Evolutionary developmental biology has long challenged the view that the supply of phenotypic variation has little evolutionary efficacy. Central to this challenge is the claim that biases and constraints in the supply of variation exist and do alter the outcomes of the evolutionary processes. Amongst those interested in morphological evolution this challenge has led to a reconsideration of the role of phenotypic variation in morphological evolution. A new understanding of the evolution of morphology which takes into account contingency and development has resulted. Interestingly, in behavioural biology very little attention has been paid to analogous issues relating to behavioural evolution. Yet, there is no theoretical or empirical reason for this apparent omission. Motivation for consideration of the role of phenotypic variation in behavioural evolution is even stronger than that available for morphology. There are clear sources of extra-genetic behavioural inheritance which carry with them bias and constraint, for example social learning, niche construction and genetic accommodation. The supply of variation is thus central to understanding this evolutionary domain. My doctoral thesis argues for two key conclusions. (1) That there is sufficient empirical and theoretical evidence to motivate the consideration of the supply of phenotypic variation in investigations of the evolution of behaviour. A natural starting point for such a consideration is the existing conceptual framework provided by evolutionary developmental biology. And, (2) In considering behavioural evolution from an evolutionary developmental biology perspective it becomes apparent that some sources of behavioural phenotypic variation represent unique ways of affecting the evolvability of a lineage. Understanding these sources of evolvability is an essential element of evolutionary behavioural biology.