Abstract/Summary

Common sense tells us that biological systems are goal-directed, and yet the concept remains philosophically problematic. We propose a novel characterization of goal-directed activities as a basis for hypothesising about and investigating explanatory mechanisms. We focus on survival goals such as providing adequate nutrition to body tissues, highlighting two key features – normativity and action. These are closely linked inasmuch as goal-directed actions must meet normative requirements such as that they occur when required and not at other times. We illustrate how goal-directed actions are initiated and terminated not by environmental features and goals themselves, but by markers for them. For example, timely blood clotting is the essential response to injury, but platelet activation, required for clotting, is initiated not by the injury itself but by a short sequence of amino acids (GPO) that provides a reliable marker for it. We then make the case that the operation of markers is a prerequisite for common biological phenomena such as mistake-proneness and mimicry. We go on to identify properties of markers in general, including those that are genetically determined, and those which can be acquired through associative learning. Both provide the basis for matching actions to changing environments and hence adaptive goal-directedness. We describe how goal-directed activities such as bird nest construction and birdsong learning, completed in anticipation of actions in the environment, have to be evaluated and practised against a standard of correctness. This characterization of goal-directedness is sufficiently detailed to provide a basis for the scientific study of mechanisms.