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 outward behaviors that serve to ward off disease. ….humans likewise manifest such instinctual behaviors to avoid infection and illness. Some of these habits very much parallel those seen in other creatures..everyday life is full of small defensive moves against contamination, some motivated by feelings, like disgust, that arise without conscious reflection.
Our moment-to-moment psychological reactions to the threat of illness, they suggest, have a huge cumulative effect on culture…these deep interactions between local pathogens and human social evolution may explain many of the basic differences we observe between cultures. How does your culture behave toward strangers? What kind of government do you live under? Who are your sexual partners? What values do you share? All of these questions may mask a more fundamental one: What germs are you warding off?
The threat of disease is not uniform around the world. In general, higher, colder, and drier regions have fewer infectious diseases than warmer, wetter climates. To survive, people in this latter sort of terrain must withstand a higher degree of “pathogen stress.”…over time, the pathogen stress endemic to a place tends to steer a culture in distinct ways.
Research has long shown that people in tropical climates with high pathogen loads, for example, are more likely to develop a taste for spicy food, because certain compounds in these foods have antimicrobial properties. They are also prone to value physical attractiveness—a signal of health and “immunocompetence,” according to evolutionary theorists—more highly in mates than people living in cooler latitudes do….our behavioral immune systems—our group responses to local disease threats—play a decisive role in shaping our various political systems, religions, and shared moral views.
…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…striking at the root of infectious disease threats is by far the most effective form of social engineering available to any would-be reformer.
Psychologists and other social scientists have long been curious about this robust difference between human populations. In strongly collectivist societies, group membership forms the foundation of one’s identity. Sacrificing for the common good and maintaining harmonious ties with family and kin 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 personal actions and achievements. 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 become more collectivist and another group to become more individualist.
…many behaviors in collectivist cultures might be masks for behavioral immune responses. To take one key example, collectivist cultures tend to be both more xenophobic and more ethnocentric than individualist cultures. Keeping strangers away might be a valuable defense against foreign pathogens…a strong preference for in-group mating might help maintain a community’s hereditary immunities to local disease strains….places with heavier disease loads also tended toward these sorts of collectivist values…(there is) a strong correlation between collectivist values and places with high pathogen stress…found further evidence for the pathogen stress theory by looking at geographical regions that had not only severe disease stress but also a highly diverse patchwork of local pathogen populations. The critters that make us ill—not only the viruses and bacteria, but also the ticks, flies, and mosquitoes that spread them—are tiny and lack the ability to regulate their own heat as larger organisms do. They often flourish only in very narrow climatic zones, where they are adapted to certain temperature and moisture levels. As a result, pathogen threats can be highly localized. One study, for instance, found at least 124 genetically distinct strains of the parasite Leishmania braziliensis across Peru and Bolivia.
If you were to live in such a pathogenically diverse place, you and your family would likely develop a resistance or immunity to your local parasites. But that defense might be useless if you were to move in with a group just a short distance away—or if a stranger, carrying a foreign pathogen load, were to insinuate himself into your clan. In such places, then, it would be important for neighboring groups to be able to tell the difference between “us” and “them.”
…..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… early findings suggest that—particularly when it comes to the development of local languages and religions—pathogen stress does appear to spawn cultural diversity.
….. 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…coalesce over time into repressive and autocratic governmental systems. Want to understand the rise of fascism, dictatorship, and ethnocentric campaigns that dehumanize outsiders?
Over the last few years, an increasing number of papers from other social scientists have backed the theory. While many of these researchers work with the same large data sets and long timescales that Fincher and Thornhill study, others have figured out ways to tease out the behavioral immune response in real time, on a smaller scale. Schaller and his colleagues, for example, set up a test to see if disease cues could influence laboratory subjects’ opinions of foreigners. Schaller’s team had one group of subjects watch a slideshow about germs and disease while another group watched a show about everyday accidents and dangers. The researchers then told the subjects that the Canadian government was going to spend money to attract immigrants to the country. As Schaller predicted, the test subjects who had been cued with the disease presentation were less inclined to spend money to attract people from unfamiliar countries.
..strong religiosity (may be) an adaptive response to pathogen stress…The most effective way to change political values from conservative to liberal…is through health-care interventions.
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.”…
…. 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…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.
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 a 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.”
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 control of our thoughts, emotions, and behaviors. …
Thornhill grew up in Alabama in the 1940s and ’50s. He says he witnessed firsthand the rank sexism, racism, 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 a hold 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 turned generations of Southerners 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.
‘…the bulk of evidence supports…If you lower disease threats in countries they become more liberal, and that is true for states in this country. The implication is that if you effectively target infectious diseases then you will liberalize the population.”