In 1348 The Black Death arrived in London, eventually killing up to half the population of Europe, North Africa, and the Middle East in the 14th century. That’s a mortality rate that’s nearly 1,000 times larger than what we’ve had during the COVID-19 pandemic. With so many people dying so quickly, cemeteries filled up and mass burial sites, referred to as ‘plague pits’, were built to accommodate the dead.
A human geneticist named Luis Barreiro 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. Barreiro and his colleagues did something that almost seems like wizardry. They extracted DNA from the bodies buried at the East Smithfield plague pit, and from two cemeteries that contained the remains of people unaffected by the plague, who died up to 50 years before or after the Black Death.
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. This is the biggest evolutionary advantage ever recorded in humans. And survivors, of course, passed on that advantage to their descendants.
One of the mutations, in a gene called ERAP2, likely helped people clear out the 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.
However, this evolutionary advantage came with a downside. Maria Avila Arcos, a paleogeneticist at NAU of Mexico, discovered that the same protective variants are linked to autoimmune diseases, such as Crohn’s disease, rheumatoid arthritis, and others. As in, if your immune system is super active then that can also lead to autoimmune diseases such as….you guessed…Addison’s disease.
This research shows how the Black Death helped shape human immune system evolution, trading infection resistance for increased autoimmune risk in modern populations. However, this study only tells us about a very small population of the world, essentially northern Europeans, which greatly limits the scope of the findings.
Submitted by Derek Clarke