The Evolutionary Theory along the Phylogenetic Tree of Unicellular Organisms

Abstract

In parallel to the advancement of molecular biology suggesting the evolutionary route from the RNA world to the DNA-RNA-protein world through the RNA-protein world, the analysis on the nucleotide base changes in ribosomal RNA genes revels that the divergence of prokaryote and eukaryote first occurred in the DNA-RNA-protein world but the divergence of present-day lineages in eukaryotes occurred after the ancestral eukaryote has acquired the mitochondria as the endosymbionts of O2-respiratory eubacteria. These results strongly suggest that the divergence of unicellular organisms is closely related with the drastic changes in cell contents such as the formation of ribosome, the generation of RNA genes, the conversion from the RNA genes to DNA genes, gene duplication or the endosymbiosis. In the present paper, such drastic changes in evolution of unicellular organisms are theoretically formulated on the basis of the concept of biological activity which consists of the acquired energy, stored energy and systematization. Upon the drastic change in cell contents, the biological activity of an organism is first lowered by the increase in stored energy, but it is gradually recovered as the systematization advances to increase the acquired energy overcoming the increased stored energy and negative entropy due to the systematization itself. Throughout this process, the divergence of new style organisms occurred utilizing new material and energy sources. Such evolutionary process will be explained in detail at the main divergence points in the phylogenetic tree. The relation of such drastic changes in evolution with Darwinian evolution is also clarified.