The Nearly Neutral Theory of Molecular Evolution

摘要

The neutral theory of molecular evolution was put forward by M.Kimura.The neutral theory proposes that the evolution of genes is by random genetic drift and not by selection.In this theory,new mutations are classified into deleterious,neutral and advantageous classes.I realized that the intermediate class of mutations between the selected and neutral classes must be important and,in 1973,proposed the nearly neutral theory of molecular evolution.The nearly neutral theory emphasizes the interaction of drift and selection.With the rapidly increasing availability of genome data,the applicability of the nearly neutral theory is expanding.In this report,I review recent progress on the applicability of the nearly neutral theory in relation to the evolution of complex systems,at the following two levels:(1) Protein coding regions:The most important prediction of the nearly neutral theory is the rapid evolution of species with a small population size compared with those with a large population size.This prediction has been verified by comparative studies of synonymous and nonsynonymous substitutions among various species.Further,DNA polymorphism data for various species show a preponderance of slightly deleterious mutations.