Scientists no longer consider rats as the main proponent of the bubonic plague and have traced the "black death" to gerbils that came from Asia.
According to BBC News, authors of a study published in the journal Proceedings of the National Academy of Sciences believe weather records held the key to their discovery. Many scientists previously believed black rats and their fleas were responsible for introducing the bubonic plague to Europe in the mid-14th century.
Examining tree-ring records, the researchers wanted to know if the weather at the time of the various outbreaks would align with a rat-spread disease.
"For this, you would need warm summers, with not too much precipitation. Dry but not too dry," study co-author Nils Christian Stenseth, from the University of Oslo, told BBC News. "And we have looked at the broad spectrum of climatic indices, and there is no relationship between the appearance of plague and the weather.
"If we're right, we'll have to rewrite that part of history."
If a wet spring did give way to a warm summer, then the gerbil population in Asia would have thrived. At a time when the eastern and western hemispheres were trading, the gerbils would have transferred their fleas to European people and domestic animals as well.
"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," Stenseth told BBC News. "Such conditions are good for gerbils. It means a high gerbil population across huge areas and that is good for the plague.
"Suddenly we could sort out a problem. Why did we have these waves of plagues in Europe?
"We originally thought it was due to rats and climatic changes in Europe, but now we know it goes back to Central Asia."
