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The evolutionary processes that shape individual variation in continuous behavioural traits remain poorly understood. While the emerging discipline of animal personality is providing increasing evidence that consistent individual differences in behaviour have significant fitness consequences, cognitive traits are yet to be explored in the same manner. My general objective in this thesis was twofold. First, I aimed to examine the ecological significance and fitness consequences of the cognitive trait innovative problem solving-performance, using a population of great tits (Parus major). Second, I aimed to explore the mechanisms underlying the functional significance of ‘exploration behaviour’ a captive measure of the reactive- proactive personality axis, focusing specifically on foraging and risk-taking behaviour. This two-trait approach was expected to shed light on whether personality and cognition simultaneously influence fundamental behaviours. By carrying out behavioural assays on birds temporarily held in captivity, I showed that success at solving a food-motivated problem was repeatable within individuals, consistent between two different tasks and independent of exploration behaviour. Problem-solving performance was positively related to clutch size and fledgling number, established when birds were released back into the wild. Furthermore, when rearing offspring, solvers had shorter working day lengths than non-solvers and foraged over smaller ranges without compromising either provisioning quantity or quality. However, solver females were also more likely to desert their broods than non-solvers and consequently there was little evidence to suggest that directional selection acted on problem-solving performance. In comparison to non-solvers, solver males were also found to be poorer at competing for limited food resources during the winter. Together these findings suggest that costs and benefits are associated with problem-solving performance, which together may act to maintain variation in this trait. My thesis also provides some of the first evidence that exploration behaviour is related to both foraging and risk-taking behaviour in the wild. In comparison to relatively slow explorers, fast exploring males were better competitors at feeders during the winter. Relatively fast and slow explorers also differed in a number of foraging behaviours during offspring provisioning, although not always in the direction predicted from captive work on other populations. Finally, while exploration behaviour was positively correlated with risk- taking behaviour amongst breeding females during incubation, it did not predict nest desertion in response to the risk associated with being trapped by field workers. Collectively these findings suggest that personality measured in captivity has specific but not general power to predict behaviour in the wild. An important facet of evolution is that natural selection is rarely likely to act on a single trait in isolation owing to correlations between traits. This thesis demonstrates how important behaviours in the wild can be simultaneously linked to multiple sources of consistent behavioural variation. It also represents the first large-scale investigation of how variation in a cognitive trait relates to natural behaviour, reproductive life-history variation and fitness in wild animals. Using this individual-based approach in a natural setting may prove to be a useful tool for understanding how selection acts on cognitive traits.

I develop social evolution theory to study the evolution of cooperation as follows: (1) Many organisms undergo a dispersal phase prior to breeding; I demonstrate that knowing ones dispersal status aids the evolution of helping (by non-dispersers) and harming (by dispersers). (2) Policing driven by group-benefits may be selected to enforce cooperation in human and animal societies. I extend existing theory to show that policing may be harder to evolve that previously thought, but that it is maintained more readily than it evolves. (3) Archeological and anthropological evidence suggests that warfare was prevalent during our evolution. I show that, contrary to previous suggestions, between-group competition can favour any social behaviour (pro-social or anti-social) so long as it helps the group compete, and that such traits can be altruistic or mutually beneficial. (4) Reproductive leveling is analogous to policing; in the human literature there is doubt as to whether it can evolve. I extend my previous work to consider the coevolution of culturally and genetically inherited traits for reproductive leveling and selfishness. I find that cooperation can evolve between non-kin if they share the same culture. (5) Monogamy is thought to favour the evolution of cooperative breeding. I show that in the simplest case, because of the cost of competition between non-dispersing siblings, the level of promiscuity has little or no effect on the evolution of cooperation. (6) Spatial structure (limited dispersal) is thought to favour the evolution of inter-specific mutualisms as it aligns the partners’ interests. I consider the case of plant-fungi mutualisms and show that spatial structure can disfavour cooperation if it limits the potential fungal partners available to the plant.