Abstract

Even the simplest cell exhibits a high degree of functional differentiation (FD) realized through several mechanisms and devices contributing differently to its maintenance. Searching for the origin of FD, we briefly argue that the emergence of the respective organizational complexity cannot be the result of either natural selection (NS) or solely of the dynamics of simple self-maintaining (SM) systems. Accordingly, a highly gradual and cumulative process should have been necessary for the transition from either simple self-assembled or self-maintaining systems of functionless structural components to systems with FD. We follow results of recent in vitro experiments with respect to competition among protocells, where a primitive type of selection begins to operate among them accompanied by a parallel evolution of their functional domain. We argue that minimal forms of FD should be established within the evolution of SM processes in protocells as they undergo a simpler selection process for stability and persistence in a prebiotic environment. We then suggest the concept of closure of constraints (CoC) as a way to identify and describe minimal FD in a far-from-equilibrium SM organization. We show in detail how the concept of CoC together with the conditions for its fulfillment can be applied in the case of a simple protocellular system that begins to couple internal chemical reactions with the formation of its membrane components. Finally, we discuss how such SM systems can evolve towards significantly higher levels of FD, suggesting this is mainly the result of functional recombination (formation of mechanisms) in the context of a modular SM organization.