Study: How Does the Black Death Still Affect Health 700 Years Later?

A study published Wednesday in the journal Nature suggests that our medieval ancestors may have passed on to us the genes that once helped them survive the plague of the Black Death, only today those genes make us more susceptible to certain diseases .

The study analyzed the DNA of centuries-old skeletons and found the mutations that helped people survive the plague that swept through Europe and killed at least 200 million people. However, the same mutations are associated with autoimmune diseases such as Crohn’s disease, rheumatoid arthritis and lupus.

These diseases direct the immune system, which is responsible for defending our body against disease and infection, onto us and begin attacking the body’s healthy tissues. “Having an overactive immune system might have been great in the past, but it might not be that helpful in today’s environment,” said Hendrik Poinar, an anthropology professor at McMaster University in Ontario and senior author of the study.

The Black Death was the single deadliest event in human history, the plague that swept across Europe, the Middle East and North Africa and by the 14th century had wiped out up to 50% of the population. Researchers theorized that seismic events must have affected human evolution. Therefore, this study shows how germs shape us over time, the researchers said.

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“Our current genome is a reflection of our entire evolutionary history,” said Luis Barreiro, a senior author of research related to our adaptability to different germs over time. He and his colleagues from the University of Chicago, Ontario’s McMaster University and the Pasteur Institute in Paris examined the ancient DNA of at least 200 people from London and Denmark.

The bone samples, specifically the teeth selected for this study, were from people who died over 100 years before, during and after the Black Death. Specimens were collected from the East Smithfield plague pits in London, used for mass burials in 1348 and 1349, and some others from Denmark.

The scientists were able to identify four genes that, depending on the variant, either protect against the pathogens of bubonic plague or increase their susceptibility.

The results were confirmed using the plague bacterium Yersinia pestis, and blood samples were taken from people who showed the helpful mutations resisted infection better than those without, a media report said.
So if a person had the right mutation, their chance of surviving the plague, which is mainly transmitted through the bite of an infected flea, was 40% higher, the study found. Today, these plague-resistant mutations are more common than before the Black Death.

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While previous research has attempted to examine the Black Death’s impact on the human genome, this study demonstrates the importance the plague had in the development of the human immune system, Barreiro said. Additionally, he added, it is a unique aspect of this research to focus on a narrow time window around the event.

However, the more recent Covid-19 pandemic will not leave a similar legacy in human evolution, the lead author said, attributing this to the much lower mortality rate compared to the Black Death.

Additionally, Covid was killing more elderly people who already had children or who were past the point, Barreiro said. While evolution works through a person’s ability to reproduce and pass on the genes, and since bubonic plague has killed so many across the age spectrum, it has had a huge impact, he added.

(With contributions from agencies)