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Black Death Plague Shows Limited Ancestry, Immune Effects in Study of Ancient Cambridge

Arnold Böcklin: Die Pest (1889)

NEW YORK – New research suggests the Black Death pandemic alone may not have had pronounced effects on the genetic ancestry and immune capabilities of surviving individuals in the UK's Cambridgeshire region. 

"Although we observe major long-term changes in genetic ancestry, we were unable to detect a change in ancestry or genetic diversity between our pre- and post-Black Death cohorts to account for the hypothesized increased mobility after the Black Death caused by labor shortages," the authors wrote in Science Advances on Wednesday, noting that the "short time span of a few decades, small sample size, and relatively low genetic differentiation in central and eastern England would all make detecting short- to medium-range migration within England challenging."

With low-coverage genome sequencing on 275 representatives from 10 Late Medieval and post-Medieval archaeological sites in Cambridge and other parts of Cambridgeshire county, the researchers considered the host genetic consequences of the Black Death, a pandemic caused by the Yersinia pestis bacterial species that spanned nearly a decade, from 1345 to 1353.

The authors reasoned that the pandemic "could have posed selective pressure for better resistance to the plague," since it wiped out some 30 percent to 65 percent of individuals in affected parts of Europe.

Ancient individuals profiled for the study included inmates from a charitable hospital, who were buried in the hospital's cemetery, the team explained, along with members of a 13th-century Augustinian friary and individuals buried in large urban or rural gravesites.

The investigators noted that ancient individuals buried at the hospital and friary cemeteries were typically not related to one another, as would be expected, while other cemeteries considered tended to contain members of the same families.

In contrast to studies published in the past — which highlighted ancestry and immune gene shifts linked to plague-related migration and selective pressures — findings from the current analyses did not uncover genetic ancestry shifts that tracked with the pandemic.

Toomas Kivisild, a researcher with the University of Cambridge, the University of Tartu, and KU Leuven who led the current study, cautioned that the available data may not be sufficient for detecting post-plague migrations from locations in central, eastern, or southern England where modern-day reference populations have high levels of ancestral homogeneity.

Even so, the new analyses highlighted genetic ancestry changes related to other historical events affecting Medieval Cambridge — from a Late Medieval uptick in Danish and Dutch ancestry to post-Medieval mixing with populations from Scotland and Wales that tracked with known political and economic events, he explained. But they did not point to specific pre- and post-plague ancestry shifts.

"While Cambridge was a university town, it would not have been surprising for us to find individuals with exotic ancestry," Kivisild noted, "but the fact that we do not find them could be because many people who lived and worked in Cambridge may have died or been buried elsewhere."

Likewise, the team did not identify immune-related genetic changes in the individuals profiled post-plague despite an apparent rise in immune-related gene variant differentiation, arguing against the notion that the Black Death offered a major immunity boost to Europe's post-pandemic populations.

"[W]e find that variants in immunity genes are more differentiated than the small set of neutrally evolving variants they called from their low coverage data," Kivisild explained. "However, this signal disappears when we use a fuller range of neutrally evolving sites confirmed to be variable in high-quality modern data."

"Our study does not rule out the possibility that the Black Death influenced the frequency of certain immunity variants," he added, "but we need to do more work with bigger sample sizes from different locations to find out what they are and whether the same or different immune genes were affected by selection in different populations."