Relationship Formation and Maintenance in Captive Chimpanzees (Pantroglodytes) Open Access

Calcutt, Sarah (2016)

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Social risk is a unique domain of risk whereby the costs, benefits and uncertainty of an interaction stem from the ability to predict the behavior of another individual. The unique characteristics of social risk cause humans to overvalue the costs of a socially risky decision when compared to that of economic risk. While many studies investigate the cognitive requirements of social decision-making in non-human primates, the purpose of this study was to examine whether uncertainty in the social realm influences relationship formation and maintenance in chimpanzees. We accomplished this through the use of both an economic trust-game and an observational study. The eight subjects in the trust-game preferred to take economic risks to social risks and based their choices on the actions of their partners as opposed to their relationships with them. Similarly, when we observed the social behaviors of chimpanzees in two newly formed groups we found that they did not rely on only one strategy but both maintained old relationships and invested in new ones. These studies demonstrate that, like humans, chimpanzees are averse to social betrayal and base their social decisions on the costs and benefits of an interaction as opposed to solely on their familiarity with a group mate.

Table of Contents


1.1 The Domain of Social Risk 6

1.2 Factors that Influence Socially Risky Decisions 9

1.2.1 Emotions 9

1.2.2 Relationship 14

1.2.3 Disposition 17

1.3 Objective 19

1.4 References 21


2.1 Methods 36

2.1.1 Subjects and housing 36

2.1.2 Experiment I: Chimpanzee trust game 37 Social condition 37 Non-social condition 38 Test sessions 42 Behavioral observations 44 Training and criteria 45

2.1.3 Experiment II: Dyadic variation trust game 46

2.1.4 Control conditions 47

2.2 Predictions, Analyses and Results 50

2.2.1 Question 1: Are chimpanzees more averse to a loss resulting from the choices of a conspecific than a loss incurred through non-social means? 50 Analysis 51 Results 51

2.2.2 Question 2: Do individual differences in social risk preferences correlate with independent measures of social behavior? 55 Analyses 56 Results 56

2.2.3 Question 3. Does quality of social relationship outside of the experimental setting influence decisions made during a social investment game? 57 Analyses 57 Results 58

2.2.4 Control Conditions 61 Analyses 62 Results 63 Closed-door/ no partner 63 Open-door/ no partner 63

2.3 Discussion 65

2.4 References 72


3.1 The Present Study 82

3.2 Subjects and Housing 84

3.3 Question 1: Is there a correlation between the formation of a dominance hierarchy over time and social behaviors in two newly formed groups of chimpanzees? 87

3.3.1 Methods 88

3.3.2 Analyses 90

3.3.3 Results 92

3.4 Question 2: Do chimpanzees in a newly formed group direct more affiliation, aggression and support towards familiar or unfamiliar group members? 95

3.4.1 Analyses 96

3.4.2 Results 99 Social behaviors 99 Support 103 Top Grooming Partners 104 Reciprocity 106 Social Network Graphs 106

3.5 Question 3: How do individual characteristics such as rank or number of familiar group members influence how an individual responds to other familiar or unfamiliar individuals? 109

3.5.1 Analyses 110

3.5.2 Results 110

3.6 Discussion 111

3.7 References 119


4.1 Irrational Biases and Trust 130

4.2 Relationship Formation and Maintenance 134

4.3 Future Studies 137

4.4 Conclusion 139

4.5 References 143


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