Collective decision-making in the face of intergroup conflict: theory and tests

Abstract

Recently many studies have been published that describe and explain how groups of social animals make collective decisions and coordinate their actions. However, these studies mostly focus on isolated groups, and do not consider how these groups might behave under different social contexts, such as when there is the threat of fighting with rival groups. In this thesis, I present two complementary theoretical models that explore how simple differences in leadership and decision-making dynamics within groups can have large impacts on the investment and initiation of intergroup conflict. In Chapter One, I present an agent-based model of intergroup conflict to investigate how the presence of leaders and followers influences the dynamics of conflict initiation and conflict investment. I find that changing different parameters such as maximum group size, migration rate and intergroup encounter rate cause either between or within group competition to be emphasised which changes the levels of conflict investment. When between group competition is low, follower investment in conflict is low and leaders are forced to overcompensate and contribute (“heroic leadership”). However, when between-group competition is high, follower investment in conflict is high and leaders can free-ride and do not contribute (“exploitative leadership”). We find that when followers contribute then leaders are incentivised to behave more aggressively and initiate more intergroup conflict. In Chapter Two, I present a theoretical model to investigate how differences in shared decision-making can influence conflict escalation in groups consisting of leaders and followers. I find that when the sharing rules of conflict are biased towards leaders gaining more benefits or paying less costs than followers then leaders evolve a higher optimum for pursuing aggressive, conflict escalating strategies. When this is true, increased shared decision-making by allowing for increased follower control of collective decision-making results in the evolution of more peaceful intergroup interactions. In the reverse case, when sharing rules favour followers, then increasing their share of decision-making increases the aggressive conflict-escalating tendencies of the group. This theoretical model shows how different decision-making and political structures can be important for favouring the evolution of war or peace, and demonstrates how democratic peace theory might apply to non-human animal societies without complex institutions