The Evolution of Co-operâtion
A fundamental question about all forms of collective animal behavior is how they evolved through natural selection. At various points in this book I have turned to arguments based on individuals adopting or evolving behaviors that increase their own fitness to explain or make predictions about group behavior. For example, group size distribution was described in terms of individuals attempting to join a group of a size that maximizes their fitness (chapter 2); foraging birds were described as balancing searching for food themselves with copying others (chapter 3); consensus decision-making and synchronization were described in terms of individuals co-ordinating so they can benefit from acting together (chapters 4 and 7). While such functional arguments are not the only way to understand the behavior of groups (and indeed have played a secondary role to mechanistic explanations in the other chapters of this book), they are an essential part of biology. This chapter gives an overview of how functional reasoning can be applied to collective animal behavior.
The theory of natural selection is grounded in the idea that those individuals exhibiting a behavior that provides them with higher than average fitness pass their genes, and thus their particular behavior, on to future generations. It is this idea that provides the basic assumption of evolutionary game theory models: those individuals adopting a strategy that provides them with higher than average fitness will increase in the population, while those with lower than average fitness will decrease. Despite the simplicity of this underlying assumption, these models have proved extremely powerful in predicting when co-operation between animals will evolve (Dugatkin & Reeve 1998; Maynard Smith 1982). As a result of this success, a vast literature has arisen on the evolution of co-operation, both theoretical and experimental. The size of this literature makes it difficult to give a concise account of how different models and experiments relate to one another. There is, however, an increasing consensus of how co-operation should be discussed in evolutionary biology (Clutton-Brock 2002; Foster et al. 2006; Lehmann & Keller 2006a, 2006b; West et al. 2007). In this chapter, I follow this consensus, and