A century after Darwin’s theory, the molecular biologists initiate to deal with evolution at the level of proteins and DNA (deoxyribonucleic acid) molecules and have come across and recognized another aspect of the evolutionary process called Neutral Molecular Evolution, which does not include natural selection. Knowledge of neutral molecular evolution is essential to understand how genes change ultimately. The neutral theory of molecular evolution suggests that most mutations in DNA or amino acid replacements among species are functionally neutral or nearly neutral and set by unsystematic genetic drift. The theory of neutrality proposes a baseline probability how DNA should modify eventually when natural selection is not present.
Earlier to neutral theory, evolutionary biologists believed that all changes are because of natural selection. When molecular data is not present, mutations were considered of as useful or harmful. It was not easy to consider that alteration of a very particular enzyme, for instance possibly be neutral. An in-depth knowledge of genetic code and the molecular basis for mutation and function of the protein, approach the amazing recognition that neutral or nearly neutral mutations may possibly occur. The neutral theory created especially the revolutionary idea that evolution of the neutral genes by genetic drift was not only feasible but frequent. The most amino acid variations among the species will not takes place by means of natural selection of adaptive difference except due to genetic drift of neutral alleles.