© 2014 Wiley Periodicals, Inc. In so far as researchers viewed psychical, occult, and religious phenomena as both objectively verifiable and resistant to extant scientific explanations, their study posed thorny issues for experimental psychologists. Controversies over the study of psychical and occult phenomena at the Fourth Congress of International Psychology (Paris, 1900) and religious phenomena at the Sixth (Geneva, 1909) raise the question of why the latter was accepted as a legitimate object of study, whereas the former was not. Comparison of the Congresses suggests that those interested in the study of religion were willing to forego the quest for objective evidence and focus on experience, whereas those most invested in psychical research were not. The shift in focus did not overcome many of the methodological difficulties. Sub-specialization formalized distinctions between psychical, religious, and pathological phenomena; obscured similarities; and undercut the nascent comparative study of unusual experiences that had emerged at the early Congresses.

Norenzayan's effort to integrate genetic and cultural evolution is a welcome advance over previous efforts, as is the attention he devotes to different levels of analysis from cognitive mechanisms to large group interactions. The scope of Norenzayan's argument, however, is bound to leave many scholars of religion feeling uneasy. The content of his model, which is most likely over specified, will need further testing in light of historical evidence. Comparison of Big Gods with Robert Bellah's Religion in Human Evolution (2011) highlights some of the choices Norenzayan made in designing his model and suggests ways it could be elaborated. Historians of religion who would like to help test his model could keep an eye out for ‘watcher mechanisms’ that might play more of a role than ‘moralizing Big Gods’ in some traditions and, thus, potentially offer an alternative route to large, anonymous, yet stable groups.

Researchers have not yet done an adequate job of reverse engineering the complex cultural concepts of religion and spirituality in a way that allows scientists to operationalize component parts and historians of religion to consider how the component parts have been synthesized into larger socio-cultural wholes. Doing so involves two steps: (1) distinguishing between (a) the generic elements that structure definitions and (b) the specific features used to characterize the generic elements as “religious” or “sacred” and (2) disaggregating these specific features into more basic cognitive processes that scientists can operationalize and that historians can analyze in situ. Three more basic processes that interact on multiple levels are proposed: perceiving salience, assessing significance, and imagining hypothetical, counterfactual content.