Self-reproducing system can behave as Maxwell's demon: theoretical illustration under prebiotic conditions.

The recent discovery of polymerase activity in a ribosomal RNA intervening sequence as well as other studies of RNA-replicating systems suggest that the first living molecules were RNAs called replicases. According to this suggestion from biochemical studies, the replicase system is chosen as the simplest case of self-reproducing systems, and the fundamental problem of "what is life" is theoretically investigated by analysing the behavior of a replicase system with a supply of organic materials under prebiotic conditions. In this analysis, it is essential to consider (i) self-reproduction on the basis of its own information, (ii) maintenance and improvement of the information by selection and (iii) environmental event of non-biologically generating organic materials from inorganic matter by photochemical reactions, probably occurring in prebiotic conditions on the Earth. The replicases can retain and further elevate their self-reproducibility through competition among their descendant mutants for acquiring a limited quantity of materials, if the initial ability of self-reproduction and the concentration of replicases are above some critical values. By this selection, the replicase molecules retain a narrowed range of nucleotide sequences, or a state of lower entropy, against the natural tendency of sequence divergence, but this entropy reduction is sufficiently compensated by the entropy production in the environmental event of energy conversion from photons to heat. Once the stability of a self-reproducing system is established in the above sense, the self-reproducing system can operate as Maxwell's demon to regulate the outside flow of matter by its catalytic function without any contradiction to the second law of thermodynamics.