same water from childhood, suggesting that several of them were immigrants.

The 47 graves included two families, including children buried close to their father who appears to have died following an injury to the skull. Dr Carmi said around eight of the 33 viable individual samples were genetically related and admitted that the small sample size could mean these findings are not representative of the whole community.

“As with other ancient DNA studies, our historical inferences are based on a single site in time and space. This implies that our data may not be representative of the full genetic diversity of early Ashkenazi Jewry, as we have indeed inferred,” the study explains.

The findings also suggest that “Medieval Ashkenazi Jews are best viewed not as a single homogeneous community (as it came to be at the present), but as an ‘archipelago’ of communities, differentially affected by founder events and mixture with local populations,” Dr Carmi outlined in an FAQ document prepared alongside the in-depth scientific study.

Studying Jewish remains is often difficult, given strict prohibitions regarding the disturbance of Jewish burial sites.

Dr Carmi said that he would ideally “relax much more the regulations on the studies of living people but regulate much more the study of ancient DNA.”

However the researchers stressed that they wished to avoid anything “unethical” and consulted with the local Jewish community and a rabbi before the study. Rabbinic authorities recommended that the research only use the unattached teeth of skeletons that have been exhumed rather than specifically extracting samples from bones.