LEILA FADEL, HOST:
Nearly 700 years ago, one of the biggest pandemics ever swept the globe. And now a recent study suggests that outbreak of bubonic plague may have helped protect future generations against disease. NPR's Michaeleen Doucleff has this story on the Black Death.
MICHAELEEN DOUCLEFF, BYLINE: In 1348, the bubonic plague arrived in London and hit the city extremely hard. Luis Barreiro is at the University of Chicago and is a co-author of the study. He says that so many people were dying so quickly that...
LUIS BARREIRO: There was no more place in the cemeteries. So what happened is that the king at the time bought this piece of land, and they start digging it.
DOUCLEFF: This land turned into a mass grave with hundreds of bodies, some stacked five deep. In the end, the Black Death killed up to 50% of people in parts of Europe and the U.K. That's a mortality rate that's nearly 1,000 times larger than what we've had during COVID.
BARREIRO: And we just went through this pandemic, right?
DOUCLEFF: Yeah.
BARREIRO: And we all think that it was insane. And, like, it completely changed the world and our societies and all that, Now try to project - I mean, if it's even possible for you to try to project a scenario where 30-, 50% of the population dies.
DOUCLEFF: Barreiro is a human geneticist. And he wondered if the people in London who did survive the Black Death could have had some kind of advantage, perhaps something in their DNA, like a mutation that protected them. So he and his colleagues did something that almost seems like wizardry. They extracted DNA from the bodies buried at this mass cemetery and also from the bodies buried before and after the plague.
BARREIRO: We just wanted to see if we were able to identify particular mutations that would protect them against the agent that caused the Black Death.
DOUCLEFF: Turns out they hit the jackpot. They identified not one but four mutations that likely gave surviving Londoners an advantage. And the advantage was big. One mutation gave people a 40% advantage in terms of survival against the plague.
David Enard is an evolutionary biologist at the University of Arizona. He says that 40% is the biggest evolutionary advantage ever recorded in humans. And survivors, of course, passed on that advantage to their descendants.
DAVID ENARD: It's faster and stronger than anything we've seen before in the human genome. And it's really pushing the boundaries of what we thought was possible, so it is a pretty big deal.
DOUCLEFF: One of the mutations, in a gene called ERAP2, likely helped people clear out the plague infection quickly because it amps up the inflammatory response against the pathogen. This mutation has stuck around in the human genome for centuries, likely because it helps people fight off many pathogens.
ENARD: It's been advantageous to have them around for many other potential bacterial or even viral epidemics.
DOUCLEFF: But this mutation also comes at a cost. Maria Avila Arcos is a paleogeneticist at the National Autonomous University of Mexico. She says the mutation increases a person's risk of autoimmune diseases such as Crohn's.
MARIA AVILA ARCOS: If your immune system is, like, super strong, then that can also lead to autoimmune diseases.
DOUCLEFF: But the study, she says, has a big limitation. The Black Death struck Asia and parts of Africa. This study only tells us about a very small population of people, essentially northern Europeans, which greatly limits the scope of the findings.
AVILA ARCOS: There might be way more mechanisms. Like population could have had, like, way more cellular mechanisms to cope with this, like, devastating outbreak.
DOUCLEFF: And so the question is what other advantages might our genome have that could be helping to protect us against pandemics?
Michaeleen Doucleff, NPR News.
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