THORNHILL WAS STEERED TOWARD the topic of the human psychological reaction to disease in the early 2000s by a young graduate student advisee named Corey Fincher. Fincher had arrived at the University of New Mexico intending to study the mating behavior of rattlesnakes. After a time, however, he became curious about the evolutionary effects of disease on human cultural behavior—and particularly about the question of why cultures tend to fall along a spectrum between societies that are liberal and value individual rights and freedoms and societies that are authoritarian and value group membership.
Fincher, Thornhill and their fellow social scientists talk about “collectivist societies” vs “individualist societies”, but their “collectivist” doesn’t mean communist or socialist, and “individualist” doesn’t mean libertarian. In plain English, what they are basically talking about is a conservative or right-wing view of the world vs. a liberal or left-wing perspective. In strongly collectivist societies, group membership forms the foundation of one’s identity. Adhering to the rules of family and kin and making sacrifices for the good of the group are expected. By contrast, in strongly individualist societies like those of the United Kingdom, the U.S., Australia, and the Netherlands, individual rights are valued above duties to others. One’s identity does not derive from the group, but rather is built through the individual’s personal actions and achievements.
Psychologists and other social scientists have long been curious about this robust difference between human populations. Although these differences have been confirmed by many cross-cultural studies in a variety of different ways, no one had come up with a convincing evolutionary theory to suggest why it would be advantageous for one group of people to value individual rights more than another. Were these outcomes just accidents of history?
Fincher suspected that many cultural values and political leanings might be masks for underlying behavioral immune responses. What if more xenophobic and ethnocentric cultures had developed certain tendencies as a group defense against foreign pathogens? A strong preference for in-group mating, for example, might help maintain a community’s hereditary immunities to local disease strains. Strict rules and punishments for non-monogamous mating could also limit disease vectors.
To test his hypothesis, Fincher set out to see whether places with heavier disease loads also tended toward authoritarian rules and group-first beliefs. Would a map of disease prevalence and one of conservative/collectivist cultures overlap?
Working with Damian Murray and Mark Schaller, two psychologists from the University of British Columbia, and Thornhill, Fincher compared existing databases that rated cultural groups on the individualist-collectivist spectrum with data collected from the Global Infectious Diseases and Epidemiology Network and other sources. The team paid special attention to nine pathogens (including malaria, leprosy, dengue, typhus, and tuberculosis) that are detrimental to human reproductive fitness.
Just as the researchers theorized, they found a strong correlation between collectivist values and places with high pathogen stress. The places in the world that had less disease to deal with were cultures that scored higher on individual rights and less restrictive sexual and social behavior.
![Individualism vs infectious disease rates](https://attentionfwd.com/wp-content/uploads/individualism-infectious-disease-1200x800-1-375x253.jpg?1611384591 375w 253h, https://attentionfwd.com/wp-content/uploads/individualism-infectious-disease-1200x800-1-575x388.jpg?1611384591 575w 388h, https://attentionfwd.com/wp-content/uploads/individualism-infectious-disease-1200x800-1-775x522.jpg?1611384591 775w 522h, https://attentionfwd.com/wp-content/uploads/individualism-infectious-disease-1200x800-1-1024x690.jpg?1611384591 1024w 690h, https://attentionfwd.com/wp-content/uploads/individualism-infectious-disease-1200x800-1.jpg?1611384591 1200w 809h)
View the original map from ResearchGate.net
During our interview at the zoo, Thornhill appeared neither boastful about his theory nor particularly defensive about criticism. At 69 years old, he is the picture of an avuncular, somewhat rumpled professor, happy to spin out his ideas. At this stage in his career, he said, he no longer spends time worrying that other social scientists are not yet on board or that they think he may be overreaching. He is fond of quoting Albert Einstein, who once said, “the grand aim of all sciences is to cover the greatest number of empirical facts by logical deduction from the smallest number of hypotheses or axioms.”
Of course, grand hypotheses can be easy to come up with: just eavesdrop outside any dorm-room door. Theories that actually explain broad patterns in nature, Thornhill acknowledges, are extremely rare. But he is convinced he has one of those extraordinary beasts by the tail. Other social scientists, he tells me, will eventually catch up.
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. Xenophobic 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. 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 eventual outcome.
Moreover, the liberalizing 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 like the World Health Organization’s 20-year campaign that finally eradicated smallpox in 1979, 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 liberal values is on your agenda, he says, health care and disease abatement should be your main concern.
If our pathogen stress reaction has truly been triggered by the pandemic, Trump is likely to benefit in the upcoming election. Indeed, it may be one reason he is currently president. Remember that the Zika virus arrived in the news just as Trump was telling his audiences that Mexican immigrants carry disease. It was a message that appeared to resonate with conservative voters.
With the world’s best and brightest on the case, chances are good that we will see a Covid-19 vaccine in the upcoming year. But the coronavirus will certainly not be the only pathogen threat we are likely to face. Higher temperatures, elevated sea levels, and increased precipitation in some areas—all associated with climate change—are expected to bring tropical diseases to higher latitudes and elevations in the coming decades. Pathogens that once perished in cold climates and dry soils may find newly congenial zones of heat and moisture, and new host populations. Incidents of dengue fever in the U.S., for example, are expected to spread beyond Hawaii and the Mexican borderlands as climate change expands the habitats of the mosquito that carries the virus. Unless effective health interventions ward off these new threats, humans in ever higher latitudes may again resort to their embedded psychological and cultural defenses. Collectivist group behaviors including xenophobia, traditionalism and conformity, may be due for a comeback.
![John's Hopkins Interactive Global COVID-19 map](https://attentionfwd.com/wp-content/uploads/johns-hopkins-covid-interactive-map-1536x893.png?1611384591 1536w 893h, https://attentionfwd.com/wp-content/uploads/johns-hopkins-covid-interactive-map-375x218.png?1611384591 375w 218h, https://attentionfwd.com/wp-content/uploads/johns-hopkins-covid-interactive-map-575x334.png?1611384591 575w 334h, https://attentionfwd.com/wp-content/uploads/johns-hopkins-covid-interactive-map-775x451.png?1611384591 775w 451h, https://attentionfwd.com/wp-content/uploads/johns-hopkins-covid-interactive-map-1024x595.png?1611384591 1024w 595h, https://attentionfwd.com/wp-content/uploads/johns-hopkins-covid-interactive-map-1300x756.png?1611384591 1300w 756h, https://attentionfwd.com/wp-content/uploads/johns-hopkins-covid-interactive-map-1700x989.png?1611384591 1700w 989h, https://attentionfwd.com/wp-content/uploads/johns-hopkins-covid-interactive-map.png?1611384591 2036w 1184h)
Map from Johns Hopkins Center for Systems Science and Engineering tracking the spread of COVID-19. View interactive map
ONCE YOU BECOME AWARE of the pathogen stress theory, it has a kind of earwormish power. Even the most obvious counterexamples that spring to mind can, on closer inspection, seem to offer oblique and even surprisingly overt support for some version of the pathogen stress theory. It’s rather conspicuous that Nazi Germany—probably the most famous modern example of an ethnocentric, bellicose, authoritarian regime—arose in a northern clime, and not in some tropical latitude. But consider that the Nazi party began its rise to power in the aftermath of the Spanish flu pandemic that had killed over two million people across Europe—over half a million in Germany alone. And remember that much of Hitler’s poisonous rhetoric specifically suggested that Jews were disease carriers. Again and again, his rants portrayed Germany as an organism fighting disease—caused, among other things, by “Jewish bacteria.” Did Hitler manage to manipulate an unknown psychological mechanism that had been triggered by the threat of disease in the German population?
There are several disquieting aspects to Fincher and Thornhill’s theory. Fincher is careful to say up front that their hypothesis is not meant to telegraph value judgments or guidance, but it’s hard not see the pathogen stress theory’s distinction between collectivist and individualist societies as a kind of politically charged world-history morality play.
When Thornhill talks about the culture in the South that he remembers from his childhood, he highlights the racism and xenophobia and tends to skip over many of the more positive aspects of collectivism, such as strong kinship networks, in-group generosity (a.k.a. “Southern hospitality”) and deep religious faith.
So, on one hand you have collectivist cultures rife with xenophobia, racism, adherence to authority, and restrictive religions. On the other side are liberal cultures that promote equality, open-mindedness, democracy, and the acceptance of outsiders. One set of cultural values is a psychological defense against sickness; the other, a logical outcome of life in a healthy society. In this light, the pathogen stress theory can seem to offer evolutionary justification for the cultural values that Thornhill and Fincher themselves espouse—a reminder, some might say, that not only history, but science as well, is written by the victors.
But for his part, Thornhill is confident in the evidence underlying his theory, and relatively untroubled by the implication that he is advocating an outcome. “If you increase health then people will become more liberal and happier,” he told me at the zoo. “I don’t think that is a bad idea.”
The pathogen stress theory is also hard to swallow in a way that evolutionary psychology arguments often are—especially for those who fancy the idea that we are in individual control of our thoughts, emotions, and behaviors. The next time someone tells you about their religious beliefs or their support for a conservative candidate, try convincing them their convictions spring from an unconscious disease-avoidance mechanism. Or, alternatively, try telling a liberal acquaintance that their left-leaning politics and values are only as deep as the good luck that has allowed them to live in a relatively disease-free zone.
“It is true that the pathogen stress theory doesn’t integrate with the profundity we feel when we talk about values,” Thornhill admitted while eating a sandwich at the zoo cafe, seemingly unconcerned with the small flock of pigeons pecking at food scraps around our table. “When we think about our religious or political beliefs we feel like we’ve decided on them. They don’t feel like a defense against disease. They feel like something more meaningful. They feel like the truth.”