Motoo Kimura

(November 13, 1924 – November 13, 1994) was a Japanese biologist best known for introducing the neutral theory of molecular evolution in 1968. He became one of the most influential theoretical population geneticists. He is remembered in genetics for his innovative use of diffusion equations to calculate the probability of fixation of beneficial, deleterious, or neutral alleles. Combining theoretical population genetics with molecular evolution data, he also developed the neutral theory of molecular evolution in which genetic drift is the main force changing allele frequencies. James Franklin Crow, himself a renowned population geneticist, considered Kimura to be one of the two greatest evolutionary geneticists, along with Gustave Malécot, after the great trio of the modern synthesis, Ronald Fisher, J. B. S. Haldane, and Sewall Wright.

Life and work Kimura was born on November 13, 1924, in Okazaki, Aichi Prefecture. From an early age he was very interested in botany, though he also excelled at mathematics (teaching himself geometry and other maths during a lengthy convalescence due to food poisoning). After entering a selective high school in Nagoya, Kimura focused on plant morphology and cytology; he worked in the laboratory of M. Kumazawa studying the chromosome structure of lilies. With Kumazawa, he also discovered how to connect his interests in botany and mathematics: biometry

Due to World War II, Kimura left high school early to enter Kyoto Imperial University in 1944. On the advice of the prominent geneticist Hitoshi Kihara, Kimura entered the botany program rather than cytology because the former, in the Faculty of Science rather than Agriculture, allowed him to avoid military duty. He joined Kihara's laboratory after the war, where he studied the introduction of foreign chromosomes into plants and learned the foundations of population genetics. He received his PhD in 1956, before returning to Japan (where he would remain for the rest of his life, at the National Institute of Genetics). " models of mutation, all of which would be used widely as the field of molecular evolution grew alongside the number of available peptide and genetic sequences. The stepwise mutation model is a "ladder model" that can be applied to electrophoresis studies where homologous proteins differ by whole units of charge. An early statement of his approach was published in 1960, in his An Introduction to Population Genetics. He also contributed an important review article on the ongoing controversy over genetic load in 1961.

1968 marked a turning point in Kimura's career. In that year he introduced the neutral theory of molecular evolution, the idea that, at the molecular level, the large majority of genetic change is neutral with respect to natural selection—making genetic drift a primary factor in evolution. The field of molecular biology was expanding rapidly, and there was growing tension between advocates of the expanding reductionist field and scientists in organismal biology, the traditional domain of evolution. The neutral theory was immediately controversial, receiving support from many molecular biologists and attracting opposition from many evolutionary biologists.

Kimura spent the rest of his life developing and defending the neutral theory. As James Crow put it, "much of Kimura's early work turned out to be pre-adapted for use in the quantitative study of neutral evolution".

Though difficult to test against alternative selection-centered hypotheses, the neutral theory has become part of modern approaches to molecular evolution.

In 1992, Kimura received the Darwin Medal from the Royal Society, and the following year he was made a Foreign Member of the Royal Society.

Honors 1959 – Genetics Society of Japan Prize 1988 – International Prize for Biology 1992 – Darwin Medal 1993 – Foreign member of Royal Society