Modularity, evolution and religious ontology. Should science study religion? In this paper I propose a way to understand the religious phenomena, based in its ontology, without excluding science, particularly cognitive sciences. Modularity of mind and evolutionary psychology can account for the origin of dualism and the teleology that underlies the minds that hosted religious beliefs. I will argue, from Dennett, Boyer and Dawkins naturalism, that religious phenomena is not a biological adaptation but a by-product of psychological mechanisms designed for another activities, such as the prediction of our and those of others behaviors, and the understanding of other living beings and natural phenomena. Key words: Modularity, evolution, cognition, adaptation, naturalization, religion.