Dr Corey Fincher and Prof Randy Thornhill of the University of New Mexico, Albuquerque, come to this conclusion after studying why religions are far more numerous in the tropics compared with the temperate areas.
"Why does Cote d'Ivoire have 76 religions while Norway has 13, and why does Brazil have 159 religions while Canada has 15 even though in both comparisons the countries are similar in size?" they ask.
The reason is that religion helps to divide people and reduce the spread of diseases, which are more common the hotter the country, the research suggests.
Ok, I have to get hold of the published paper. Somewhere here there seems to be a causation/correalation problem, but I'll comment on it after seeing the paper. In the mean time, here is their prediction and test:
Any society that increased its coherence by adopting a religion, and dealt less with local groups with other beliefs as a result of cultural isolation, gained an advantage in being less likely to pick up diseases from its neighbours, and in the longer term to have a slightly different genetic makeup that may offer protective effects, for instance by making them less susceptible to a virus.
Equally, societies where infectious diseases are more common are less likely to migrate and disperse, not because of the effects of disease itself but as a behaviour that has evolved over time.
" If this argument is correct then, across the globe, religion diversity should correlate positively with infectious disease diversity," they say.
And the team finds evidence to back this.
"A sample of traditional societies shows that the range of those societies is lower in areas with more disease agents, compared with areas with few pathogens, and in countries religion diversity is positively related to two measures of stress caused by infection with parasites. Religion richness was positively related to disease richness (and significantly so)."
As predicted, "we found that religion diversity is the highest where disease diversity is also the highest and the lowest where disease diversity is also the lowest. To our knowledge, previous evolutionary models do not offer an explanation for why religion diversity varies spatially across the globe.
But what about other competing socio-poltical forces affecting the growth of religious groups? Or non-religious factors leading to the segmentation of the population? I will get a copy of the paper and get on this.
Read the full story here. And of course, for more on origin of religions, check out David Sloan Wilson, as part of our Science & Religion lecture series at Hampshire College.