Every body’s gotta eat: why autonomous systems can’t live on prediction-error minimization alone

Abstract

Karl Friston’s Free Energy Principle has been proposed as a definition of existence from which “everything of interest about life and the universe can be derived” (Friston, 2019, p.176). Despite pretensions to a theory of every ‘thing’, focus has largely been on the first of these and the attempt to “unify all adaptive autopoietic and self-organizing behaviour under one simple imperative; avoid surprises and you will last longer” (Friston, 2012, p.2).

By analysing biological existence in terms of the stability of a set of essential variables and relations that are taken to define a particular organism, then redescribing this stability amid perturbation in statistical terms as ‘surprisal-minimization’, the FEP proposes to connect this biological imperative up to an account of higher-level cognition as involving the operation of hierarchical predictive models. At first glance then, it appears the ideal partner to the bioenactivist seeking to ground the content of our mental lives in this basic, biological intentionality.

The potential compatibility is misleading. By reducing autonomy to the kind of stability amid perturbation that could be shared by pendulums and people alike, the FEF makes no distinction between a homeostatic mechanism and a self-producing agent, thereby failing to account for why the latter alone should be credited with active engagement in its own continuation. The free energy theorist is left to choose between instrumentalism about intentional attribution, or mathematically-motivated animism.

Neither is an option for the bioenactivist who seeks a naturalistic account of intentionality and immanent teleology as real features distinct to living systems alone. This does not, however, mean that the FEP has inadvertently undermined the bioenactivist program by revealing there to be no difference in kind between life and non-life. The problem lies instead in its underlying assumption of a machine-substantialist ontology, which erases this distinction from the get-go by presuming the existence of a thing can be reduced to a set of invariant parts and the invariant rules that govern its dynamics.

Organisms are constrained by neither. Unlike machines, we not only persist through but depend upon both material turnover and unprestatable change in our space of possible behaviours. This, as a number of theoretical biologists and complexity scientists have argued, makes it impossible to derive any invariant form or equations that could fix the possible trajectories of a living system in advance. The failure of the FEF as a theory of life is not just due to the inadequacy of surprisal-minimization as a particular principle, but due to the broader inappropriateness of a machine-substance ontology for analysing biological existence.

The FEF’s failure is not the bioenactivist’s victory. For this we need to establish not only that living systems are different from machines, but also to show how these differences grant the former alone the status of intentional agents. The prevailing enactivist definition of autonomy as operational closure among precarious processes does not achieve this, for it fails to capture the mutual dependence between structure and dynamics that characterizes the self-determination of organisms. Instead, I draw upon Montévil, Moreno, and Mossio’s account of closure among constraints, to show how this describes a system that is intrinsically active in seeking out a continual supply of energy with which to rebuild the network of constraints that both embody that system and which would irretrievably disintegrate without such activity. Only such systems, I argue, can truly be said to have their own existence as the goal of their operations.

This will likely not convince the eliminativist, determined to reduce subjectivity to atoms and the void, nor the anthropocentrist who jealously withholds agency to his species alone. But for the person who feels that there is a vital difference between her strivings and the operations of a machine, I believe that the place to look is not in the rational powers that might set us apart from our humbler biological relations, but in the peculiar form of precariousness that we share.