Behavioural Flexibility, Fertility and Social Network Influences in Human and Non-Human Primates

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My aim is to understand how evolutionary processes influence the behaviour of human and non-human primates. More specifically, I am interested in exploring those aspects that we share with other primate species, and those that make us different. One shared feature is argued to be our high level of behavioural flexibilitythe ability to cope with changes in the ecological and social environment. At the same time, however, humans and other primates have been shown to possess stable personalities; that is, our behaviour is often very consistent across time and circumstance. Displaying the same behaviour over different contexts is the very opposite of flexibility, and raises questions of why stable personality traits should exist. *** Here, I propose to investigate the link between personality and plasticity among South African vervet monkeys. It has been argued that consistent differences in growth rate between individuals leads to stable personality traits (e.g., animals that are growing fast may need to be more aggressive, more active and take more risks to ensure they meet their energy demands via foraging), and that such differences may be reinforced over the course of development. Longitudinal studies, combining observational and experimental data, from infancy to adulthood, can help answer this question. It has also been suggested that personality and plasticity are complementary: animals may show average differences in their behaviour, and they may also vary in the strength of their response to environmental change. Using experimental and observational data on vervet monkeys, I will test whether personality predicts plasticity within and between individuals, and if this varies across different life stages and between the sexes. These data will provide valuable information on the scope and limits of vervet plasticity, and their likely ability to cope with rapid climate change. *** The second part of my proposal deals with human behaviour, and focuses on our differences from other primates. Here, the emphasis is on how cultural shifts in modern, industrial economies influence reproductive decisions, leading to much smaller family sizes than evolutionary theory predicts. One suggestion is that economic development leads to changes in our social networks (weaker links, with fewer kin), which in turn affects the decision to reproduce. Here, my trainees, collaborators and I will compare social networks in Canada, where fertility is below replacement levels (1.61 children per woman), with a less developed nation, Samoa, where fertility remains high (5.10 children per woman). Understanding why fertility varies, and what influences people's reproductive decisions will help contribute to more accurate population forecasts, and potentially explain why people sometimes fail to reach their family size goals in industrial nations.