Christ the Redeemer statue in Rio de Janeiro. REUTERS/Ricardo Moraes

Where does the huge diversity of religious belief, which we so clearly see around the world, actually come from? The most obvious (and least controversial) answer is that it’s simply a function of cultural transmission -- in other words, ideas are passed on in families, but then spread from one group to another by factors ranging from interpersonal persuasion to military conquest.

A new paper in the Proceedings of the National Academy of Sciences, however, takes a radically different approach. The study -- by a multidisciplinary team of researchers from Australia, New Zealand, and Germany, as well as US researchers at several institutions -- suggests instead that the environment in which a culture or society emerges and lives may powerfully shape the kind of religion that it adopts. In other words, the paper suggests, there is a kind of geography of human religiosity -- one in which beliefs map onto the climates and ecology of different regions.

"It became very clear that there was a spatial pattern in the distribution of religious beliefs, and particularly the belief that there is some kind of deity that is involved in human morality," says Carlos Botero, the first author on the new study and an evolutionary ecologist at North Carolina State University.

The idea certainly makes theoretical sense, at least when you consider what recent research into the psychology of religion has found. These studies have often suggested that religion is a force that acts to bind human groups together, and that it acts more strongly when those groups are facing a lot of external challenges (environmental or otherwise). In one particularly striking example, a study in New Zealand showed a marked uptick in religiosity in the wake of a deadly earthquake, but only among people who were directly affected by the quake. In other research, meanwhile, making people think about death and randomness seems to promote more religious responses. Other past research has emphasized how religion serves to enforce social, group oriented behavior: For instance, one study found that people give more money away in an economic game if they are subtly made to think about God or religion before playing.

But it’s one thing to postulate that religion is a way to bind us together in threatening environments -- and quite another to demonstrate it. To do so, Botero and his colleagues turned to a classic anthropological source, the Ethnographic Atlas, a compilation of research on a large variety of traditional societies across the world compiled in the earlier part of the 20th century. The study examined the religious beliefs recorded for 583 of these societies, and correlated these beliefs with a host of ecological factors specific to the regions in which the groups live or lived, with a particular emphasis on environmental factors affecting climatic stability (the regularity of rainfall, for instance, or predictable temperatures) and the availability of resources (such as the abundance of plants, amphibians, and mammals).

Sure enough, they authors found that cultures who believed in a moralizing god or gods -- supreme beings who were believed to be involved in the fate of humans and who offered moral prescriptions on how to behave -- tended to be located in environments that were harsher to deal with and less climatically stable. "The bottom line is that we find both resource scarcity and the propensity to be exposed to ecological duress tends to be associated with these beliefs," says Botero -- presumably because in harsh environments, groups need to cohere and cooperate, and a shared belief in a moralizing god helps them to do that.

Here's one figure from the study, in which traditional societies with a belief in "moralizing high gods" (blue dots) and societies that are either atheistic or believe in spirits or non-moralizing deities (red dots) are plotted against the availability of one particular kind of natural resource, the potential for plant growth (gray shading). Note that the dots below do not reflect the religions that are currently practiced within these regions; rather, each reflects a traditional society, identified by anthropologists working in the early 20th century:

From Carlos A. Botero et al, "The ecology of religious beliefs," Proceedings of the National Academy of Sciences, November 10, 2014.

The researchers emphasize that their findings should not be taken as a form of geographical determinism. In addition to the environment and ecology, their model also took into account factors like language, a society's political complexity, and whether it practiced agriculture and animal husbandry. And the upshot is that "after you control for all that stuff, you find that ecology still has an effect," says Botero. Indeed, taking all of the relevant factors into consideration (not just ecology), the study was able to predict what kinds of religious beliefs a culture would show with 91 percent accuracy.

The latest paper overlaps fascinatingly with another recent body of research. Michelle Gelfand of the University of Maryland, College Park and her colleagues have demonstrated that both in the United States and across the world, societies that have historically been subject to more mortal threats -- like disease, natural disasters and wars -- tend to be more "tight," or intolerant of deviant behavior and outsiders. Cultures who have had an easier geographical shake, so to speak, tend to be more "loose," or laid back about norms and behavior. While Gelfand's work looked at a broader range of threats, the current research clearly suggests that  environmental challenges or dangers have a similar effect on a culture's embrace of moralizing norms, and the religious beliefs that may enforce them.

Granted, many will find it controversial that researchers are now trying to explain our personal religious belief systems as a function of geography, ecology, and the complexion of threats that different regions have faced. But Botero emphasizes that the research team included a religious studies scholar, and "tried to be extremely sensitive to the ways in which people perceive any kind of discussion of religion. And we think this is a nice example of how science and religion can actually live together and explore joint interests without any animosity."