5 A Heuristic Test

I have suggested that (molecular) autopoiesis and collective autocatalysis are closely related ideas. Both involve something like a self-sustaining reaction network, and both require some mechanism of spatial localization or confinement for effective operation. The critical distinction is that autopoiesis specifically requires that this confinement should itself be in some sense a product of the confined reaction network, whereas collective autocatalysis is assumed to rely on some independent confinement mechanism.

This seems to me clear enough as far as it goes; but I still have some difficulty in deciding whether the full requirement of autopoiesis is met in particular cases. Specifically, consider the computer model system offered by Varela et al. (1974). It is true that, in this case, there is a cleavage of the space which confines the reaction network, and which is maintained as a specific consequence of the reaction network. However, it is also true that, as an integral aspect of the ongoing behaviour of this autopoietic system, the spatial boundary or membrane is regularly ruptured. The membrane is subsequently repaired again--and, indeed, this is arguably the chief phenomenon of interest in this system. Nonetheless, the fact that the spatial localization is regularly interrupted in this way makes it more difficult to be clear what exactly the ``topological'' autopoietic requirement or criterion is.

So I would like to suggest the following informal and heuristic test. Consider two instances of the same collectively self sustaining reaction network. For the moment I suppose that we do not know whether these should qualify as autopoietic or (merely) collectively autocatalytic. They are considered as instances of the same reaction network in the sense that the same set of molecular species is present in both cases; but they are separate instances in the sense that each is constituted (instantaneously) by distinct collections of individual molecules. Specifically I assume that, initially, they have been prepared or instantiated in separate reaction ``vessels'' (in the manner of the independent confinement mechanism already posited to support the continued operation of a collectively autocatalytic set). Now consider the situation if the contents of both vessels are ``mixed'' together. I assume that there will be continued availability of any necessary food set materials etc., so that the self-sustaining behaviour of the network(s) can continue unchanged. The key question now is whether there will still meaningfully be two instances of the reaction network or just one. That is, in the absence of any imposed spatial separation mechanism, do the networks themselves maintain their individuality? I would suggest that, if they do, then this reaction network may reasonably be classified as meeting the autopoietic criterion ``for specifying the topological domain of its realization''; whereas if not, then the network should be regarded only as collectively autocatalytic.

mcmullin@eeng.dcu.ie