The Dual Impact of Stress on Group Dynamics and Intergroup Conflict

In a groundbreaking study, researchers at Heinrich Heine University Düsseldorf (HHU) have uncovered the complex ways in which stress influences group dynamics and intergroup conflict. The findings, published in the *Proceedings of the National Academy of Sciences* on July 15, 2025, reveal that physiological stress messengers can simultaneously bolster cooperation within groups while fostering aggression toward out-group members.

The research led by Professor Dr. Tobias Kalenscher from HHU's Comparative Psychology research team examined the effects of two neurochemicals, noradrenaline and cortisol, on social behavior during intergroup conflicts. According to the study, cortisol promotes cooperative behavior among individuals within their own group, whereas noradrenaline tends to increase hostility toward out-groups.

The persistent nature of violent conflicts between groups, even amidst mutual suffering, raises critical questions about social behavior in high-stress situations. Professor Kalenscher emphasized, "Stress does not universally incite aggression or cooperation; rather, the resulting behavior depends on which neurochemical pathway is activated during stress and the perceived identity of the counterpart—friend or foe."

The research involved participants who were administered either hydrocortisone, mimicking cortisol's activity, or Yohimbin, which enhances noradrenaline effects. Participants engaged in economic games where they could choose to benefit their in-group at a cost to out-group members. The study's lead authors, Damon Dashti and Luca Marie Lüpken, noted, "Our findings suggest that stress not only drives individuals to cooperate with familiar group members but also encourages antagonism towards outsiders, thus elucidating the neurobiological mechanisms behind increasing societal polarization."

The implications of this study extend beyond academic interest, offering insights into current global conflicts and polarization trends. As societies face rising tensions, understanding the neurobiological underpinnings of stress responses could inform strategies to mitigate conflict and foster cooperation.

The results also prompt a re-evaluation of stress management in social contexts, particularly in environments characterized by high levels of intergroup competition. This research highlights the necessity of addressing both psychological and physiological factors in conflict resolution strategies.

The HHU study provides a vital lens through which to view the dynamics of group behavior under stress, reinforcing the idea that stress responses are not merely individual experiences but have significant social ramifications. As Professor Kalenscher concluded, "Understanding these mechanisms is crucial for developing interventions that could reduce intergroup hostility and enhance collaborative efforts across diverse societal groups."

This research is a vital step toward comprehending the intricate relationship between stress, social behavior, and the escalating conflicts that define our times. The potential for these findings to influence future research and practical applications in conflict resolution and social cohesion is immense, paving the way for a deeper exploration into how we can better navigate the challenges posed by intergroup dynamics in an increasingly polarized world.