According to a new study, black rats may be the victims of one of the animal kingdom's longest-running character assassinations.
Scientists studying the root causes of Europe's bubonic plague were surprised to learn that Asia's giant gerbil is the more likely villain behind the epidemic that wiped out 30 to 60 percent of the population. Researchers came to the conclusion after comparing tree-ring records with thousands of documented plague outbreaks in Europe. If rats were to blame, the beneficial weather supporting a rise in their populations would closely align.
"For this, you would need warm summers, with not too much precipitation. Dry but not too dry," professor Nils Christian Stenseth told the BBC. "And we have looked at the broad spectrum of climatic indices, and there is no relationship between the appearance of plague and the weather."
Instead, scientists found instances of the plague more closely followed weather patterns in Asia. Nearly every time the continent experienced a wet spring followed by a warm summer, the plague tended to make an appearance in Europe. Such weather is extremely favorable for another, more adorable, plague-carrying rodent: the Asian giant gerbil.
"We show that wherever there were good conditions for gerbils and fleas in central Asia, some years later the bacteria shows up in harbour cities in Europe and then spreads across the continent," Stenseth said.
While it's fun to think of these new villains as massive rodents several feet tall, the giant gerbils are only a bit larger than your common household pet variety, ranging from 6-8 inches in length. They are, however, extremely good at hosting and spreading disease.
The study says the gerbils likely hitched rides on caravans to Europe along the heavily traveled Silk Road, bringing with them the plague-ridden fleas that led to the eventual death of millions.
"We originally thought it was due to rats and climatic changes in Europe, but now we know it goes back to Central Asia," he said.
While rats may no longer carry the full blame for the plague, the researchers note that they still played a supporting role by "maintaining plague outbreaks on ships, as well as importing plagues into harbors."
Stenseth and his team will next fact-check their findings by analyzing DNA from several ancient European skeletons. If the genetic material reveals a large amount of variation in the type of plague, it will prove their theory that the pandemics were climate-driven and not solely from European rat populations.
You can review the full published study in the Proceedings of the National Academy of Sciences.
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