Hylomorphism and the Metabolic Closure Conception of Life
This paper examines three exemplary theories of living organization with respect to their common feature of defining life in terms of metabolic closure: autopoiesis, (M, R) systems, and chemoton theory. Metabolic closure is broadly understood to denote the property of organized chemical systems that each component necessary for the maintenance of the system is produced from within the system itself, except for an input of energy. It is argued that two of the theories considered-autopoiesis and
... M, R) systems-participate in a hylomorphist pattern of thinking which separates the "form" of the living system from its "matter." The analysis and critique of hylomorphism found in the work of the philosopher Gilbert Simondon is then applied to these two theories, and on the basis of this critique it is argued that the chemoton model offers a superior theory of minimal life which overcomes many of the problems associated with the other two. Throughout, the relationship between hylomorphism and the understanding of living things as machines is explored. The paper concludes by considering how hylomorphism as a background ontology for theories of life fundamentally influences the way life is defined. Keywords: hylomorphismautopoiesis -(M, R) systemschemotonmetabolic closure -Simondonmachine   (2010), and others have gathered various theories together under this category. 4 They include: autopoiesis (Maturana and Varela 1980), (M, R) systems (Rosen 1991), the chemoton (Gánti 2003), the hypercycle (Eigen and Schuster 1977), autocatalytic sets (Kauffman 1993), RAF sets (Hordijk and Steel 2004), and others. Broadly speaking, metabolic closure may be defined as the property of metabolic systems, consisting of the transformation and degradation of chemical components, that each metabolite or enzyme needed for the maintenance of the system is produced by the system itself, apart from an influx of energy. In a system of metabolic closure, an initial source of energy is transformed along a series of chemical reactions that are organized in a circular pattern, the products of one reaction being the reactants for the next, allowing the system to persist in time. A metabolism without the structure provided by closure, by contrast, would remain a type of chemical "dissipative structure" as described by nonequilibrium thermodynamics, whose structure is imposed and maintained by the system's boundary conditions. 5 The property of closure in a metabolic system allows it to maintain its own structure and grants it a degree of autonomy and cohesion that is not found in other physical systems. To conceive of this property as the most fundamental feature of life is to argue, in effect, that reproduction or replication (and hence evolution) should be considered the achievement of a system that survives long enough to reproduce itself, or to develop the capacity to do so. This metabolic closure conception of life also generally makes little to no reference to macromolecular structure, to DNA or RNA, nor to any specific biomolecules, nor for that matter to any determinate "matter." Instead, it postulates that the essence of life is to be found in the "form" of its organization, which may be multiply realized in many different material substrata. In this respect, it draws on hylomorphism as a background ontology. 6 Hylomorphism in conceptions of life tends to arise from the combined refusal to reduce life to its material substratum and the recognition that life cannot be any type of thing or substance distinct from matter: instead, life is to be found in the form or organization of the material substratum. In the models of metabolic closure that we will consider, abstracting from the matter in favor of the form allows for highly general and compact definitions of life. At the same time, for this reason, the models tend to be formalistic and abstract, and far removed 4 The system-theoretic concept of "closure," used to differentiate levels of organization in nature, has also appeared in the literature with increasing frequency, being the theme of a relatively recent international workshop. Cf. Chandler and Van de Vijver (2000). 5 Cf., e.g., the discussion of the Belousov-Zhabotinsky reaction in Prigogine and Nicolis (1977). 6 The distinction between information and matter, which has often been used to distinguish living from nonliving systems, has rightly been recognized as being involved in a kind a modern hylomorphism (cf. Oyama 2000: 1), but the same also holds for the distinction between organization and matter as it tends to be used in fundamental theories of life.