Kimura, Motoo (1924– )

Japanese biologist who, as a result of his work on population genetics and molecular evolution, has developed a theory of neutral evolution that opposes the conventional neo-Darwinistic theory of evolution by natural selection.

Kimura was born in Okazaki, near Nagoya, and studied at Kyoto and in the USA at Iowa State and Wisconsin universities. He spent most of his career at the National Institute of Genetics in Mishima, starting in 1949 and becoming head of the Department of Population Genetics in 1964.

Kimura began in 1968 the work that was to lead to the theory of neutral evolution. Comparing the amino acid compositions of the alpha and beta chains of the haemoglobin molecules in humans with those in carp, he found that the alpha chains have evolved in two distinct lineages, accumulating mutations independently and at about the same rate over a period of some 400 million years.

According to Kimura's theory, evolutionary rates are determined by the structure and function of molecules, and most variability and evolutionary change within a species is caused by the random drift of mutant genes that are all selectively equivalent and selectively neutral. Kimura's theory denies that the environment influences evolution and that mutant genes confer either advantageous or disadvantageous traits.