Did the “Black Death” really kill half of Europe? New research says no.

In the mid-1300s, a species of bacteria spread by fleas and rats swept through Asia and Europe, causing fatal cases of bubonic plague. The ‘Black Death’ is one of the most notorious pandemics in historical memory, with many experts estimating that it killed around 50 million Europeans, the majority of people across the continent.

“The data is widespread and numerous enough to make it likely that the Black Death carried off around 60% of Europe’s population,” Ole Benedictow, a Norwegian historian and one of the leading experts on the plague, wrote in 2005. When Dr. Benedictow published “The Complete Black Death” in 2021, he raised that estimate to 65%.

But these figures, based on historical documents from the time, greatly overestimate the true toll of the plague, according to a study published Thursday. By analyzing ancient pollen deposits as markers of agricultural activity, German researchers found that the Black Death caused a mosaic of destruction. Some regions of Europe did indeed suffer devastating losses, but other regions remained stable, and some even exploded.

“We can no longer say that 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 author of the new study.

In the 14th century, most Europeans worked on farms, which required intensive labor to produce crops. If half of the Europeans died between 1347 and 1352, agricultural activity would have fallen.

“Half the workforce disappears instantly,” Dr. Izdebski said. “You can’t maintain the same level of land use. In many areas you would not be able to continue.

Losing half the population would have laid many farms fallow. Without enough shepherds to tend the cattle, the pastures would have become overgrown. Shrubs and trees would have taken over, eventually replaced by mature forests.

If the Black Death indeed caused such a change, Dr. Izdebski and his colleagues reasoned, they should be able to see it in pollen species that survived the Middle Ages. Each year, plants release large amounts of pollen into the air, and some ends up at 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 his colleagues selected 261 sites across Europe – from Ireland and Spain in the west to Greece and Lithuania in the east. ‘est – which contained grains preserved from about 1250 to 1450.

In some regions, such as Greece and central Italy, the pollen told a story of devastation. Pollen from crops like wheat has declined. Dandelions and other pasture flowers have withered. Fast-growing trees like birch appeared, followed by slow-growing ones like oaks.

But this was not the rule throughout Europe. In fact, only seven of the 21 regions studied by the researchers underwent catastrophic change. In other places, the pollen recorded little change.

In fact, in regions like Ireland, central Spain and Lithuania, the landscape has shifted in the opposite direction. Pollen from mature forests has become rarer, while pollen from pastures and farmlands has become even more common. In some cases, two neighboring regions deviated in different directions, with pollen suggesting that one turned towards the forest while the other turned towards the farms.

Although these results suggest that the Black Death was not as catastrophic as many historians have argued, the authors of the new study did not offer a new figure for the pandemic’s true toll. “We’re not comfortable showing our necks,” said Timothy Newfield, a disease historian at Georgetown University and one of Dr. Izdebski’s collaborators.

Some independent historians said the new continent-wide study was consistent with their own research into particular European locations. For example, Sharon DeWitte, a biological anthropologist at the University of South Carolina, found that skeletal remains from London during this period showed evidence of a modest toll from the pandemic. This led her to wonder if the same was true for other parts of Europe.

“It’s one thing to have reasonable suspicion, and quite another to produce evidence, as these authors do,” Dr. DeWitte said. “It’s really exciting.”

Joris Roosen, research director at the Limburg Center for Social History in the Netherlands, said the Black Death was indistinguishable from his own historical research on Belgium. Dr. Roosen measured the toll of the Black Death by looking at inheritance taxes paid in a province called Hainaut. Deaths from the bubonic plague did indeed cause inheritance tax to spike, but Dr. Roosen found that other outbreaks in later years created equally, if not larger, spikes.

“You can follow this for three hundred years,” he said. “Every generation, in essence, suffers from an epidemic of plague.”

But other experts were not convinced by the findings of the new study. John Aberth, the author of “The Black Death: A New History of Great Mortality”, said the study did not change his view that around half of Europeans across the continent died.

Dr Aberth said he doubted the plague could spare whole parts of Europe as it ravaged neighboring regions.

“They were strongly interconnected, even in the Middle Ages, through trade, travel, commerce and migration,” Dr Aberth said. “That’s why I’m skeptical that entire regions could have escaped.”

Dr. Aberth also wondered if a region’s shift to cultured pollen necessarily meant that the population there was booming. He speculated that people could have been wiped out by the Black Death to be replaced by immigrants taking over the empty land.

“The immigration of newcomers to an area could have compensated for population losses,” Dr Aberth said.

Dr Izdebski acknowledged that people were immigrating to Europe at the time of the bubonic plague. But he argued that their documented numbers were too small to replace half the population.

And he also noted that huge waves of migrants should have come from other parts of Europe which would also have been wiped out by the Black Death.

“If you need hundreds of thousands of people to come, where would they come from if everywhere half the population died?” He asked.

Monica Green, an independent historian based in Phoenix, has speculated that the Black Death could have been caused by two strains of the bacterium Yersinia pestis, which could have caused different levels of devastation. Yersinia DNA collected from medieval skeletons hints at that possibility, she said.

In their study, Dr. Izdebski and his colleagues did not examine this possibility, but did take into account a number of other factors, including climate and population density in different parts of Europe. But none explained the pattern they found.

“There is no simple explanation behind this, or even a combination of simple explanations,” Dr. Izdebski said.

It is possible that the ecology of rats and fleas that spread the bacteria is different from country to country. The ships that brought Yersinia to Europe may have come to some ports at the wrong time of year to spread the plague, and to others at a better time.

Working on the study during the spread of a different pandemic playing out across multiple continents, Dr Izdebski said there were lessons to be learned from the Black Death in the age of coronavirus.

“What we are showing is that there are a number of factors, and it is not easy to predict from the start which factors will be important,” he said, referring to how viruses can spread. “You can’t assume that a mechanism works the same way everywhere.”

Mary I. Bruner