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Hadza Hunter-Gatherers and the Evolution of Human Cooperation: Evidence Against Partner Choice Models

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Hadza Hunter-Gatherers and the Evolution of Human Cooperation: Evidence Against Partner Choice Models University of Pennsylvania ScholarlyCommons Publicly Accessible Penn Dissertations 2019 Hadza Hunter-Gatherers And The Evolution Of Human Cooperation: Evidence Against Partner Choice Models Kristopher Michael Smith University of Pennsylvania, [email protected] Follow this and additional works at: https://repository.upenn.edu/edissertations Part of the Social Psychology Commons Recommended Citation Smith, Kristopher Michael, "Hadza Hunter-Gatherers And The Evolution Of Human Cooperation: Evidence Against Partner Choice Models" (2019). Publicly Accessible Penn Dissertations. 3535. https://repository.upenn.edu/edissertations/3535 This paper is posted at ScholarlyCommons. https://repository.upenn.edu/edissertations/3535 For more information, please contact [email protected]. Hadza Hunter-Gatherers And The Evolution Of Human Cooperation: Evidence Against Partner Choice Models Abstract Human cooperation is exceptional in the animal kingdom, and explaining its evolution is a puzzle. One hypothesis is that the ability to track others’ reputations and to choose our cooperative partners created biological markets, and competition within these markets selected for cooperators. Here, I test this hypothesis from the Hadza of Tanzania, one of the last remaining foraging populations. In Chapter 1, I use longitudinal data tracking cooperation in an economic game and residence patterns. In every year, contribution levels to the public good are similar within residence camps, fulfilling a necessary condition for the evolution of cooperation. However, cooperators in previous years were not more likely to live with cooperators in future years. Further, at the individual level, previous contributions did not predict future contributions. In Chapters 2 and 3, I use data from a ranking task in which Hadza ranked their campmates on character traits, hunting ability, and who they would like to live with in the future. In Chapter 2, I examine whether Hadza agree on perceptions of moral character. The Hadza disagree on which of their campmates exhibit moral character. The Hadza do agree though on what traits (e.g., generosity and hard work) contribute to overall moral character. These results indicate that the Hadza use similar criteria for evaluating moral character but do not agree on who exhibits these traits. The lack of agreement on perceptions of moral character may be due to the lack of stable moral dispositions among the Hadza. Finally, in Chapter 3, I examine which traits the Hadza prefer when choosing potential campmates. I find that the Hadza have only weak preferences to live with campmates that exhibit characters traits, and instead have stronger preferences to live with men who are better hunters. Further, there is no evidence that being a preferred campmate results in any benefits ot one’s reproductive success, further undermining partner choice theories. Together, these results indicate that partner choice and other reputation-based strategies do not maintain cooperation among the Hadza, and more broadly, suggests that such mechanisms were not responsible for the evolution of human cooperation. Degree Type Dissertation Degree Name Doctor of Philosophy (PhD) Graduate Group Psychology First Advisor Coren L. Apicella Keywords evolution of cooperation, Hadza, hunter-gatherers, moral character, partner choice, reputation Subject Categories Social Psychology This dissertation is available at ScholarlyCommons: https://repository.upenn.edu/edissertations/3535 ACKNOWLEDGMENT Appropriate to a dissertation on cooperation, I was only able to complete this with the help and support of mentors, friends, and family. I want to thank the department for its support and the opportunity. I would also like to thank my committee, Geoffrey Goodwin, Michael Platt, and Coren Apicella for their feedback and support on this dissertation. I am especially grateful to Coren Apicella for her mentorship, who has truly been a model advisor over the years. She gave me the freedom and opportunity to pursue a wide range of research interests, but also challenging and pushing me to learn more and think deeper. I’m a better scientist because of her. Coren was also supportive, kind, and encouraging, and always made time for me when I needed. Last year, during the lowest point of my PhD, Coren looked out for me when no else I did and fought on my behalf, even though I was not officially her student at the time. I’m really only here now because of her. In fact, this last year working with Coren has been the best year of graduate school for me. Thank you, Coren; I could not imagine a better mentor than you. I am also thankful for the friends and lab mates in graduate school and the support they provided; from discussing ideas, helping me with new skills, giving feedback, to encouraging me and being there as friends. Thank you, Fatima Aboul-Seoud, Corey Cusimano, Molly Elson, Daniel Medina, Eugene Olkov, Keana Richards, Claire Ryder, Victoria Tobolsky, Megan Williams, and Joyce Zhao. I only had the opportunity to pursue a PhD because of a number of people who believed in me and encouraged my love of science. They not only gave me my first experiences in research, but also advised me each step along my academic career. Thank ii you, Daniel Hruschka, Julie Bauer Morrison, Steven Neuberg, Oliver Sng, and Karina Sokol-Tinsley; I am fortunate that they all remain mentors and role-models in my life. I would also like to thank my family and my partner, Vivienne Varay, for their support over the years. Though far in distance, my family was always close in supporting and cheering me on. And Vivienne especially was patient and encouraging as I pursued my PhD, and she helped me through all of the setbacks I experienced. I am grateful for their love and support. Much of the data in this dissertation were collected from a field season in the Fall of 2016. This work was generously supported by the Templeton Religion Trust with a subgrant through the Moral Beacons Project and Wake Forest University. I thank Audax Mabulla for administrative support in Tanzania. I also thank Endeko Endeko, Deus Haraja, and Ibrahim Mabulla for their help in data collection and for keeping me alive in the field (which, to be honest, I did not make it an easy task for them). Finally, I want to thank Hadza for participating in the research and allowing me stay among them. It was a unique experience to spend that time with them, and I am grateful for all the lessons they taught me. I started graduate school with a number of preconceptions about human behavior, and no academic, article, or argument pushed me to abandon those assumptions as much as working with the Hadza did. Thank you for teaching me to appreciate the variation and diversity in human nature. iii ABSTRACT HADZA HUNTER-GATHERERS AND THE EVOLUTION OF HUMAN COOPERATION: EVIDENCE AGAINST PARTNER CHOICE MODELS Kristopher M. Smith Coren L. Apicella Human cooperation is exceptional in the animal kingdom, and explaining its evolution is a puzzle. One hypothesis is that the ability to track others’ reputations and to choose our cooperative partners created biological markets, and competition within these markets selected for cooperators. Here, I test this hypothesis from the Hadza of Tanzania, one of the last remaining foraging populations. In Chapter 1, I use longitudinal data tracking cooperation in an economic game and residence patterns. In every year, contribution levels to the public good are similar within residence camps, fulfilling a necessary condition for the evolution of cooperation. However, cooperators in previous years were not more likely to live with cooperators in future years. Further, at the individual level, previous contributions did not predict future contributions. In Chapters 2 and 3, I use data from a ranking task in which Hadza ranked their campmates on character traits, hunting ability, and who they would like to live with in the future. In Chapter 2, I examine whether Hadza agree on perceptions of moral character. The Hadza disagree on which of their campmates exhibit moral character. The Hadza do agree though on what traits (e.g., generosity and hard work) contribute to overall moral character. These results indicate that the Hadza use similar criteria for evaluating moral character but do not agree on who exhibits these traits. The lack of agreement on perceptions of moral character may be due to the lack of stable moral dispositions among the Hadza. Finally, in Chapter 3, I examine iv which traits the Hadza prefer when choosing potential campmates. I find that the Hadza have only weak preferences to live with campmates that exhibit characters traits, and instead have stronger preferences to live with men who are better hunters. Further, there is no evidence that being a preferred campmate results in any benefits to one’s reproductive success, further undermining partner choice theories. Together, these results indicate that partner choice and other reputation-based strategies do not maintain cooperation among the Hadza, and more broadly, suggests that such mechanisms were not responsible for the evolution of human cooperation. v TABLE OF CONTENTS ACKNOWLEDGMENT .......................................................................................................... II ABSTRACT ................................................................................................................................ IV LIST OF TABLES ................................................................................................................
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