On the relations between behaviour, mechanism, and environment : explorations in artificial evolution

This thesis presents an externalist exploration of the relations between behaviour, mechanism, and environment, as they arise in a variety of agent-environment systems. It offers contributions at conceptual, methodological, and empirical levels of discourse. Externalism describes the attempt to understand the internal in terms of the external, and the thesis begins by developing a conceptual framework justifying the use of artificial evolution models in the application of this perspective to agent-environment systems. In particular, it is argued that such models play a crucial role in elaborating the distinction between behavioural and mechanistic levels of description. There follows a series of models, of both game-theoretic and evolutionary-robotic character, which focus on explaining internal ‘complexity’ in terms of adaptation to (external) environmental variability. As part of this project, accounts of the ‘evolution of complexity’ in general are critiqued, and the practical importance of noise in artificial evolution is discussed. The thesis continues with an integration of this externalist project with the well established theoretical biology methodology of ‘optimal foraging theory’. A novel methodology ‘individualbased optimal situated modelling’ is described, which extends orthodox optimal foraging theory through (1) the use of artificial evolution as an optimisation procedure and, (2) modelling agentenvironment interaction at the level of situated perception and action. The conceptual leverage afforded by this extension is illustrated in its application to the problem of behaviour coordination in a simple agent-environment system; for example, the need for a dedicated ‘action selection mechanism’ is questioned. The methodology is then addressed to a range of issues in contemporary theoretical biology and psychology: the ‘interference function’, the ‘ideal free distribution’, and the ‘individual matching law’, issues which are united by a concern with individual choice and its collective consequences. A series of models are presented which demonstrate, in these contexts, that (1) behaviours for which there is debate about the level of complexity required for their underlying mechanism, can be subserved by surprisingly simple mechanisms, and (2) behaviours which may be irrational when expressed by an isolated individual can be understood as rational in a group context. Submitted for the degree of D. Phil. University of Sussex