BY ETHAN WATTERS •
... What kind of government do you live under? Who are your sexual partners? How do you treat strangers? All of these questions may mask a more fundamental one: What germs are you warding off? ...
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. Our moment-to-moment psychological reactions to the threat of illness, they suggest, have a huge cumulative effect on culture.
Not only that—and here’s where [evolutionary biologist Randy] Thornhill’s theory really starts to fire the imagination—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.” Thornhill and his colleagues theorize that, 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.
Eh ... sex differences are being overlooked. Looking like Denzel Washington or David Robinson in West Africa is a good symptom that you have an excellent immune system, which you will hopefully leave to your children if you leave them nothing else. But looking like you're strong enough for a lifetime of hoeing the yam patch with the other mothers, because you can't expect that good looking, entertaining baby-daddy to do much providing, seems to be selected for in West African women. A strong back is not exactly what most people around the world visualize as "physical attractiveness" in women.
But the implications don’t stop there. According to the “pathogen stress theory of values,” the evolutionary case that Thornhill and his colleagues have put forward, 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.
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.
This seems more like a modern America list of Bad Things and Good Things with little regard for how they relate to actual backward cultures. Being Americans in 2014, we've been told over and over how Xenophobia Is Bad, so cultures that obviously have dysfunctions much be Xenophobic, right? Except ...
But, how about Japan? Healthy, long-lived, prosperous, low-crime, and xenophobic as all get out (just in their polite Japanese way).
In contrast, Africans, who suffer from a very high disease burden, are not terribly xenophobic. So, in colonial times, Africa was relatively easy for Europeans to conquer, especially as they got better at handling the disease burden. Opposition from Africans wasn't that huge of a problem for Europeans. Similarly, disease-ridden India was easy for Europeans to conquer.
Today, African countries routinely accept a million refugees from a civil war in a neighboring country. African tribes generally live much more intermingled with other tribes than in other parts of the world. Why? Until recently, most of Africa wasn't anywhere near it's Malthusian population density limits, so there wasn't all that much incentive to keep outsiders out. In general, Africans tended to worry about having too few people to protect against wild animals (which might explain why, while other cultures try to restrain sexual behavior, African culture generally tries to encourage it -- we need all the babies we can get.)
The real impact of high disease burden on African cultures was that it made urbanization difficult -- if too many people got too close together, the settlement could be wiped out by disease, so Africans tended to live in small villages spread out across the vast countryside, and seldom developed the specialized arts and crafts that urbanization allows.
What’s more, their work may offer a clear insight into how societies change. According to Thornhill’s findings, striking at the root of infectious disease threats is by far the most effective form of social engineering available to any would-be reformer.
Getting infectious diseases under control (e.g., Singapore v. Lagos) has all sorts of socially positive knock-on effects. Bill Gates puts lots of money into looking for a malaria vaccine because he understands this.
If you were looking for a paradigm-shifting theory about human behavior, step right up. “Once we started looking for evidence that pathogens shape culture,” Thornhill told me, “we began to find it in damn near every place we looked.”
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 instead 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 individualist and collectivist dispositions.
This isn't really all that good a spectrum for thinking about success and failure in the modern world. Sure, England is pretty individualist and it's a nice place to live, but then Japan is notably collectivist by temperament and it's not too awful a place, either. In contrast, perhaps the most individualist culture in the world is the Pashtuns of Afghanistan-Pakistan, who downgrade even loyalty within the nuclear family. A charming Pathan saying is:
When the floodwaters reach your chin, put your son beneath your feet.
And Afghanistan is an awful place.
Pacific Standard continues:
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.
Fincher suspected that 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.
Are Swedes more individualist or collectivist, more xenophobic or more ethnocentric? All of these concepts are extremely relativistic.
Keeping strangers away might be a valuable defense against foreign pathogens, Fincher thought.
Maybe. Andaman Islanders are very vulnerable to outside world diseases. The North Sentinel Andamans have stayed healthy, though, probably because they murder anybody who lands on their island.
And a strong preference for in-group mating might help maintain a community’s hereditary immunities to local disease strains. To test his hypothesis, Fincher set out to see whether places with heavier disease loads also tended toward these sorts of collectivist values.
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. What the team found was a strong correlation between collectivist values and places with high pathogen stress. In 2008, Fincher, Thornhill, Schaller, and Murray published a major paper in Proceedings of the Royal Society B that laid out the connection.
I critiqued one of these Thornhill papers in 2010.
Thornhill and Fincher 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.
Interesting; in general, however, the worst diseases are spread by mosquitos, rats, and other mobile carriers. That way they can kill you quick and still spread. Diseases that spread human tend to mutate toward mildness so you can still drag yourself into work and sneeze on your coworkers. Falciparum malaria, carried by one particular type of mosquito, is probably the most significant disease in the world in terms of Darwinian selection. The anopheles mosquito gets around on its own, so the notion of local germs that never move seems unpersuasive.
Super localized germs will tend to get milder because they are in a long term symbiotic relationship with their hosts. The big killers tend to sweep in from another continent, like the Black Death arriving from Asia in 1347 or smallpox in the New World after 1492.
However, germs that are transported from person to person not by the person but by a mosquito or similar mobile vector can remain virulent for a long time. Gregory Cochran's hypothesis from the 1990s is that falciparum malaria, which is worst in West Africa, is such a huge Darwinian selective force that it will tend to select for:
A. Immune systems resistant to malaria
B. Visible clues in males of resistance to malaria, such as being a Big Man
If a higher percentage of selection among West Africans is devoted to selecting for traits associated with malaria-resistance, then less selection in West Africans can be devoted to other kinds of useful traits. In contrast, if the Swedes or Japanese don't have to worry as much about infectious diseases, they can select more for other traits. That seems pretty persuasive, so you don't hear much about it. (David Epstein vaguely alluded to it in The Sports Gene.)
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.”
With that thought in mind, 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.
Perhaps, but causation could run the opposite way. Places where people don't get around much don't see much interchange of human pathogens.
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
And vice-versa -- the Spanish Flu of 1918 was spread in troop hospitals, and a lot of plagues in China seemed to follow the breakdown of public health measures during the breakdown of dynastic order.
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.
Eh, you know, highly disease prone tropical countries might pretend to have a a Grand Generalissimo with lots of shiny ribbons who makes all the decisions, but they actually tend to be lackadaisical and chaotic places.
Want to understand the rise of fascism, dictatorship, and ethnocentric campaigns that dehumanize outsiders? Look to the prevalence of pathogen threats.
Uh, no, not really. West Africa isn't much of a source of fascism.
Or it could be backwards: if you want to explain Nazis, note that disease burden in Germany was low and falling fast.