British football fans completed this correlational survey. Willingness to lay down one’s life for a group of non-kin, well documented historically and ethnographically, represents an evolutionary puzzle. Building on research in social psychology, we develop a mathematical model showing how conditioning cooperation on previous shared experience can allow individually costly pro-group behavior to evolve. The model generates a series of predictions that we then test empirically in a range of special sample populations (including military veterans, college fraternity/sorority members, football fans, martial arts practitioners, and twins). Our empirical results show that sharing painful experiences produces “identity fusion” – a visceral sense of oneness – which in turn can motivate self-sacrifice, including willingness to fight and die for the group. Practically, our account of how shared dysphoric experiences produce identity fusion helps us better understand such pressing social issues as suicide terrorism, holy wars, sectarian violence, gang-related violence, and other forms of intergroup conflict. Some of the greatest atrocities have been caused by groups defending or advancing their political aspirations and sacred values. In order to comprehend and address the wanton violence of war, terrorism and genocide, it is necessary to understand the forces that bind and drive human groups. This five year programme of research investigates one of the most powerful mechanisms by which groups may be formed, inspired, and coordinated: ritual. Studying how children learn the rituals of their communities will shed light on the various ways in which rituals promote social cohesion within the group and distrust of groups with different ritual traditions. Qualitative field research and controlled psychological experiments will be conducted in a number of troubled regions (including Northern Ireland, the Middle East, Nepal, and Colombia) to explore the effects of ritual participation on ingroup cohesion and outgroup hostility in both general populations and armed groups. New databases will be constructed to explore the relationship between ritual, resource extraction patterns, and group structure and scale over the millennia. These interdisciplinary projects will be undertaken by international teams of anthropologists, psychologists, historians, archaeologists, and evolutionary theorists.

For this study, participants of all Premier League teams were given the opportunity to participate to prevent the research purpose being revealed. However, the study was predominantly advertised to the relevant teams’ fan groups (five consistent winners, and five perennial losers). An online questionnaire was advertised across social media (i.e. Facebook, Twitter), on online fan forum groups, dedicated fan blogs and across student networks. The online nature of the study allowed the research to reflect the cross-national diversity of the cohort, as teams from across the UK were included. A £100 prize was offered as an incentive to complete the study.