On the Origin of Genes

The character of a present-day organism is determined by the set of genes. Thus, the origin of genes is one of the most important problems in the origin of life. From the aspect of the second law of thermodynamics, some systematic force is needed to produce such special arrangement of nucleotide bases as genes. In the present paper, such systematic force is proposed to be the selection acting on self-reproduced cells. As a molecular fossil of the self-reproduction of the primitive cell before the appearance of the ribosome, it is indicated in the prokaryotes that the polypeptide of a cell wall element is formed as the mixture of L- and D-types of amino acid residues by the catalytic actions of proteins and the matured element is transferred to the outside across the membrane by the orientation change of a lipid derivative bound to the element. This strongly suggests that the self-reproduction of a primitive cell has started from the antagonistic balance between lipid synthesis and cell wall construction. At this early stage, some of the RNAs contained in the cell would have catalyzed the polymerization of amino acids and some of the random sequences of polypeptides would have catalyzed the replication of RNAs and others catalyzed the lipid synthesis and cell wall construction. The self-reproducing cells obey the equation of replicator dynamics containing the change term. This equation not only shows Darwinian evolution that selects the nucleotide base changes upon the replication of RNAs to raise the increase rate of the cell but also leads to the convergence of RNA contents to the translation apparatus and RNA genes of proteins through the intermediate variant cells with the increase rate transiently lowered by the interference between RNAs. Lastly, the innovation process from such self-reproducing cells in the RNA-protein world to the present-day organisms is also briefly summarized.