Chimpanzee personality and its relations with cognition and health: a comparative perspective

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). 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.