Motoo Kimura achieved international recognition for his numerous contributions to the fields of evolution and population genetics. He is considered the founder of the neutral theory of molecular evolution. According to this theory, evolutionary change and most of the variability within a species are caused at the molecular level by the random drift of mutant genes. By comparison, English naturalist Charles Darwin's theory of natural selection was based on the concept that evolution occurs at the species level, with those individuals best adapted to the environment most fit to survive. Kimura focused on the molecular changes that occur in the nucleotides of DNA, and concluded that the resulting mutant genes are neutral and subject to random drift, or changes, in gene frequencies due to pure chance. Kimura developed his theory quantitatively and thus, according to James F. Crow, writing in Population Genetics and Molecular Evolution, "laid a very...