Krishnendu Halder/Reuters

Being a New Yorker, I'm something of a rat-spotter. And I'm an unsentimental one at that. The sight of a dead rat rarely rattles me, both because it's so familiar and because of the rodent’s reputation. Rats are gross—why mourn their loss?

But centuries after the bubonic plague besmirched their reputation, rats may have finally achieved a measure of redemption. A new study in the Proceedings of the National Academy of Sciences has shifted the blame for the Black Death to gerbils. The pandemic, which first erupted in the 14th century and resulted in millions of deaths in medieval Europe, was widely believed to have been caused by bacterium transported by fleas attached to black rats. Warm weather was thought to be connected with the blossoming of rat "reservoirs" and outbreaks of the plague on the continent.

But when researchers compared climate fluctuation in Europe with flare-ups of the plague, they didn't find a relationship between the outbreaks and the weather. Instead, the evidence pointed them to the weather in Central Asia—and to a less-maligned rodent: gerbils.

"We show that wherever there were good conditions for gerbils and fleas in Central Asia, some years later the bacteria shows up in harbor cities in Europe and then spreads across the continent,” Nils Christian Stenseth, a professor at the University of Oslo in Norway, told the BBC. He and his fellow researchers theorize that wet springs followed by warm summers in Asia served as a boon to gerbil populations, which then traveled to Europe, fleas and all, by way of the Silk Road commercial route. They're now hoping to test that theory by analyzing DNA from skeletons found in Europe.

Whatever the ultimate conclusions, the prospect of rats being exonerated for their most famous offense made the Humane Society’s John Hadidian giddy. The organization’s senior scientist has spent decades working to bridge the divide between man and rodent, and to counter the cruelty of the former. “We're not going to kill our way out of this problem,” he said by phone on Tuesday, soon after news of Gerbilgate had broken. Rat poison has proven damaging in urban and rural environments, Hadidian noted; a poisoned rat can lead to a poisoned mountain lion or even a dead house cat. He was hopeful that the Black Death study's findings might change people’s attitudes toward rats. “Anything that brings us to a better understanding and more tolerance is going to be a plus," he said.

It's not quite a tabula ratsa, but it's close. Unless you're into gerbils.

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