Can the study of diseases explain how and why schisms take place in religion? Scientists say of course.
One of the first things you notice about what might be called religious epidemiology—studying religions with the same theories and formulas scientists use to study diseases—is how fraught the language is. People don’t adopt new religious ideas, they’re hosts who are infected by them. A new theology mutates from an old one, and works its way around a colonized community like a pathogen. It wins adherents because of selection pressures that drive evolution. Groups go to war or undergo a schism not for different gods or holy texts, but for xenophobic reasons, to avoid being contaminated.
Some of this fraught language is a matter of interpretation. The scientists studying religions are not theologians, obviously. They’re coming from their own fields, which have their own vocabularies, so they mean words like pathogen and mutate in a non-pejorative sense. Nevertheless, their microbe-inflected jargon hints that we’re in very different territory than the normal accounts of religious diversity.
Sometimes scientists use diseases as a metaphor for how religions evolve and change; in other cases, they believe diseases really do drive people apart and force them to adopt unique beliefs. Above all, these scientists want to sidestep any quirks of history and form universally applicable theories of how and why religions split.
Naturally, this can put them at odds with believers. Religious adherents in the middle of a schism don’t see themselves in any abstract model—to them, it’s a unique crisis. And to understand the crisis, they’d say you have to study the particular history and culture that led to it. But those are the very particulars scientists want to strip out—and need to strip out to make general sense of the problem.
Indeed, those two approaches—making theoretical models of religious movements and studying individual religions—are often incompatible, says Mark Chaves, a sociologist at Duke University who has studied schisms in the United States. “A major fork in the road in the scientific study of religion is whether you think of religion as a generic thing and try to create a theory of religion or whether you just observe religious diversity” as it manifests itself, he says.
But however much believers resist the reduction or abstraction of their beliefs, scientists won’t stop deploying models. What’s more, the resistance doesn’t mean the scientists aren’t correct in what they discover.
When Michael Doebeli was growing up in Switzerland, he didn’t much think about it. Once he began studying biology, it nagged him. In the 1500s in Europe, Catholics and what now are known as Protestants underwent a major schism. Then the Protestants themselves split a number of times in turn, leaving the former religious unity of Europe shattered. Sociologically, economically, and politically the split made sense. But from the perspective of evolutionary biology, it didn’t, says Doebeli, now a joint professor in the zoology and mathematics departments at the University of British Columbia.
Usually, he knew, religious beliefs diverge because of isolation. Two groups of people that lack a common culture and that live in widely removed areas will naturally conclude different things about god, morality, creation, and the metaphysical underpinnings of the universe. But in Europe in the 1500s, people were not widely separated—it was easy to move between countries—and they all shared a common religious culture, one based in the Vatican. “It wasn’t like people went to some remote island and changed their beliefs and came back,” says Doebeli. “All the people were Catholic before they were Protestant.”
Given that geographical and doctrinal closeness, the splitting of the Roman Catholic Church offended Doebeli’s sensibilities as a biologist. So he and a colleague, Iaroslav Ispolatov, decided to poke around for an underlying evolutionary cause.
That’s not to say Doebeli thought there was some sort of Darwinian, survival-of-the-fittest state in Europe back then. Instead, he simply borrowed theories and equations from genetics and population biology. But instead of studying how slightly different genes get passed from generation to generation, he decided to study how slightly different religious ideas, or “memes,” get passed from person to person within a culture.
He found first of all that, just as with genes, if religious memes are too similar, the culture stagnated—no religious diversity emerged. Easy enough. But if there were different religious ideas floating around, and provided that the memes were not too easy or difficult to accept, then schisms could occur. A new and possibly heretical idea would make its way through the population, would stick to and stay with some people, and those people would branch off from the rest because of it. Eventually, both the infected and non-infected would coexist as distinct “species.”
What’s more—and here’s the mathematical part, the real science—sometimes memes split and mutate quickly at first, when the ideas they represent are fresh, but then stagnate and settle down again into very stable lines (left: People start off at the bottom with similar religious ideas, but over time they diverge and form their own sects. The white areas have the highest concentration of people, while the grey, fringe areas have fewer.). Other times, the memes continue splitting and splitting. Historically, the former case resembles the Great Schism in Christianity around 900, when two distinct but stable lines, the Roman Catholic and Eastern Orthodox Churches emerged. The latter case resembles what happened to the Protestant movement starting in the 1500s and continuing through today, with new sects emerging all the time.
Epidemiology enters this model because genes, germs, and memes of religious ideas all seem to spread through societies in the same way. Indeed, the notion that ideas spread like germs has been a popular area of study lately. To adopt a few phrases, if a fashion can reach “a tipping point” where it’s suddenly inescapable, there’s no fundamental reason a religious tenet cannot “go viral” and infect thousands of new believers in the same way.
Overall, this model was exciting because Doebeli no longer needed to look for geographic isolation or some sort of cataclysm to explain why religions split. As long as ideas were spreading and mutating, religious speciation was natural, even inevitable. In fact, the charts and graphs Doebeli produced with his models, full of branches and twigs, could just as easily pass for a biological tree of life as for a schematic diagram of the various divisions and reunifications that Christian churches have faced throughout their histories.
The big question, naturally, is what causes religious schisms in the first place. And here’s where the scientific models lag. Doebeli cheerfully admits he has no idea what drives believers apart. His main concern was just to see if population biology could come close to modeling religious diversity.
He did need something to ignite schisms, though. And partly because it was easy to represent mathematically, he assumed that the rate of religious defection depended on the number of current believers. That is, he assumed large groups lost more members to offshoots and sects than small groups; and the larger the group got, the higher the rate of defection. When the number of defectors reached a critical mass, the religion was considered split.
Doebeli didn’t think his model was totally unrealistic, but he did fear an anthropologist might find such an assumption “naïve.” Actually, though, this notion does parallel one classic view of how religions break apart. In that model, explains Chaves, the Duke sociologist, churches often splinter because of discord between the social classes.
In any human organization, religion being no exception, a hierarchy emerges and people will move into leadership roles after a certain number of members join. A bureaucracy usually emerges, too. Eventually, the lower classes in the hierarchy will grow unhappy and rebel. And if their demands are not met, they will split off to revert to a “truer” form of the original religion. Doebeli’s guess that large groups splinter more quickly resembles the classic view because the larger a group gets, the more likely an elite will emerge, and the more power the elite will have.
Still, as a biologist, Doebeli tends to favor biology-based explanations. He does think that the immense size and power of the Catholic Church in Europe in the 1500s made it unwieldy and corrupt—driving people away to Luther, Calvin, and others. But he also thinks in terms of carving out evolutionary niches: Two species (or sects) can most easily thrive together, he says, when they target different ideas and play different roles
in society.
“Evolutionarily,” he says, “your success depends on having different traits than others. If a religion becomes very common, there are too many people doing the same thing.” Such a state will lead to competition, “and that’s bad for a bigger proportion of people.” Adopting a new religion is therefore a survival tactic in the social environment.
In the future, Doebeli plans to talk with more social scientists and figure out other variables besides group size that might cause splinters. “We’re really just getting started,” he says. What’s important is that his models of infective memes can accurately model religious evolution, even if he doesn’t quite know what
drives them.
Corey Fincher, on the other hand, does think he knows what drives the diversification of religion. Whereas Doebeli uses infection and the spreading of diseases more as a model or metaphor for religious schisms, Fincher believes diseases actually do splinter religions.
It seems far-fetched at first—even experts in religious diversification seem baffled when they hear of this idea. But Fincher bases his ideas on solid evidence, and while he may not have ironclad proof, his reasoning makes a lot of sense step by step.
His first observation is that the northern latitudes and the equatorial, tropical regions of the earth are very different environments, both ecologically and culturally. Most importantly, the tropics show far more diversity than other parts. Ecologically, this translates into an abundance of plants, animals, fungi, and microbes. As a result, humans living in the lower latitudes are exposed to far more diseases.
Says Fincher, “the tropical habitat of being wet and warm and never really freezing is just great for parasites.” That wet, warm weather also allows insects like mosquitoes to thrive, which act as vectors to transmit diseases. Overall, he says, “the entire package of disease stress is greater in the tropics. And disease morbidity is much higher.” (The exception to a higher prevalence of disease in the tropics is sexually transmitted diseases, which appear all over the globe, wherever humans are having sex.)
Cultural diversity, including religious diversity, is also higher in the tropics. Norway and Canada, for instance, have about a dozen religions each, and even those don’t differ too much in the details. But Cote d’Ivorie in Africa—roughly the size of Norway—has 76 religions, and Brazil—roughly the size of Canada—a whopping 159. The most famous example is tiny Papua New Guinea, probably the most culturally diverse place on earth, with dozens if not hundreds of traditional religions. Missionary work last century left much of that country nominally Christian, but even then it’s a wild mix of indigenous customs with Christian theology and rituals. What’s more, no one church dominates the demographics. Religions are intensely local, with various sects confined to their parcel of land.
Those two types of diversity, ecological and religious, could be a coincidence. (Correlation does not imply causation, after all.) What’s needed to link them is a plausible mechanism for how one drives the others—and Fincher and his colleague, Randy Thornhill, both biologists at the University of New Mexico, think they have one. As Fincher put it, “we emphasize xenophobic and ethnocentric psychology, which comes from diseases.”
That is, in places with lots of different microbes, strangers from even nearby lands probably have novel and possibly deadly diseases. So it makes sense to avoid them. It’s the story of measles and smallpox—which Europeans brought to the New World and which devastated the American Indian population—played out in thousands of smaller theaters. And when tribes shun their neighbors and keep to themselves, their cultures evolve along different tracks, giving rise to many, many different species of religious belief.
This evolution didn’t happen in colder climates, Fincher argues, because microbial diversity is much lower. Strangers there will have the same diseases, so there’s no exorbitant cost associated with meeting strangers. That constant contact with others and constant flow of ideas between cultures, tend to keep them more homogeneous in all areas, including language, diet, and dress. (And in fact, Papua New Guinea is the richest linguistic region in the world, with hundreds of recognized language groups. Africa, too, tends to support many, many languages spoken by smaller groups of people.) At a base level, then, the variety of diseases in the tropics simply imposes isolation on native groups, and it’s the geographic isolation that leads to cultural diversity generally and religious diversity specifically.
Overall, while Doebeli’s meme theory seems to apply better to freely flowing populations and can help explain large, nation-wide schisms (even if it remains a little vague on the details), Fincher’s analysis provides an excellent way to study small-scale schisms, even if it might be powerless to explain a doozy, like why Catholics and Protestants split.
What’s more, even though it relies on evolutionary theory, Fincher’s disease-diversity hypothesis runs counter to one important notion about the co-evolution of humans and microbes—that the more diseases a population is exposed to, the better off it will be in the long run. Not every disease ravishes a population like smallpox did; and constant exposure to new threats generally strengthens people’s immune systems. There’s even good medical evidence that people can subconsciously “smell,” via pheromones, whether a stranger has resistance to different diseases than themselves.
According to this theory, we can detect whether others have a markedly different “major histocompatibility complex.” The MHC is a protein that resides on the surface of cells; when people are naturally immune to microbes, it’s often because the microbe cannot find a place on the MHC to latch onto. If two people from different tribes, each immune to a different set of diseases, have a child, the child will inherit an MHC profile that provides resistance to both sets of diseases. It will therefore be more likely to survive. Incidentally, this unconscious detection of MHC-related chemicals—which waft out of our armpits—helps explains why many people find exotic men or women so attractive. It also explains why human beings universally find siblings unattractive sexually, since siblings have an identical MHC profile.
MHC detection falls under what’s known as outbreeding—exposing yourself to lots of diseases, as opposed to inbreeding and shunning contact with new diseases. And while outbreeding is a very powerful idea in immunology, Fincher thinks it cannot explain everything about a population’s resistance to microbes. “We’re suggesting a spin on that,” he says, a golden mean. Though generally beneficial, “outbreeding has costs as well. You’ve got to have your diversification, but you may also need to inbreed.”
Despite all the clever science going into a theory like Fincher’s, it does seem to have one snag, one reason to hesitate. Namely, the people involved in a religious schism obviously wouldn’t cite disease as the reason for splitting off from another group. Normally they would appeal to theological or ethnic differences instead. In their minds, they adopt different religious beliefs not because a different tribe might make them sick, but because of a recent war, or because the other tribes’ gods are evil, or because every summer solstice those people downriver sacrifice an animal that’s considered sacred. In essence, the disease-diversity theory reduces people to automatons. Moreover, it is directly opposed to classic views of people splitting off into different religions because of repression or to revitalize a supposedly corrupted version of faith.
Then again, as Fincher points out, “People don’t need to be aware of the underlying reasons for groups to be splitting.” He compared it to falling in love with someone. “You may be attracted to someone—but not necessarily because you’re aware you’ll have great reproductive success mating with attractive people.”
Such explanations of how people love can come off a little sterile and unsatisfying, as they strip out much of the mystery. That doesn’t mean they’re incorrect. And so too with religious schisms: People can always rationalize breaking off into a new sect, but that doesn’t mean they’re right about their real reasons for doing so.
Still, social scientists who study religion tend to feel more troubled about dismissing people’s motivations. “A huge challenge in the behavioral sciences is to figure out the relationship between what people say about their behavior and what they actually do,” says Harvey Whitehouse, an anthropologist at Oxford University who has done field world on religious diversity in Papua New Guinea. “It’s not that what people say is wrong, it’s that it’s often a poor guide to people’s implicit beliefs.”
So how do social scientists explain schisms? For his part, Whitehouse advocates a multi-layered theory. He first explains that religions generally fall into one of two categories. Some hold their rituals infrequently, but those rituals produce a high degree of arousal, and others hold rituals frequently but produce only a low degree of arousal each time. Either one can capture and hold people, but they do so in different ways. (The other possibilities, high-frequency, high-arousal or low-frequency, low-arousal rituals, tend to burn people out or not sustain their attention.)
The infrequent but arousing rituals—like initiation rites (left) or fasts or drug-induced visions, all of which can be terrifying—came first in human history, Whitehouse says, and people built their religions around them for tens of thousands of years. “If you perform your rituals rarely, they have to have a deep psychological impact. If you don’t have high levels of arousal, the rituals don’t deliver enough punch psychologically for people to ruminate on.”
The downside is that people have to be present to partake in the rituals, so religions have to stay local. And even if religions do arouse people, “everyone’s ruminations are likely to be different,” Whitehouse said, “and you don’t have regular forums to check what everyone’s believing.” Overall, he added, “These sorts of rituals didn’t allow for very widespread dissemination. It was a source of tremendous diversity.” Hence the proliferation of local cults all over the ancient world.
About nine thousand years ago, two things happened. Some religions began to adopt high-frequency but low-arousal rituals. This leads to “a more standardized body of ideas,” Whitehouse said. In addition, literacy began to spread across the world, and with literacy came the emergence of an elite religious caste to promulgate and interpret that standardized body of beliefs. It’s unclear which came first, the literacy or the increase in ritual frequency (Whitehouse thinks the latter), but by about six thousand years ago, both were the norm in many parts of the world.
Religious standardization actually tended to suppress schisms for a long time, since people no longer had the freedom to brood on and interpret rituals subjectively. (And had much less reason to do so, since the rituals were less intense.) But that process can only go so far. As in Papua New Guinea, people may nominally belong to one religion, even with their practices remain distinct. And that seems to be happening today, Whitehouse noted. “We see a squeezing out of traditional religions, but behind these big labels like Christianity, Hinduism, Islam, there are a huge diversity of subgroups, hundreds of smaller variants.”
This is something that Chaves, the Duke sociologist, also noticed when he studied schisms in American Protestantism between 1890 and 1980. During those ninety years, he said that regardless of outside circumstances—wars, depressions, boom times, Prohibition, whatever—about two sects would split off from mainline line denominations every single year, and it never rose or fell much higher or lower.
Ironically, but probably inevitably, Chaves said that one major impetus for groups to splinter was efforts to consolidate them. Usually church leaders would try to force a rebellious group to reorganize, or accept some controversial tenet—a modern example might be the ordination of openly homosexual ministers. “Any time there are attempts at consolidation, someone will emerge from that a winner and someone will lose,” Chaves says.
Losers tend to pack up and defiantly start their own sects, reminiscent of Henry VIII’s England seceding from the Catholic Church over divorce. And there’s really no way around this, Chaves noted. “You might think at the end of the day that if you start with two groups and try to consolidate, you’ll end up with one. But really, if you start off with two and try to consolidate, you’ll end up with three.”
Chaves’s work is more descriptive and historical than Doebeli or Fincher’s scientific theories of religious evolution. And while he says he finds such scientific theories intriguing, it’s only up to a point. The big question, he says, is “Is there historical continuity?” That is, even if, say, microbes caused religious diversity in the pre-historical past, does that mean they’re still doing so today? “When I’m thinking about what explains why we have religious diversity [in modern times], it’s got to be these sort of social, cultural, and political processes.”
Nevertheless, scientists like Doebeli and Fincher won’t stop pursuing their scientific models for emerging religions. That’s because the evolutionary understanding of religion, says Fincher, “is a very powerful scientific approach [with] lots of theoretical apparatus behind it.” He says he’s gotten great feedback from people in the religious studies community, since few people had applied evolution specifically to schisms.
Though an anthropologist, Whitehouse counts himself among the fans of the strictly scientific approach. Of the different models he has seen, “What excites me in general are the ones that are really theoretically driven and therefore testable,” testability being a sine non qua of real science.
Still, he doubts if such testable theories will be any good before human beings have a deeper, clearer, and more scientific understanding of how the brain works: how memes arise and stick in people’s minds, how religious beliefs function, and so on. He also adds that scientists need to move away looking for “the magic-bullet, single explanation for religion. Religion comprises a lot of different traits—the afterlife, the efficacy of ritual, belief in supernatural agency—and the explanation for each of those components is going to be quite different. It’s a trap people always seem to fall into.”
If that’s the case, perhaps the best thing that could happen to those scientists studying the diversification of religion would be for them to have a few schisms of their own.
Sam Kean is associate editor of Search.
