For the past 800 years, we’ve all blamed dirty, flea-infested rats for spreading the bubonic plague throughout Europe. But now a new study has revealed that these rodents may not have been to blame at all.
In fact, according to climate evidence from the time, it was probably gerbils - cute, innocent looking gerbils - that spread the Black Death.
I know, we were as shocked as you are. But in a new paper published in the Proceedings of the National Academy of Sciences, researchers from the University of Oslo in Norway looked back at climate data from the 14th century and found that it just wouldn’t have made sense for rats to have started the outbreak.
“For this, you would need warm summers, with not too much precipitation,” Nils Christian Stenseth, an author of the study, told Rebecca Morelle from the BBC. "We have looked at the broad spectrum of climatic indices, and there is no relationship between the appearance of plague and the weather.”
But curiously, there is a link between the climate in Asia and the spread of the Black Death, as well as the following plague outbreaks that recurred between the end of the 14th century and the 1800s - a period known as the "second plague pandemic".
To work this out, the researchers analysed 7,711 historical plague outbreaks, and compared them to historical climate data from 15 tree-ring records. What they found was that European plague outbreaks always followed a warm summer in central Asia that came after a wet spring.
Those conditions are pretty terrible for black rats, the researchers concluded, but for cute little Asian gerbils, it’s ideal.
They now believe that after these climate conditions, gerbils and their fleas, which were carrying the Yersinia pestis plague bacteria, hitched a ride to Europe with travellers along the Silk Road. And, like clockwork, a few years later, death and panic spread across the continent.
The discovery not only clears black rats for the original Black Death outbreak, but also the second plague pandemic, which resulted in the deaths of more than 100 million people across Europe up until the 1800s.
As Sarah Kaplan explains for The Washington Post: “[The findings] also explain why the disease popped up intermittently century after century, rather than lingering on the continent as long as rats were around to carry it.”
This isn’t the only new hypothesis for how the bubonic plague spread - last year, scientists examined plague DNA and found evidence that the disease was airborne, rather than spread via flea bites.
But the team is now hoping to analyse DNA from ancient European skeletons to back up their research. If they find that there were genetic changes over time, it would suggest that re-outbreaks of the plague were caused by new rodent arrivals (in the form of gerbils) rather than existing plague reservoirs living on the backs of black rats in Europe.
“If we’re right, we’ll have to rewrite that part of history,” Stenseth told the BBC.
Not only that - after eight centuries of blame we’ll have to absolve black rats for causing one of the worst epidemiological crises in history. After all they’ve done for us, we feel pretty bad about it, too.