From The Telegraph:
Prof Richard Dawkins the atheist and sceptic, has condemned religion as a “virus of the mind” but it seems that people became religious for good reason – actually to avoid infection by viruses and other diseases – according to a study published today in the Proceedings of the Royal Society, Biological Sciences. 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. 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.
More here.