TWH – A new study published in the journal Nature, examines the genetic mutations in European human populations that likely resulted from the bubonic plague. The study’s findings offer some interesting, and even tantalizing details when it comes to how the human species is capable of evolving.
The second recorded pandemic in history, courtesy of the bubonic plague caused by the bacterium, Yersinia pestis, resulted in the deaths of an estimated 30-50% of the human population in parts of Europe and the United Kingdom between 1347 and 1352.
Boccaccio’s ‘The plague of Florence in 1348’ – Image courtesy of Wellcome Images, operated by Wellcome Trust – Gallery: Wellcome Collection gallery (2018-03-24): CC-BY-4.0
Often referred to later in history as the “Black Death” due to the dark or blackened appearance of the skin that was the result of gangrene. The term “Black Death” was not used until around 1755, when it was translated from the Danish term den sorte død – “the black death.” During the outbreaks of the mid-14th century, it was referred to as “the pestilence,” “the great mortality,” or simply as “the plague,” depending on the region.
The social and economic impacts of the bubonic plague were immense since widespread death left entire villages abandoned, creating massive shortages in labor which resulted in the scarcity of food and other goods. Compared to the roughly 1% death rate of the current SARS-CoV-2 pandemic, it is hard to imagine a death rate of 30-50%.
When our collective ancestors are viewed through this lens of loss alone, it provides greater insight into their resilience and perseverance. Entire families were wiped out, travelers were often unwelcome and suspect, and food and other staples were increasingly hard to come by. Due to mass burials and cremations often conducted without the benefit of clergy and also due to person shortages resulting from death, there were the additional fears of not just a physical death, but a spiritual one.
The bubonic plague of the 14th century began in Asia and eventually made its way across Europe and into the U.K. in 1348. London saw so many deaths, so rapidly, causing cemeteries to become full that King Edward III purchased a plot of land that became a mass grave and ended up containing the bodies of over 700 plague victims.
Scanning electron micrograph of the Yersinia pestis bacterium found on the spines of a flea – Image credit: National Institutes of Health (NIH) – Public Domain
This mass grave in particular provided a fair-sized pool of DNA for researchers to pull from since they knew when all of the bodies were interred due to the city discontinuing the use of the cemetery once the outbreak had ended. This allowed them to compare the DNA of those who survived with those who did not.
They compared immune-related genes from 206 ancient DNA extracts from two different European populations sourced from three cemeteries in London and five locations across Denmark. What they found after they examined DNA from before, during, and after the bubonic plague outbreak was a total of 245 gene variants.
Of those variants, they identified four that possess elements that can help the human body survive exposure to Yersinia pestis. One variant, in particular, provided roughly a 40% increase in the chance of surviving the plague.
One of the things researchers found that surprised them was the speed at which these mutations occurred, in a matter of just a few decades. On the scale of evolutionary developments, this was blindingly fast. Similar human evolutionary mutations that have occurred, like the ability to tolerate lactose, took thousands of years to develop and were only minimally effective.
The other aspect of immunity the study has uncovered is that while the genetic variation that occurred allowed those possessing it a greater chance of survival when it comes to the plague, it also is likely to make them more susceptible to chronic inflammation and autoimmune disorders.
When the immune system responds robustly to kill off potential pathogens, it can also end up creating a chronic level of inflammation and result in autoimmune diseases, like multiple sclerosis and rheumatoid arthritis.
While the research is compelling, it is limited to just English and Danish populations making it hard to know how the genetic makeup of people in other regions of the world who experienced the bubonic plague may have mutated. At least for now.
What future research in this area might find when conducted on larger and more diverse populations is anyone’s guess. However, unless the most recent findings are anomalous and the reflection of an outlier, it seems logical that as a species, the systemic response in other regions might be similar.
So in addition to all the other things we can acknowledge as being bestowed upon us by our ancestors, the gift or curse of genetics when it comes to deadly diseases and autoimmune issues can be added to the list. While we may not be able to control which genetic traits we’ve inherited or exactly how they may manifest, every day we have the potential to learn more about how those who came before us not only endured but sometimes against all odds, managed to thrive.
In this season of the ancestors that is worth pondering and exploring, and celebrating.
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