Black Death 700 Years Ago Affects Your Health Now

The terrible effects of the plague pandemic changed our genes in such a way that it still affects our health today, almost 700 years later.

When the Black Death hit Europe in the mid-1300s, it killed up to half of the population. A groundbreaking study that looked at the DNA of skeletons from hundreds of years ago found changes that helped people survive the plague.

But the same changes are linked to auto-immune diseases that people have now.

The Black Death was one of the most important, deadly, and sad times in history. Up to 200 million people are thought to have died. Researchers thought that something so big must have changed the way humans evolved. By looking at the DNA in the teeth of 206 ancient skeletons, they were able to tell for sure whether the bones were from before, during, or after the Black Death.

Black Death 700 Years Ago Affects Your Health Now
Black Death 700 Years Ago Affects Your Health Now

Bones from the East Smithfield plague pits in London, which were used for mass burials, were part of the study. Other samples came from Denmark. This researcher is looking at an old tooth that has DNA that has broken down.

The most important finding, which was published in Nature, was about changes in a gene called ERAP2. You were 40% more likely to live through the plague if you had the right mutations.

Professor Luis Barreiro from the University of Chicago told me, “That’s huge, it has a huge effect, and it’s surprising to find something like that in the human genome.”

The gene’s job is to make proteins that break apart invading microbes and show the immune system the pieces. This makes the immune system better able to recognize and destroy the enemy.

Black Death 700 Years Ago Affects Your Health Now

There are different versions of the gene, some of which work well and some of which don’t do anything. You get one copy from each parent. So the lucky ones, who were most likely to live, got one from their parents that worked well. And the people who lived had children, who passed on the helpful mutations to their children. This made them suddenly much more common.

Evolutionary geneticist Professor Hendrik Poinar from McMaster University told me, “It’s huge that we see a 10% change over two or three generations. This is the strongest selection event in humans to date. Experiments done in the present day with the plague bacterium (Yersinia pestis) confirmed the results.

People whose blood had the helpful mutations were better able to fight off the infection than those whose blood did not. Prof. Poinar said, “It’s like watching the Black Death happen in a petri dish. That’s very interesting.”

Even now, more mutations make people less likely to get sick than there were before the Black Death. The problem is that they have been linked to auto-immune diseases like Crohn’s, which helped keep your ancestors alive 700 years ago but could hurt your health now.

Other events in our past have left a mark on our genes. About 1% to 4% of modern human DNA comes from our ancestors who slept with Neanderthals, and this makes it harder for us to fight off diseases like Covid. Prof. Barreiro said, “This means that scars from the past still have a remarkable effect on how likely we are to get sick today.”

Prof. Barreiro said that the 40% survival advantage was the “strongest selective fitness effect ever estimated in humans.” It seems to be much more important than mutations that make people resistant to HIV or help them digest milk, but he warns that direct comparisons are hard.

The Covid pandemic, on the other hand, will not leave the same kind of legacy. Evolution happens when people can have children and pass on their genes. Covid mostly kills older people who are too old to have children anymore.

The fact that plague could kill people of all ages and in such large numbers is what made it so important.

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