From Conflict to Cohesion: The effect of intergroup competition on affiliation, oxytocin, and group cohesion in wild capuchin monkeys. Restricted; Files Only
Kovalaskas, Sarah (Summer 2025)
Abstract
Humans are notable for their high levels of cooperation and social tolerance—yet we are also selective about who we cooperate with and are capable of extreme intergroup violence. Evolutionary scientists have proposed that intergroup conflict has played a central role in shaping human psychology and the evolution of cooperation. This dissertation explores whether white-faced capuchins (Cebus imitator)—a highly social and tolerant Platyrrhine monkey that cooperates extensively with non-kin—may have followed a similar evolutionary pathway. Capuchins offer an ideal model for such questions due to their convergence in social and life history traits with humans and chimpanzees, group-level coordination, and frequent hostile intergroup encounters (IGEs). Over 11 months of fieldwork at the Capuchins de Taboga Research Project in Guanacaste, Costa Rica, I combined detailed behavioral observations with non-invasive hormone sampling to examine how IGEs shape within-group social behavior and urinary oxytocin (uOT) levels. IGEs were frequent and often intense, with over half involving aggression. The number of participants strongly predicted encounter intensity, and IGE frequency did not vary seasonally. Contrary to expectations, capuchins did not show broad increases in affiliation following IGEs. However, individuals who participated in encounters exhibited more cohesive social networks afterwards. Following high-intensity IGEs—typically involving greater group participation—we also observed a marked reduction in within-group aggression. In the course of this work, I also developed and validated a method for measuring Proline-8 (P8) uOT in this population. While social behaviors did not predict uOT levels as expected, males showed significantly higher baseline uOT than females, and levels in both sexes increased with rising temperatures. Together, these findings offer new methodological tools and theoretical insights into the role of conflict, cooperation, and the neuroendocrine mechanisms shaping social behavior in Platyrrhine primates.
Table of Contents
Table of Contents
Chapter 1: Introduction
1. Chapter 1: Introduction
1.1 The Evolutionary Roots of Parochial Altruism
1.2 Intergroup Conflict in Nonhuman Primates
1.3 Proximate Mechanisms of Parochial Altruism
1.4 Capuchins: Bullies of the Forest or Master Collaborators?
1.5 Specific Aims
Chapter 2: Between-Group Conflict
2. Intergroup encounters in wild white-faced capuchins (Cebus imitator) at a densely populated field site: Patterns of Occurrence, Intensity, and Participation
2.1 Introduction
2.2 Methods
2.3 Results
2.4 Discussion
Chapter 3: Endocrine Mechanisms
3. Measuring oxytocin in Wild Capuchins (Cebus imitator): Validation of urinary measures and social insights
3.1 Introduction
3.2 Methods
3.3 Results
3.4 Discussion
Chapter 4: Behavioral Consequences
4. Does fighting foster friendship?: How between-group conflict shapes social cohesion and affiliation in white-faced capuchins
4.1 Introduction
4.2 Methods
4.3 Results
4.4 Discussion
Chapter 5: Conclusions
5. Chapter 5: Conclusions
5.1 Summary of results
5.2 So, what about parochial altruism?
5.3 Future directions
References
About this Dissertation
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File download under embargo until 21 August 2027 | 2025-07-02 11:27:54 -0400 | File download under embargo until 21 August 2027 |
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