Evolution, Selection and the Metabolic Foundations of the RNA World

The chemoton model of cells posits three sub-systems: metabolism, compartmentalization and information (Gánti, 2003). This paper describes a specific model for the evolution of a reproducing system with rudimentary versions of these three inter-dependent sub-systems. This is based on the initial emergence and reproduction of autocatalytic networks in hydrothermal micro-compartments containing iron sulfide. The driving force for life is catalysis of the dissipation of the intrinsic redox gradient of the planet (Russell and Kanik, 2010). The initial proto-metabolism was based on positive feedback loops associated with in situ carbon fixation in which the initial proto-metabolites modified the catalytic capacity and mobility of metal-based catalysts, especially iron-sulfur centres. A number of selection mechanisms, including catalytic efficiency and specificity, hydrolytic stability and selective solubilization, are proposed as key determinants for autocatalytic reproduction exploited in proto-metabolic evolution. This evolutionary process leads from autocatalytic networks within pre-existing compartments to discrete, reproducing, mobile vesicular protocells with the capacity to use soluble sugar phosphates and hence the opportunity to develop nucleic acids. Fidelity of information transfer in the reproduction of these increasingly complex autocatalytic networks is a key selection pressure in prebiological evolution that eventually leads to the selection of nucleic acids as a digital information sub-system and hence the emergence of fully functional chemotons capable of Darwinian evolution.