Rosennean Complexity and its relevance to ecology

Complexity is not the same as complicatedness: a system is complicated if it has many components, but it is complex if it cannot be modelled as a machine and has emergent properties. The theoretical biologist Robert Rosen argued that living organisms are complex in this sense, and his (M, R) systems provide a description of a living organism in which the central point is that organisms are closed to efficient causation, which means that all the specific catalysts needed for the organism to maintain itself must be produced by the organism itself. This includes the catalysts needed to maintain the other catalysts. On the other hand an organism is not closed to material causation, because there must be a net overall irreversible process to provide the necessary thermodynamic driving force for metabolism. (M, R) systems are usually discussed in relation to individual organisms, but they can also be applied to interactions between different organisms, allowing analysis, for example, of how two or more species can exist in symbiotic relationships with one another, able to live together, but not separately. Application of Rosennean complexity to fields other than life is possible, as we discuss. Rosen's holistic vision of organisms, in which all components affect all others, has implications for the concepts of hierarchy and downward causation that are sometimes invoked in philosophical discussions, because it means that there is no hierarchy and no downward causation.