The evolutionary perspective on religion proposes that religious ideation is natural and plausible because of innate mechanisms, the product of evolution, that lead humans to imagine reality through egocentric, anthropocentric, animistic, or teleological processes and to interpret events through intentionality and design. If these mechanisms operate in all human brains, the level of religiosity in individual and social lives is likely to remain stable and uniform, regardless of time and place. Challenges to this perspective include that the expression of religious ideation is contingent on numerous conditions, contexts, and circumstances. Manifest individual differences in religiosity, and instability in collective religiosity, lead to consideration of the gap between “deep structure” and “phenotypic” manifestations. The most serious test of this perspective is the recent appearance of secularization, which entails a massive reduction in the resources devoted to religion. The chapter analyzes the challenges and provides an integration of historical and psychological data.