With Trump’s poll numbers slumping, as you’d expect given the Administration’s management of the Covid crisis, Democrat pols think they can see a clearer path to victory. But they might be blindsided again in November, this time by a force more primal and powerful than logic or economics.
In 2017, I researched and wrote about “pathogen stress theory,” a concept that might help make sense of our cultural reaction to the pandemic. Several prominent evolutionary psychologists, most notably Randy Thornhill of the University of New Mexico, believe that our instinct-level reactions to the threat of disease shape many of our group behaviors and cultural beliefs. The theory boils down to this: societies located in regions that have more disease-causing germs have evolved with behaviors like tribalism, authoritarianism and xenophobia to serve as culture-wide defense mechanisms, while cultures located in regions with a lower level of pathogen threat are able to emphasize individual rights and cultural diversity.
How does your culture behave toward outsiders? Is your government more authoritarian or more democratic? How strict are your cultural rules about sexual behavior? What values do you share? All of these questions may depend on a more fundamental one: What germs is your culture warding off?
Until recently, a common criticism of pathogen stress theory was that it had little relevance to our modern era — global pandemics seemed like a boogeyman that belonged to the history books. Despite scary outbreaks of SARS, H1N1, and Ebola in recent decades, science’s ongoing campaign against viral and bacterial contagions had largely been a victory march.
But suddenly, in the year 2020, Earth’s 7.8 billion inhabitants find themselves simultaneously experiencing a historically high level of pathogen stress.
With Covid-19 burning its insidious path through populations and their economies, politicians around the world have begun using the pandemic to stoke xenophopic sentiment. Prime Minister Viktor Orban of Hungary has chosen to use the global coronavirus to implement anti-immigrant policies, suspend parliamentary oversight and rule by decree. Israeli Prime Minister Benjamin Netanyahu has used the pandemic as the reason for increasing surveillance powers and for postponing his corruption trial. Prime Minister Prayuth Chan-ocha of Thailand has imposed curfews and claimed the power to censor the news media.
“Leaders across the globe are invoking executive powers and seizing virtually dictatorial authority with scant resistance,” wrote investigative reporter Selam Gebrekidan in a column in the New York Times, “. . . And there are few sunset provisions to ensure that the powers will be rescinded once the threat passes.”
In the U.S., confederate flags have begun to pop up across the country, surprisingly as far north as Michigan, at protests fueled by President Trump’s tweets encouraging citizens to “liberate” states from their governors’ shelter-in-place orders. Could Covid-19 be the trigger that releases a pent-up burst of electoral energy still simmering in the ashes of the Old South? If Thornhill is right, it could.
To gain a better understanding of pathogen stress theory, I flew to Albuquerque and invited Thornhill to meet me at the local zoo. We were standing in front of the gorilla enclosure as he began to explain pathogen stress theory, when Mashudu, a 10-year-old western lowland gorilla, decided to help illustrate a point. In a very deliberate way, Mashudu sauntered over to the deep cement ravine at the front of his enclosure, perched his rear end over the edge, and did his morning business.
Had Mashudu, I wondered, just displayed what evolutionary theorists call a “behavioral immune response”—a concept central to Thornhill’s big theory? “Pooping downhill is pretty smart,” Thornhill said in agreement. “He got his waste as far away from him as possible. I think that would probably count as a disease avoidance behavior.”
It might seem strange to fixate on how a gorilla goes about answering the call of nature. But according to Thornhill’s hypothesis, much of what we humans like to think of as politics, morality, and culture is motivated by the same subconscious instinct that likely drove Mashudu to perch over that ledge.
Anyone with a basic grasp of biology knows that all animals have immune systems that battle pathogens—be they viruses, bacteria, parasites, or fungi—on the cellular level. And it’s also fairly well understood that animals sometimes exhibit overt behaviors that serve to ward off disease. At the most quotidian level, Thornhill finds it easy to convince people that humans likewise manifest such instinctual behaviors to avoid infection and illness.
Upon examination, everyday life is full of small defensive moves against contamination, some motivated by feelings, like disgust, that arise without conscious reflection. When you open the door of a gas station bathroom only to decide you can hold it for a few more miles, or when you switch seats to put as much distance as possible between yourself and a person who is coughing and sneezing in a waiting room, you are displaying a behavioral immune response. The arrival of the coronavirus has reminded us all that disease avoidant behavior and visceral emotions often go together. Someone openly sneezing or even touching their face can instantly bring on feelings of anger, disgust and even nausea.
But these individual responses are just the tip of the iceberg, according to Thornhill and a growing camp of evolutionary theorists. Our moment-to-moment psychological reactions to the threat of illness, they suggest, can have a huge cumulative effect on culture over time.
Not only that—and here’s where Thornhill’s theory really starts to fire the imagination—these deep interactions between local pathogens and human social evolution may explain many of the fundamental differences we observe between cultures. According to the “pathogen stress theory of values,”—our group responses to local disease threats—play a decisive role in shaping our various political systems, sexual behavior, religious beliefs, and shared moral views.
If they are right, Thornhill and his colleagues may be on their way to unlocking some of the most stubborn mysteries of human behavior. Their theory may help explain why authoritarian governments tend to persist in certain latitudes while democracies rise in others; why some cultures are xenophobic and others are relatively open to strangers; why certain peoples value equality and individuality while others prize hierarchical structures and strict adherence to tradition. What’s more, their work may offer a clear insight into how societies change.
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.
Historical prevalence of Infectious diseases
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 enforcing monogamy and restricting women’s sexual behavior.
Moreover, these pathogen-avoidant collectivist tendencies, they wrote, coalesce over time into autocratic governmental systems. Want to understand the rise of fascism, dictatorship, and ethnocentric campaigns that dehumanize outsiders? Look to the historical prevalence of pathogen threats in that culture.
Over the years, scholars like Jared Diamond and William H. McNeill have argued that the geography of germs exerts an under-appreciated influence on the rise and fall of societies. 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.
And here’s where Thornhill and Fincher’s once-obscure theory might unveil a hidden driver of the primeval forces dividing Red America and Blue America. While the U.S. scores high on the “individualistic” side of the spectrum compared to most other countries, we are also a country with something of a split personality. Northern states, which tend to be both colder and dryer, are more liberal than Southern states, which carry a much higher disease load. Infectious diseases like whooping cough and salmonella remain more common in the south where an individual’s life expectancy can be a decade lower than other parts of the country.
Thornhill grew up in Alabama in the 1940s and ’50s and has given a lot of thought to this dichotomy. He says he witnessed firsthand the rank racism, sexism and xenophobia that was rampant in the South during that period. And he is well acquainted with the region’s strong family ties and firm religious beliefs.
But he is also aware of a somewhat lesser known set of facts about his native soil. Around the time of his childhood, Southern states were finally getting the upper hand on a pair of diseases that had long plagued the region: malaria and hookworm. These diseases, writes Peter Hotez, the founding dean of the National School of Tropical Medicine at Baylor University, had historically turned many in the South into “anemic, weak, and unproductive children and adults.” Not surprisingly, Thornhill believes that the collectivism of the old South—the adherence to tradition, ethnocentrism, and suspicion of outsiders that marked his childhood—stemmed from its historically high pathogen load.
Similarly, he attributes the progress he’s seen toward a more egalitarian South to the alleviation of the region’s most pernicious health problems.
“You still hear people say that the old South will rise again, but I doubt it has a chance unless disease prevalence goes up dramatically,” he told me in 2017. “Maybe if you knock out all the sewage treatment plants and stop giving antibiotics to sick kids, it would have a chance.”
Of course, Thornhill’s apocalyptic scenario for what it would take for the US to move radically to the right, was conjured long before the arrival of Covid-19. The United States — indeed the whole world — has just recently embarked on a natural experiment to test Thornhill and Fincher’s pathogen stress theory. The outcome of the upcoming election might be in the balance.
If you increase health then people will become more liberal and happier, I don’t think that is a bad idea.
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.
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.”