Beyond Genes and Environments: Indirect Genetic Effects and the Evolution of Behaviour

This chapter focuses on a related but less widely recognized phenomenon, indirect genetic effects (IGEs), that also blurs the traditional distinction between genetic and environmental effects. It focuses primarily on IGEs affecting the expression of behavioural traits and provides a discussion on IGEs arising from interactions among unrelated individuals. The chapter provides a brief introduction to traditional quantitative genetic theory. It shows how the quantitative genetic theory can be extended to include social interactions and illustrates what consequences this has for the evolution of behaviour. IGEs represent an additional source of genetic variance for behaviours that change our expectations, relative to those derived from direct genetic effect (DGE)-only models, of phenotypic responses to selection. A common outcome of most theoretical models is that IGEs will influence the evolutionary dynamics of phenotypic traits involved in the social interactions.