In the mid-13th century, a bacterial species spread by fleas and rats spread across Asia and Europe, causing fatal cases of bubonic plague. The “Black Death” is one of the most infamous pandemics in historical memory, and many experts estimate that it killed about 50 million Europeans, the majority of people across the continent.
“The data are sufficiently widespread and numerous to make it likely that the Black Death wiped out about 60 percent of Europe’s population,” wrote Ole Benedictow, a Norwegian historian and one of the leading experts on the plague, in 2005. When Dr. Benedictow published “The Complete Black Death” in 2021, he raised that estimate to 65 percent.
But those numbers, based on historical documents from the time, vastly overestimate the plague’s true toll, according to a study published Thursday. By analyzing ancient pollen deposits as markers of agricultural activity, researchers from Germany found that the Black Death created a patchwork of destruction. Some regions of Europe did indeed suffer devastating losses, but other regions remained stable and some even boomed.
“We can no longer say it killed half of Europe,” said Adam Izdebski, an environmental historian at the Max Planck Institute for the Science of Human History in Jena, Germany, and an author of the new study.
In the fourteenth century, most Europeans worked on farms, which required intensive labor to produce crops. If half of all Europeans had died between 1347 and 1352, agricultural activity would have declined.
“Half of the workforce disappears immediately,” said Dr. Izdebski. “You cannot keep land use at the same level. In many areas you would not be able to sustain it.”
The loss of half the population would have left many farms fallow. Without enough herders to tend the livestock, pastures would be overgrown. Shrubs and trees would have taken over, eventually replacing it with mature forests.
If the Black Death did indeed cause such a shift, Dr. Izdebski and his colleagues, they should be able to see it in the pollen species that survived the Middle Ages. Every year plants release huge amounts of pollen into the air, some of which ends up on the bottom of lakes and wetlands. Buried in the mud, the grains can sometimes survive for centuries.
To see what pollen had to say about the Black Death, Dr. Izdebski and colleagues found 261 sites across Europe — from Ireland and Spain in the west to Greece and Lithuania in the east — where grains were stored from around 1250 to 1450.
In some regions, such as Greece and central Italy, the pollen told a tale of devastation. Pollen from crops like wheat decreased. Faded dandelions and other flowers in meadows. Fast-growing trees such as birch appeared, followed by slow-growing trees such as oak.
But that was hardly the rule throughout Europe. In fact, only seven of the 21 regions the researchers studied underwent a catastrophic shift. In other places, the pollen registered little change.
In regions like Ireland, central Spain and Lithuania, the landscape even moved in the opposite direction. Pollen from mature forests became rarer, while pollen from grassland and farmland became even more common. In some cases, two adjacent regions turned in different directions, with the pollen suggesting that one went to the forest and the other to farms.
While these findings suggest that the Black Death wasn’t as catastrophic as many historians have claimed, the authors of the new study did not provide a new figure for the pandemic’s true toll. “We’d rather stick our necks out,” said Timothy Newfield, a disease historian at Georgetown University and one of Dr. Izdebski.
Some independent historians said the new, continent-wide study matched their own research on certain European sites. For example, Sharon DeWitte, a biological anthropologist at the University of South Carolina, has found that skeletal remains from London during that time period showed signs of a modest toll from the pandemic. That made her wonder if the same was true for other parts of Europe.
“It’s one thing to have a reasonable suspicion, and quite another to produce evidence, as these authors do,” said Dr. The White. “That’s really exciting.”
Joris Roosen, head of research at the Center for Social History of Limburg in the Netherlands, said the Black Death did not stand out in his own historical research of Belgium. dr. Roosen measured the toll of the Black Death by looking at the inheritance tax paid in a province called Hainaut. Deaths from bubonic plague did indeed cause a spike in estate taxes, but Dr. Roosen found that other outbreaks in later years caused spikes that were just as big or even bigger.
“You can follow that for three hundred years,” he said. “Each generation is essentially suffering from an outbreak of the plague.”
But other experts weren’t convinced by the new study’s findings. John Aberth, the author of “The Black Death: A New History of the Great Mortality,” said the study didn’t change his view that about half of Europeans across the continent died.
dr. Aberth said he doubted the plague could spare entire regions of Europe as it ravaged neighboring regions.
“They were strongly linked, even during the Middle Ages, through trade, travel, trade and migration,” said Dr. aberth. “That’s why I’m skeptical that entire regions could have escaped.”
dr. Aberth also wondered whether a region’s shift to pollen harvesting necessarily meant its population boomed. He speculated that humans may have been wiped out by the Black Death, only to be replaced by immigrants taking over the empty land.
“Immigration of newcomers to an area could have offset demographic losses,” said Dr. aberth.
dr. Izdebski acknowledged that at the time of the bubonic plague, people emigrated all over Europe. But he argued that their documented numbers were too small to replace half the population.
And he also noted that huge waves of migrants had to come from other parts of Europe that had also supposedly been swept away by the Black Death.
“If you need hundreds of thousands of people to get in, where would they come from if half the population everywhere died?” he asked.
Monica Green, an independent historian based in Phoenix, speculated that the Black Death could have been caused by two strains of the bacterium Yersinia pestis, which could have caused varying degrees of destruction. Yersinia DNA collected from medieval skeletons points to this possibility, she said.
In their research, Dr. Izdebski and his colleagues didn’t explore that possibility, but they did consider a number of other factors, including climate and population density in different parts of Europe. But none were responsible for the pattern they found.
“There’s no simple explanation behind that, or even a combination of simple explanations,” said Dr. Izdebski.
It is possible that the ecology of rats and fleas that spread the bacteria differed from country to country. The ships that brought Yersinia to Europe may have come to some ports at a bad time of year to spread the plague, and to others at a better time.
dr. Izdebski worked on the study amid the spread of another pandemic spanning multiple continents, and said there were lessons to be learned from the Black Death in the coronavirus era.
“What we’re showing is that there are a number of factors, and it’s not easy to predict from the outset which factors matter,” he said, referring to how viruses can spread. “You cannot assume that one mechanism will work the same everywhere.”
