This post is an addendum to a previous one, “The Enactive Approach to Agency” (if you are interested check that out first). There I described “operational closure”, which is a proposed basis for understanding the organizational structure underlying biological autonomy. In particular, I praised the way it abstracts from the more complicated features of self-production (autopoiesis) that characterize the living cell.
I have been re-reading Kate Nave’s excellent book The Drive to Survive: The Free Energy Principle and the Meaning of Life. In it, she criticizes the concept of operational closure as an inadequate basis for biological autonomy (even when coupled with the notion of precariousness). The shortcoming is precisely the fact that the framework doesn’t sufficiently capture an important self-producing feature of a system like the single-celled organism, specifically that whereby sub-cellular parts constantly re-compose themselves utilizing the flow of lower-scale inputs:
A metabolic self-producer is necessarily active and dependent on externally introduced inputs to replenish and refuel its continuation. It is this that makes a network of chemical reactions a self-producer, and it is this precarious dependence that is key to the bioenactive naturalization of goals, intentionality, and immanent teleology. (p. 151, emphasis original).
Nave notes that, since component parts of any sort will break down eventually, merely asserting their “precariousness” does not pick out what is distinctive to organisms. In the living cell, the organization is characterized by higher-scale structures that, requiring constant re-building, have a shorter life-cycle than the dynamical features displayed by the total organization. These depend on the ongoing activity of lower-scale (matter/energy) processes they encompass and channel for this rebuilding. For this reason, these higher-scale features can be labeled “constraints,” and this argues for a concept of network closure called “constraint closure” (an idea introduced in Moreno and Mossio, 2015). Nave endorses constraint closure as a better characterization of the phenomenon underlying biological autonomy (see discussion in Ch. 10).
This concept builds in a degree of hierarchy. Moreno and Mossio discuss this in terms of the distinction between the constraints and the “processes” they channel and depend on. Translating this using my preferred causal process framework (see my recent paper!) leads to the following picture. “Constraints” are also processes: specifically they are larger-scale composite causal processes where a pattern of interactions among constituents account for their distinctive causal powers. These include the ability to channel the activity of a collection of smaller adjacent processes. What is special are two features: first, that the faster-changing collection of relatively less attached (“constrained”) processes participate in interactions with the constituents of the larger composites in a way that sustains the latter. Second, of course, is that a collection of these larger (“constraining”) composite processes interact to form the kind of interdependent network familiar from the discussion of operational closure. As Nave emphasizes, the constraining processes are relatively stable compared to the processes they constrain, but of course on a longer timescale their continued coherence is highly fragile (unlike the parts of a machine).
To this picture one can add a model of how the system (as a whole) interacts with its environment. Here it seems that the dual-scale model of constraint closure lends itself well to understanding how it can respond to environmental changes. Changes that impact the network are accompanied by the ongoing rebuilding of constraints, and this allows for the possibility of rebuilding in a different way: this provides for adaptivity. Indeed, external impacts may cause some constraints to be destroyed, but their constituents might be used to build others: the system will persist as long as there is closure.
One feature that seems especially important is the character of the lower-scale processes in this picture. In a cell, these are microscopic (molecules or smaller). As such, they are incredibly fast-moving and noisy, which offers a basis for the larger-scale constraints to exploit their activity to change and adapt. The fact that living systems have roots in this indeterministic micro-world offers possibilities for persistance amid change that wouldn’t be available otherwise (see the discussion of spontaneity in the prior post).
There’s much to glean from the book, but I wanted to flag the case for positing “constraint closure” as the basis for the distinctive causal organization that underlies biological autonomy.
References
Moreno, A. & Mossio, M. 2015. Biological Autonomy: A Philosophical and Theoretical Inquiry. Dordrecht: Springer.
Nave, K. 2025. A Drive to Survive: The Free Energy Principle and the Meaning of Life. Cambridge: MIT Press.