Modeling the decline of religion

People claiming no religious affiliation constitute the fastest growing ``religious'' minority in many countries throughout the world.\footnote{Zuckerman, P. ``Atheism: Contemporary rates and patterns,'' in Cambridge Companion to Atheism, University of Cambridge Press, 2007.} Here we use a minimal model of competition between social groups\footnote{Abrams, D. M. and Strogatz, S.H. Modelling the dynamics of language death. Nature 424(6951), 900 (2003).} to explain historical data on the growth of religious non-affiliation in 85 regions around the world. We also describe numerical experiments that support the validity of the model. According to the model, for societies in which the perceived utility of not adhering is greater than the utility of adhering, religion will be driven toward extinction.