Across the historical and ethnographic records, from warriors and soldiers to suicide bombers and religious martyrs, humans have proven capable of not just cooperating within groups, but of making extremely costly personal sacrifices for them. Extreme self-sacrificial behaviour presents an evolutionary puzzle: how can a trait that calls for an individual to make the ultimate sacrifice, defending a group of people they are not related to, persist over evolutionary time? A new study, published in Nature’s Scientific Reports and led by the University of Oxford, provides insight into the causes of self-sacrifice in violent conflicts around the world, from holy wars to gangland violence.
The study used a combination of mathematical modelling and eight studies with groups ranging from army veterans to martial artists to find that sharing strong negative experiences can enable extreme cooperation among members for the sake of the group. Researchers theorise that human evolution explains the origin of this visceral bonding over shared painful experiences.
A growing body of experimental evidence suggest that willingness to fight and die for the group may be motivated by “identity fusion” – a normal (i.e., not psychopathological) form of group alignment in which the boundary between personal and social identity becomes porous, producing a visceral sense of oneness with the group.
The researchers were interested in what causes identity fusion and tested preliminary psychological evidence suggesting that one powerful cause of identity fusion is sharing painful and frightening experiences. An idea is that the the human brain, while “wired” for sacrificial behavior towards close kin, makes “mistakes” by facilitating pro-group behavior irrespective of genetic relatedness. The impetus for self-sacrifice by group members is often couched in the language of kinship; and empirical studies show that the effects of identity fusion on pro-national outcomes is partially mediated by feelings of family-like ties.
First author Professor Harvey Whitehouse, from the School of Anthropology, says: ‘The theory that sharing negative experiences produces powerful social bonds was initially inspired by my fieldwork among the tribes of Papua New Guinea, where warriors often went through extremely painful initiation rituals. Since then we’ve found these effects in a much wider range of groups, from Libyan insurgents to Americans affected by the Boston Marathon bombings. This new paper presents a mathematical model that might explain why shared suffering leads to such strong commitment to the group, alongside a very broad range of evidence from the real world.’
The paper looked at whether willingness to perform costly acts for the group is a behavioural strategy that evolved in human ancestors to enable success in high-risk collective activities and between-group conflicts. Groups whose members fused together after sharing painful experiences would be more likely to survive in between-group conflicts, whereas ancestral groups that did not fuse would be less likely to continue. In modern groups, the willingness to sacrifice for the group would be expressed only under extreme conditions, the paper suggests.
A co-author and psychologist, Dr Jonathan Jong says: ‘We deliberately cast a wide net to test how widespread this phenomenon is and found that across a very broad spectrum of events, the same effect crop up again and again, from experiences of natural disasters and armed conflict to painful martial arts rituals to loss by our favourite sports teams.’
Dr Christopher Kavanagh, cognitive anthropologist at the School of Anthropology, University of Oxford says: ‘Brazilian Jiu Jitsu and other martial arts for many people in the modern world provide some of their most intense and challenging physical experiences. It’s no surprise that we find the same kind of intense psychological bonding prevalent amongst these kinds of groups. Belt-whipping gauntlets might be unique to Brazilian Jiu Jitsu, but it is a common practice in martial arts to endure severe hardships in training collectively.’
Dr Michael Buhrmester, post-doctoral fellow at the Institute of Cognitive and Evolutionary Anthropology at the University of Oxford says: ‘What struck us most about this project was the consistency of the findings across such a diverse array of contexts. Most research reports on similar topics tend to examine one or two contexts. We examined more than six.’
And Martha Newson, DPhil student in Anthropology says: ‘We found that the worst performing clubs are likely to secure the most devoted fans. This may not be particularly surprising for ardent football fans but what’s exciting here is that this “post-disaster” bonding psychology occurs not only in fans, but in so many other contexts.’
Detail
The researchers used mathematical models to generate a series of hypotheses tested in experiments: shared experience promotes willingness to perform extreme pro-group action; shared negative experiences make individuals contribute more than euphoric experiences; the more intense the experience the stronger the pro-social effects; the effect of shared negative experiences on pro-social behaviour is much stronger where groups compete directly against other groups rather than if they cooperate against nature; and the effects of shared negative experience can be stronger than those of kinship.
The models aimed to capture the conditions faced by human ancestors tens of thousands of years ago. The researchers speculated that under threatening conditions, having a shared evolutionary future was a more decisive factor in cooperation and self-sacrifice than shared ancestry. Adaptation and survival was particularly difficult during the Late Pleistocene more than 100,000 years ago, when the environment was highly variable and when competition for limited resources was high, note the authors.
The research was by a team of international researchers from the University of Oxford; University of Tennessee, USA; the University of Melbourne, Australia; National University of Distance Education, Spain; Queen’s University, Belfast; the University of London and RAND Corporation.
