Collective rituals are present in all known societies, but their function is a matter of long-standing debates. Field observations suggest that they may enhance social cohesion and that their effects are not limited to those actively performing but affect the audience as well. Here we show physiological effects of synchronized arousal in a Spanish fire-walking ritual, between active participants and related spectators, but not participants and other members of the audience. We assessed arousal by heart rate dynamics and applied nonlinear mathematical analysis to heart rate data obtained from 38 participants. We compared synchronized arousal between fire-walkers and spectators. For this comparison, we used recurrence quantification analysis on individual data and cross-recurrence quantification analysis on pairs of participants' data. These methods identified fine-grained commonalities of arousal during the 30-min ritual between firewalkers and related spectators but not unrelated spectators. This indicates that the mediating mechanism may be informational, because participants and related observers had very different bodily behavior. This study demonstrates that a collective ritual may evoke synchronized arousal over time between active participants and bystanders. It links field observations to a physiological basis and offers a unique approach for the quantification of social effects on human physiology during real-world interactions.social interaction | mirroring | recurrence plots | collective effervescence | social anthropology

Moralistic gods, supernatural punishment and the expansion of human sociality Benjamin Grant Purzycki 1 , Coren Apicella 2 , Quentin D. Atkinson 3,4 , Emma Cohen 5,6 , Rita Anne Mcnamara 7 , Aiyana K. Willard 8 , Dimitris Xygalatas 9,10,11 , Ara norenzayan 7 & Joseph henrich 7,12,13 Since the origins of agriculture, the scale of human cooperation and societal complexity has dramatically expanded 1,2 . This fact challenges standard evolutionary explanations of prosociality because well-studied mechanisms of cooperation based on genetic relatedness, reciprocity and partner choice falter as people increasingly engage in fleeting transactions with genetically unrelated strangers in large anonymous groups. To explain this rapid expansion of prosociality, researchers have proposed several mechanisms 3,4 . Here we focus on one key hypothesis: cognitive representations of gods as increasingly knowledgeable and punitive, and who sanction violators of interpersonal social norms, foster and sustain the expansion of cooperation, trust and fairness towards co-religionist strangers 5-8 . We tested this hypothesis using extensive ethnographic interviews and two behavioural games designed to measure impartial rule-following among people (n = 591, observations = 35,400) from eight diverse communities from around the world: (1) inland Tanna, Vanuatu; (2) coastal Tanna, Vanuatu; (3) Yasawa, Fiji; (4) Lovu, Fiji; (5) Pesqueiro, Brazil; (6) Pointe aux Piments, Mauritius; (7) the Tyva Republic (Siberia), Russia; and (8) Hadzaland, Tanzania. Participants reported adherence to a wide array of world religious traditions including Christianity, Hinduism and Buddhism, as well as notably diverse local traditions, including animism and ancestor worship. Holding a range of relevant variables constant, the higher participants rated their moralistic gods as punitive and knowledgeable about human thoughts and actions, the more coins they allocated to geographically distant co-religionist strangers relative to both themselves and local co-religionists. Our results support the hypothesis that beliefs in moralistic, punitive and knowing gods increase impartial behaviour towards distant co-religionists, and therefore can contribute to the expansion of prosociality.Among the other factors 2-4,7 that influence the emergence of human ultrasociality and complex societies, the diffusion of explicit beliefs in increasingly moralistic, punitive and knowledgeable gods may have played a crucial role 6,7 . People may trust in, cooperate with and interact fairly within wider social circles, partly because they believe that knowing gods will punish them if they do not. Additionally, through increased frequency and consistency in belief and behaviour sets, commitments to the same gods coordinate people's expectations about social interactions [5][6][7][8][9] . Moreover, the social radius within which people are willing to engage in behaviours that benefit others at a cost to themselves may enlarge as gods' powers to monitor and punish increase 10 . To account f...

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