Thornhill and his colleagues made a prediction: that regions with a balkanized landscape of localized parasites would in turn display a balkanized landscape of localized customs and conspicuous cultural differences among human populations—dialects, unique religious displays, distinctive art and music, and the like. While there is much more research to be done, early findings suggest that—particularly when it comes to the development of local languages and religions—pathogen stress does appear to spawn cultural diversity.
A set of more cautious researchers would likely have circled the wagons after unveiling their theory and concentrated on building a body of evidence to defend their early claims. Having a novel explanation for why some cultures are collectivist while others are individualist would probably guarantee one’s place in social science lore. Thornhill and Fincher, however, didn’t stop for a breath. By the time the two published a major paper in Behavioral and Brain Sciences in 2012, they had marshaled evidence that severe pathogen stress leads to high levels of civil and ethnic warfare, increased rates of homicide and child maltreatment, patriarchal family structures, and social restrictions regarding women’s sexual behavior. Moreover, these pathogen-avoidant collectivist tendencies, they wrote, coalesce over time into repressive and autocratic governmental systems. Want to understand the rise of fascism, dictatorship, and ethnocentric campaigns that dehumanize outsiders? Look to the prevalence of pathogen threats.
Over the years, scholars like William H. McNeill and Jared Diamond have argued that germs and geography exert an under-appreciated influence on the rise and fall of societies. But for Thornhill and Fincher, human psychological adaptations to the threat of disease are nothing less than the missing link in our understanding of culture—a fundamental key to our collective values that researchers and philosophers over human history have overlooked.
But in Thornhill and Fincher’s view, it’s not just the threat of infection that shapes culture. The absence of disease threats, they argue, creates a different set of cultural conditions that, taken together, are the necessary precursors to modernity. Collectivist values, despite their potential effectiveness at fencing out disease, come at a steep cost to the cultures that harbor them. As Thornhill explained to me, keeping strangers at arm’s length can limit trade and stymie a culture’s acquisition of useful new technologies, materials, and knowledge.
So, as humans moved into drier and colder and less disease-ridden climates, Thornhill says, they likely discarded their costly xenophobic disease-avoidant ways and became less beholden to tradition, more willing to trade with others, and more accepting of technological innovations. Instead of censuring the individual maverick thinker in the group, societies eventually came around to rewarding those who challenged convention. With those changes came the rise of wealth and the spread of education to a larger and larger segment of the population. The more educated the population, the more people demanded participation in their governments.
Democracies, premised upon the rights and freedoms of individuals, were the natural outcome.
Moreover, the democratizing effect of lowering disease threats, they argue, can happen quite quickly—even within a generation. Freedom House, an organization that tracks governments, civil liberties, voter participation, and equality around the globe, considers 46 percent of all countries to be “free” today, as opposed to just 29 percent in 1972. Thornhill points out that this rise coincided with an era in which major health interventions, including vaccine programs, the chlorination of drinking water, and efforts to reduce food-borne disease, became commonplace in many parts of the world. Thornhill is not shy about the implications. If promoting democracy and other liberal values is on your agenda, he says, health care and disease abatement should be your main concern.The Germ Theory of Democracy, Dictatorship, and All Your Most Cherished Beliefs (Pacific Standard)