The same diseases that plague humanity may also drive one of the fundamental elements of human culture, a new study suggests. A statistical analysis shows an association between higher rates of infectious disease and religious diversity around the world. The findings have already sparked debate within the academic community; critics are questioning the validity of the interpretation, and supporters say that the finding could offer a new perspective on why religions exist and what role they play in society.
The histories of individual religions are well-documented, but the evolution of religion itself is not well-understood. Two schools of thought have dominated the debate. The first views religion as a "byproduct" of other evolutionary adaptations such as larger brains. The second sees religion itself as adaptive, arguing that its role in social cohesiveness and other traits may have helped humans survive.
Corey Fincher, a biologist at the University of New Mexico, Albuquerque, falls into the second camp. Religion marks group members, he says, and can dissuade people from interacting with those outside the group. In areas with rampant infectious disease, this can be an advantage: No outsiders means no outside pathogens. Isolation can also prevent the exchange of ideas, or religions, in this case. That might lead to the rise of many independent religious systems.
Fincher and his colleagues looked for an association between a nation's religious diversity and rate of disease. They used Barrett's World Christian Encyclopedia to tally the number of religions in 219 countries and checked that against pervasiveness of disease in those areas, as documented in a global epidemiology database. There was a statistically significant, positive relationship between prevalence of disease and religious diversity, or religion richness. This persisted even when the researchers controlled for other variables that could impact the number of religions in a country: land area, population, religious freedom, and economic inequality. To correct for different patterns of human settlement in different parts of the world, they also tested the association of disease and religious diversity within the world's six major regions; the correlation still held true.
The results, published online yesterday by the Proceedings of the Royal Society B, offer a new answer to the question of why religions exist, Fincher says. "Religions may be for marking, but at a more fundamental level, social marking may in and of itself be due to infectious disease stress."
But Courtney Bender, a sociologist of religion at Columbia University, disagrees. Religions around the planet range from being very open to very closed to outsiders, she says: "You can't just say religions have strong boundaries." Indeed, traditional religious societies often interact with those outside their own group for trade or military alliances, says Richard Sosis, an evolutionary biologist at the University of Connecticut (U Conn), Storrs. Still, Sosis welcomes the study as a "great first step" in explaining religious diversity.
"I think [the researchers] are introducing an area that has been absent in the evolution of religion studies and is potentially an important one," says anthropologist Candace Alcorta, also of the U Conn. Alcorta notes that the existence of great empires in tropical, disease-rich areas--such as the Maya in the Yucatán Peninsula--seems to fly in the face of Fincher's findings. But the questions the study raises could inspire research that will move the field forward, she says.