A belief in the occult may have helped to stop the spread of dangerous infectious diseases throughout the course of human history, argues new research.

Pathogens are a serious threat to human health, and throughout the ages, people have developed strategies to manage their deadly effects, from vaccinations and quarantine to witch hunts and exorcisms. Writing in the journal Biological Sciences, a team of Australian researchers argues that believing in contagious supernatural forces may have helped to halt the spread of harmful contagions.

“A belief in contagious and contaminating evil forces – which we label ‘moral vitalism’ – would have provided a functionally equivalent framework for prediction and management, identifying both the infection and transmission profile of pathogens,” wrote the authors, adding that such a “suite of psychological responses” known as a “behavioral immune system” may have evolved to combat the serious threat of pathogens.

Moral vitalism may have been expressed as certain behaviors people would take in order to reduce their risk of interacting with those who were infected with an evil spirit, or disease. For example, a young girl who is delirious with a fever may have been thought to be possessed by the devil. Her household might have kept outsiders away for fear they too would become possessed, thus keeping them from becoming infected with the disease. This practice continued because it seemed to work; eliminating contact with an “infected” person helped to slow or stop the spread of “possession” (or disease).

“We examined how spiritual beliefs developed to explain and predict the devastating effects of pathogens and spread of infectious disease,” wrote the authors. To come to their conclusions, the researchers analyzed three separate studies, two of which examined archival data and a third multinational survey of more than 3,100 respondents. Across the three studies, the authors found a link between the belief of evil forces – evil eye, witchcraft, or the devil – and geographic variation in how common certain pathogens were found historically in some areas.

Higher levels of diseases in historical regions were found to be associated with stronger beliefs in the “the devil, the malevolent power of the evil eye and in witches who channel evil.” Conservative ideologies are also more prevalent in modern countries with high disease rates, such as shunning and restricting contact with the afflicted.

“We conclude that moral vitalism may be adaptive: by emphasizing concerns over contagion, it provided an explanatory model that enabled human groups to reduce rates of contagious disease,” noted the authors.

People turn to supernatural forces or spirits to explain events that are difficult to comprehend, whether they be biological or psychological. In societies, before germs were a thing, people would have used this to explain harmful events like disease outbreaks. We’ve seen such patterns on nearly every continent. Most notably, when the Black Death escalated across Europe, witch hunts ensued to blame whoever was possible for the devastating effects. They persist today when health issues are deemed “the will of God” or the “work of the Devil”.