A comparative analysis of play behaviour in primates and carnivores
This thesis considers the evolution of play behaviour, focusing on comparative analyses of extant primates and carnivores from various perspectives, including intra-specific analyses, life-history, socio-ecology, and brain anatomy, taking data from the existing literature, and using phylogenetic comparative techniques. Phylogenetic reconstructions suggest that each play category represents its own evolutionary trajectory, and support previous findings that social play, being the most ancient form of play in primates, may represent a distinct category of behaviour. Analyses of intra-specific play patterns proved difficult due to a lack of available data in the literature, but point to the importance of controlling for variables that differ between populations of the same species, such as group composition, and research effort. Comparative analyses of life-history variables and play demonstrate that precocial species play more than altricial species. Precocial species have a relatively shorter developmental period of postnatal brain development, and may therefore require the neurological and physiological benefits afforded by play behaviour in order to hone brain development prior to adulthood. Comparative analyses of socio-ecology and play suggest that larger groups require increased play time budgets, possibly because of a need to fulfil the social skills required to maintain group cohesion. Social networks of the population (clique size and network size) predict social play frequency in primates. Contrary to previous findings, I found no evidence that diet is a good indicator of time spent in play, although basal metabolic rate does correlate with play, suggesting that other socio-ecological factors contribute to the performance of play. Comparative analyses of brain components and play indicate that brain correlates are selective and do not apply to all regions. There are strong correlations between socio-cognitive, motor, emotional, and also visual areas of the brain and social play in primates, namely the neocortex, cerebellum, visual cortex and LGN, vestibular complex, striatum, medulla, amygdala, and hypothalamus. Although play is a difficult ethological topic, it appears to be vital to development and life in social groups.