The Evolution of Agency

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Abstract: Biology has largely ignored the most salient property of living organisms, which is that they do things. Things don’t just happen to them, or in them – they behave actively and purposefully, as autonomous agents in the world. The modern trend of reductionism dismisses this purposiveness as an illusion, with the real causality ultimately residing at the level of atoms and molecules, the interactions of which are determined by basic physical forces. This mechanistic reductive determinism has been preferred to the supposed alternatives of vitalism and dualism. But these are not our only choices. It is possible to construct a non-reductive physicalist framework to explain how agency and causal power can emerge from the very specific kind of organisation of matter that characterises life. Fundamental indeterminacy in the universe means that the next physical state of a system is not fully determined by the current physical state. In the nervous system, this indeterminacy creates causal slack and provides an opening for higher-order properties – meaning, purpose, and value – inherent in the states of the system to have real causal power, to settle the outcome. That causal power does not come for free – it is packed into the organism through evolution, through development, and through learning. It is encoded into the genome and embodied in the physical structure of the nervous system in the strength of synaptic weights that express functional criteria in relation to a hierarchy of aims of the organism. These criteria can be accessed via conscious mental processes and changed on the fly based on current needs and goals. This gives a physical basis by which decisions are made in real time, not just as the outcome of complex physical interactions, but for reasons – a firm footing for the otherwise troublesome concept of mental causation. Collectively, this framework sketches an explanation for how a complex system can become a self, an autonomous agent imbued with causal power, capable of acting in the world to further its own aims. By tracing the elaboration of these capacities over evolution, it is possible to naturalise concepts of meaning and purpose and thus ground our understanding of our own capacity for free will.