Throughout the history, what has been causing tremendous suffering is groups of people fighting each other. While behavioral science research has advanced our understanding of such intergroup conflict, it has largely focused on micro-level processes within and between groups. Disciplines that employ a more historical perspective like climate studies or political geography report that macro-level pressures due to changes in climate and economic scarcity can go along with social unrest and wars. In our project we addressed two main topics, using archival analyses, field observations, and laboratory experiments:
1. How do the macro-level pressures relate to micro-level group dynamics?
Peaceful co-existence and trade among human groups can be fragile and intergroup relations frequently transition to violent exchange and conflict. Here we specify how exogenous changes in groups’ environment and ensuing carrying-capacity stress can increase individual participation in intergroup conflict, and out-group aggression in particular. In intergroup contest experiments, individuals could contribute private resources to out-group aggression (versus in-group defense). Environmental unpredictability created psychological stress and increased participation in and coordination of out-group attacks. Archival analyses of interstate conflicts showed, likewise, that sovereign states engage in revisionist warfare more when their pre-conflict economic and climatic environment was more unpredictable. Given that participation in conflict is wasteful, environmental unpredictability not only made groups more often victorious but also less wealthy. Macro-level changes in the natural and economic environment can be a root cause of out-group aggression and turn benign intergroup relations violent.
2. What are the neurohormonal and brain mechanisms explaining the link between outside pressures, like carrying-capacity stress, and inclinations to violently aggress outgroups?
To understand when and why intergroup relations change from peaceful to violent, we developed a theoretical framework mapping out the different interdependence structures between groups. According to this framework, cooperation can lead to group expansion and ultimately to carrying-capacity stress. In such cases of endogenously created carrying-capacity stress, intergroup relations are more likely to become negatively interdependent and parochial competition can emerge as a response. Using a range of neuroscience methods we examined the cognitive, neural, and hormonal building blocks of parochial cooperation, and specified the roles of the neurohormones oxytocin and testosterone, and neural activity in the temporoparietal junction and dorsolateral prefrontal cortex as key to parochialism.
