We propose a theoretical and formal way to account for the various levels of organization that biological systems may realize. Our key assumption is that levels of organization are to be understood as specific networks of interdependences among the functional constituents. More precisely, we will rely on the notion of organizational closure, which refers to the mutual construction and stabilization of constituents playing the role of constraints within the system. A level of biological organization, we will argue, is a level of closure of constraints.
With this characterization in hand, we will first discuss those situations in which different levels of organization can be distinguished, and hierarchically articulated, by relying on sharp discontinuities. In particular, this is the case of cells within multicellular organisms. We will then focus on those more complex cases in which the description of a level of organization requires appealing to the notion of “tendency to closure”, which aims to deal with the qualitative notion of level of organization by quantitative means. In particular, the tendency to closure involves a quantitative measure of functional interdependences at the relevant spatial scale at which constraints operate.
We conclude with a preliminary discussion of the spatiotemporal conditions (in particular: the dependence on large space scale and small time scale) that enable the coherence of organisms realizing high levels of organization (e.g. mammals).