Street fights increase social tension and social affiliation in human bystanders

Naturalistic observations of conflict events documented that, similarly to nonhuman primates, human bystanders take an active role in managing the negative consequences of the conflicts.However, although in nonhuman primates it has been suggested that conflicts increase social tension in bystanders by in turn affecting their social propensity, in humans there is still lack of evidence. By applying observational methods from primatology, we conducted video analysis of streets fights recorded by surveillance cameras in public spaces of Amsterdam in order to evaluate whether conflicts generate social tension among human bystanders and promote bystanders’ affiliation as a tension-reduction mechanism. We found that witnessing a street fight increased the expression of anxiety-related behaviours in bystanders and their propensity to engage in non-physical and physical affiliative interactions. The occurrence of affiliation improves in turn the emotional state of bystanders by reducing their expression of anxiety-related behaviours. Our work offers for the first time a behavioural-based analysis of the emotional drivers underpinning bystanders’ activity in real-life conflicts.