Norenzayan et al. make a compelling argument that cultural evolution has selected for beliefs and behaviors that increase group solidarity and reduce intragroup conflict. Over time, groups that had religious beliefs and behaviors that promoted intragroup prosociality had a competitive advantage over other groups. Prosocial religions also made it possible to increase group size through outsourcing third-party monitoring of exchanges to Big Gods.

As social networks have increased in size over human history, rituals have allowed groups to remain cohesive, while reducing the need for physical and social proximity. Rituals, which we define as socially stipulated, causally opaque group conventions (Legare & Souza Reference Legare and Souza2012; Reference Legare and Souza2014), are central to the cultural evolution of prosocial religions. The role of ritual in cultural evolution raises compelling questions about the process by which the elements of rituals were aggregated and honed to address the adaptive problems of group living. Here, we discuss how the social functions of ritual solve adaptive problems associated with group living. Ritual is a distinctly human predisposition – a psychologically prepared, culturally inherited, species-specific behavior. We propose that the evolution of ritual cognition builds upon selective social learning biases that may have become increasingly specialized for affiliative functions within social groups.

Engaging in rituals serves a variety of functions that solve adaptive problems associated with group living. First, rituals provide a means of identifying in-group members. Engaging in approved social etiquette and participation in group-specific ceremonies allow identification of in-group members, who are more likely to cooperate and less likely to free-ride than out-group members. Engaging in rituals also demonstrates commitment to in-group values. Rituals often include costly actions, in terms of time and energy expenditure as well as pain and sacrifice, that operate as reliable signals that convey commitment to the group. Individuals who demonstrate commitment to in-group values through ritual participation are more likely to be trusted in cooperative endeavors. Hence, rituals facilitate cooperation with social coalitions. Finally, rituals function as mechanisms of social group cohesion, which, in turn, fosters the longevity of social groups. The term social cohesion implies a form of attachment among group members that allows them to think and act as a group (Legare & Watson-Jones Reference Legare, Watson-Jones and Buss2015).

Group cohesion over time requires mechanisms for high fidelity transmission of group beliefs, values, and practices. We propose that the social stipulation and causal opacity of rituals make them ideally suited to high fidelity cultural transmission and inhibition of individual level innovation (Legare et al. Reference Legare, Wen, Herrmann and Whitehouse2015). Ritual behaviors lack a potentially knowable physical causal structure linking actions to outcomes (Humphrey & Laidlaw Reference Humphrey and Laidlaw1994). Causal opacity may be associated with a key facet of cultural learning that Norenzayan et al. identify: A “willingness to rely on faith in cultural traditions – over personal experience or intuition” (sect. 2.3, para. 1).

Where does the motivation to attend to group consensus, prestigious individuals, and individuals displaying CREDs come from in the context of ritual? We propose that selective social learning biases are motivated by affiliative goals that are adaptive in the context of group living (Herrmann et al. Reference Herrmann, Legare, Harris and Whitehouse2013; Legare et al. Reference Legare, Wen, Herrmann and Whitehouse2015; Watson-Jones et al. Reference Watson-Jones, Legare, Whitehouse and Clegg2014; Watson-Jones et al., Reference Watson-Jones, Whitehouse and Legarein press).

How did ritual cognition evolve? Rituals are cultural adaptations to the problems of group living that are built upon reliably developing features of our social group cognition. Through descent with modification, the motivation to affiliate with social groups and selective social learning biases may have become increasingly interconnected because of their downstream adaptive effects on social group behavior. Evolutionary feedback between learning mechanisms and the environment may have produced our species-specific ritual behavioral phenotype. The phenotypes that emerged from group living may have been selected for by an ongoing process of cumulative cultural evolution (Henrich Reference Henrich2009; Liénard & Boyer Reference Liénard and Boyer2006; Richerson & Boyd Reference Richerson and Boyd2005).

Ritual forms may differ between large- and small-scale societies. For example, there is evidence for two basic clusters of ritual dynamics, or “modes of religiosity” – a low-frequency, high-arousal cluster linked to the formation of small cohesive communities (imagistic mode) and high frequency, low-arousal cluster associated with larger, more centralized social morphology (doctrinal mode) (Atkinson & Whitehouse Reference Atkinson and Whitehouse2011). Big Gods are likely only associated with the doctrinal mode of religious transmission. Big Gods and CREDs increase in importance when it becomes impractical to monitor interactions on a large scale. As ritual coevolved with the expansion of social groups, concepts surrounding moralizing high gods could then act as reinforcers of social norms through their ability to punish individual transgressions that might damage the cohesion and cooperation of the community.

The problem of coordinated and cooperative group action is one of the greatest challenges of social group living (Tooby et al. Reference Tooby, Cosmides and Price2006). Rituals increase within group functioning by providing a means of identifying in-group members, displaying group commitment, facilitating cooperation with coalitions, and increasing social group cohesion. The social functions of ritual have allowed human groups to increase the scale of cooperation, facilitate collective action, and through incorporating concepts of supernatural punishment, promote prosociality. The selective social learning mechanisms associated with ritual cognition may have become increasingly specialized for affiliative functions within social groups. The social-stipulation and causal opacity of ritual also facilitate high fidelity cultural transmission over time.