The project, funded by an ERC Synergy Grant, aims to explain how pathogens shaped societies in pre-industrial Europe.

“Our bodies tell stories; especially the teeth of people living in past centuries are time capsules; we can read the DNA fragments they contain, including those belonging to pathogens,” said lead researcher Professor Adam Izdebski, a historian and ecologist who specializes in epidemics of the Middle Ages and early modern period.

The research will focus on 56 epidemics across 11 European regions, from Spain and England to Greece and Lithuania.

“We would have liked more, but there was not enough money! Seriously, we need significant cultural, religious, geographic, and political diversity to be able to examine the factors associated with different epidemic patterns,” Izdebski said.

Each region will be studied by local historians to ensure depth and accuracy.

The team chose the years 1350–1800 because of the quality of available data. “This period is much better documented than earlier periods of intense, increased epidemic frequency in Europe, such as the first plague pandemic (5th–7th centuries CE).

“Especially from the 16th century onward, we have reliable and detailed demographic data that enable us to precisely assess both the mortality rate and the demographic structure of the societies studied. The same applies to economic data, such as prices,” Izdebski said.

He added that later periods were excluded due to major changes in pathogens, living conditions, and communication networks. “The period 1350–1800 therefore provides us with sufficiently similar, yet diverse, and well-documented examples of epidemics that will allow us to build a broader epidemiological and ecological theory,” he said.

A key part of the project involves analyzing DNA from human teeth, which can preserve pathogens present in the bloodstream at the time of death. “Our molars are a kind of time capsule; they contain remnants of the blood that circulates through our bodies at the moment of death… The teeth of people living in the past are such time capsules, and it is possible to read fragments of DNA contained within them, including the DNA of pathogens active in our bodies,” Izdebski said.

“Most of the DNA in such a tooth is bacteria active after burial. Only a small portion is the DNA of the person to whom the tooth belonged, and a minimal portion is the genetic material of bacteria, for example, the plague… Nevertheless, if this DNA is preserved, with sufficiently intensive ‘reading’ of the sample, it may even allow to fully reconstruct the pathogen’s DNA and study its evolution,” he added.

Identifying the exact pathogens responsible for past epidemics would represent a major shift in historical research. “Beyond the evolution of the pathogens themselves, the very fact that we will know which pathogen is behind a specific epidemic is almost revolutionary,” Izdebski said.

“Suddenly, we no longer rely on uncertain interpretations of the descriptions of disease symptoms by contemporary doctors or chroniclers, but simply know what organism we are dealing with. This fundamentally allows to focus our research, for example, on the history of everyday life. We stop searching in the dark, so to speak, but know what we should focus on,” he added.

The project will also consider environmental conditions, such as climate, agriculture, and biodiversity. “Also with respect to other pathogens, we need to know how severe the winter was, how wet the spring was, whether the previous year’s weather was so extreme that a famine occurred, or perhaps the plague bacteria were brought into the city during a heatwave,” Izdebski explained.

Landscape reconstructions will allow researchers to compare agricultural intensity and biodiversity with epidemic patterns. “Our current research in some parts of Europe suggests that the Black Death (1346–1353 CE) – leading to the collapse of the agricultural model developed in Carolingian times – may have ended the period of optimal biodiversity in the post-glacial history of our continent,” he said.

Isotopic analyses of bones and teeth will provide further context by reconstructing diets in different regions. “Our bodies synthesize bones and teeth from what we eat… Therefore, the isotopic composition of bones and teeth allows us to reconstruct with great accuracy the structure of our diet at different stages of life. We need this knowledge to determine whether different types of diets and eating habits could also be related to the course of the epidemic and the scale of the resulting mortality,” Izdebski said.

The ERC Synergy Grant funding marks only the second time a Polish institution has secured support on this scale. For Izdebski, the most important outcome would be surprising results. “I think the greatest success will be if, in the end, it turns out that our initial intuitions were completely wrong, and the world – or rather, the segment of it we will study – functions completely differently from we initially imagined!” he said.

Anna Mikołajczyk-Kłębek (PAP)

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