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Chimpanzee personality and its relations with cognition and health: a comparative perspective Drew Altschul Thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy in Psychology to The University of Edinburgh July 2017 Declaration I hereby declare that this thesis is of my own composition, and that it contains no material previously submitted for the award of any other degree. The work reported in this thesis has been executed by myself, except where due acknowledgement is made in the text. Signed, Drew Altschul i Acknowledgements This research was funded in part by The University of Edinburgh’s Principal Career Development Scholarships, the Great Britain Sasakawa Foundation, and the Department of Psychology and many research support grants. There are many people to whom I owe thanks, for the completion of this thesis would not have been possible without them. Alexander Weiss and Ian Deary, my supervisors. Herbert Terrace and Greg Jensen, my collaborators on all things serial cognitive. Masaki Tomonaga, Testuro Matsuzawa, and other members of the Primate Research Institute, as well as Ruth Sonnweber, and Emma Wallace sponsors, all my collaborators in my work on chimpanzee cognitive testing. Steve Ross, Bill Hopkins, Jim King, Miho Inoue-Murayama, and David Sinn, my collaborators on the projects linking chimpanzee personality, stress, and longevity. My appreciation also goes out to the staff of the Edinburgh Zoo, as well as the chimpanzees and monkeys who took part in data collection, but I would like to reserve special thanks for the staff at Budongo Trail. I would like to acknowledge all of my many office mates, office neighbours, differentialists, journal club attendees, and other members of the department, current and former. In particular, I must thank Vanessa Wilson, Milan Valášek, Sebastian Sandoval Similä, Stuart Richie, Iva Čukić, Felix Suessenbach, Guillermo Puebla, Tom Booth, Aja Murray, Zander Crook, Calen Walsh, Lauren Robinson, Marieke Gartner, Conor Smith, and Samuel Gibbon. I also thank the Cambervillians, San Franciscans, New Yorkers, and Oregonians for their unique contributions of support. ii Finally, I would like to thank my family, my parents, brothers, and sister. My most gracious thanks go to Ella, for always being there, putting up with my displays, and encouraging me when I needed it the most. iii A Note on Personal Pronouns This thesis is based to a large extent on published work and work under review. In order to maintain consistency with the published literature, and to acknowledge the collaborative nature of the work, “we” rather than “I” is used throughout. iv Abstract This thesis aimed to address two main questions. First, considering that personality is frequently associated with cognitive abilities in humans, do chimpanzees’ personalities and cognitive capacities covary in ways similar to what is observed in humans, as well as older evolutionary cousins, rhesus macaques? Second, given that human and animal personality have previously been shown to relate to health and longevity, does personality in chimpanzees also relate to various measures of health? Chapter 1 provides an introduction to and brief history of comparative personality psychology, particularly in the context of intelligence research and psychosomatic medicine. Chapter 2 describes three studies with a group of 19 zoo-housed chimpanzees who interacted with touchscreen tasks over the course of 3 years of research. We found that high Conscientious chimpanzees were more likely to stick with the tasks, and performed better as a results, but once their extra experience was taken into account, their performance advantage disappeared. However, we also found associations between better interest and performance with high Openness, high Extraversion, and low Agreeableness. In Chapter 3 we examine performance in conjunction with personality, with 9 rhesus macaques. The macaques also engaged with touchscreen tasks, but were expert subjects and displayed plateau performance. We found consistent associations between many measures of performance and both high Openness and high Friendliness (which is similar to Extraversion). v With Chapter 4 we transition to our studies of personality and health. Chapter 4 examines personality and longevity in a sample of 538 personality rated, captive chimpanzees. These chimpanzees were followed for between 6 and 23 years after being rated. We found that high Agreeableness chimpanzees were more likely to live longer, but no other personality traits had a significant impact on longevity. In Chapter 5, we compared biomarkers from samples of 177 chimpanzees housed at the Yerkes National Primate Research Centre, and 29,314 humans from the National Health and Nutrition Examination Survey. Both samples had been tested for the most common haematological and metabolic blood biomarkers, and we used these to assess stress in the form of allostatic load, between species. We found a similar structure of biomarkers in across humans and chimpanzees. In Chapter 6, we took our allostatic load measure from chapter 5 and looked at how it was associated with personality, in the same chimpanzee sample from the Yerkes Primate Centre, and in the longitudinal Midlife in the United States and Midlife in Japan biomarker study samples, which consisted of 993 and 382 individuals, respectively. We found that Agreeableness was associated with allostatic load in both human samples, whereas Dominance was associated with allostatic load in chimpanzees. Finally, Chapter 7 summarises the results presented in these five empirical chapters, and places our findings in the context of the existing literature. We discuss the limitations of the research, and offer some suggestions for future study. vi Lay Summary This thesis made two particular inquiries into the field of comparative personality psychology. First, are the dimensions of primate personality and cognitive ability associated with one another? If so, how? Considering the extensive positive evidence that has been reported in the human literature, we predicted that we would find similar associations in chimpanzees, and also macaques, though to a lesser extent. We studied both chimpanzee and rhesus macaque groups, collecting data on personality, cognitive performance, and participation in tasks, ultimately finding similarities in the relationships between personality, participation, and performance across species. Second, given that human and animal personality have previously been shown to relate to health and longevity, we investigated whether personality in chimpanzees is related to both mortality and stress, the latter of which we assessed using the results of several different blood tests. We found little consistency between the personality dimensions predicting higher stress and earlier mortality, but robust associations between several different personality dimensions and individual life outcomes. In these associations, we found some consistency with what has been reported for humans, as well as some effects that are distinctly chimpanzee. Overall, this thesis demonstrates the utility of personality to these types of experiments and analyses, particularly in large, well- powered studies. vii Contents Declaration ........................................................................................................................ i Acknowledgements .......................................................................................................... ii A Note on Personal Pronouns ....................................................................................... iv Abstract ............................................................................................................................ v Lay Summary............................................................................................................... vii 1 Individual differences in comparison .................................................................... 1 1.1 The development of a differential psychology of primates .............................. 1 1.1.1 Intelligence .................................................................................................... 2 1.1.1.1 The primate perspective ........................................................................ 4 1.1.1.2 Social cognition and chimpanzees ........................................................ 5 1.1.1.3 Physical cognition of chimpanzees ....................................................... 7 1.1.1.4 Can chimpanzee intelligence be explained by a general domain? ........ 8 1.1.2 Personality ..................................................................................................