The primary purpose here has been to review and contrast the notions of autopoiesis and collective autocatalysis. This has resulted in a focus on the autopoietic requirement for spatial localization or confinement to itself be a product of the reaction network. I have attempted to make this criterion as clear as possible by proposing a specific heuristic test. In essence this says that the critical test should not merely involve the ability of an entity to discriminate or demarcate itself from some sort of relatively disorganized background. Rather, it should require the ability for an agent to discriminate itself from other, spatially adjacent, but organizationally identical, agents. In particular, although it is not an integral element of the autopoietic concept, it seems to me that for agents to serve as actors in a Darwinian selective process, it is essential that they should be capable of this minimal ``individuation''.
In reviewing a number of abstract models of biological organization, I have tried to bring out the fact that--as envisaged by Kauffman--the emergence of collective autocatalysis seems to be relatively easy or robust. Systems with wildly different underlying architectures seem to exhibit this phenomenon, corroborating the claim that the conditions for its appearance are relatively weak. On the other hand, it seems that none of these systems should qualify as exhibiting properly autopoietic organization--including even the SCL system which was specifically concepted as an exemplar of autopoiesis.
It is not clear to me whether this is merely because these systems have not (with the obvious exception of SCL) been designed with this end in mind; or because autopoietic organization is, in fact, a fundamentally more elusive phenomenon than collective autocatalysis. I would welcome discussion on the question.
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