III.8 Evolution apparently optimized the frequency of spontaneous mutations
Experimental results have shown that evolution has “tuned” the ratio of the repair and replication activities of DNA-polymerase in the individual groups of organisms to achieve the optimum frequency of mutations from an evolutionary and functional standpoint (Cox 1976).The consequent frequency of mutations is not very high, so that the organisms and populations are not exposed to an excessive mutation burden, but not too low, so that species do not stagnate evolutionarily and can adapt to changing conditions.Experimentally, it is possible to select a line of bacteria with a much lower mutation rate (Radman, Taddei, & Matic 2000).
It is interesting and very important from a theoretical standpoint that the number of nonsynonymous substitutions/genomes related to the generation time is very similar for the most varied groups of organisms (Drost & Lee 1995)and is not related to the size or metabolic activity of the particular species.As the number of synonymous substitutions/genomes related to the generation time or the number of nonsynonymous substitutions/genomes related to the number of divisions or to the time, to the contrary, differs substantially for various types of organisms (Bromham, Rambaut, & Harvey 1996), it is probable that the present-day frequency of mutations was optimized from the standpoint of the rate of evolution and not from the standpoint of (energetic) “costs” and “profits” (Sniegowski et al. 2000). It is most certainly not determined only by physical or chemical laws valid for DNA replication, for example, the number of tautomeric transitions.