Motoo Kimura

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Motoo Kimura

Motoo Kimura.jpg
Born(1924-11-13)November 13, 1924
Okazaki, Japan
Died13 November 1994(1994-11-13) (aged 70)
Alma materUniversity of Wisconsin
Known forNeutral theory of molecular evolution
SpouseHiroko Kimura
Scientific career
InstitutionsNational Institute of Genetics
ThesisStochastic Processes in Population Genetics (1956)
Doctoral advisorJames F. Crow
Other academic advisors
InfluencesSewall Wright
InfluencedTomoko Ohta

Motoo Kimura (木村 資生, Kimura Motō) (November 13, 1924 – November 13, 1994) was a Japanese biologist best known for introducing the neutral theory of molecular evolution in 1968.[2][3] 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.[4] 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.[5] James F. 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.[6]

Life and work[edit]

Kimura was born on November 13, 1924 in Okazaki, Aichi Prefecture.[7] 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.[1]

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.[7][1]

In 1949, Kimura joined the National Institute of Genetics in Mishima, Shizuoka. In 1953 he published his first population genetics paper (which would eventually be very influential), describing a "stepping stone" model for population structure that could treat more complex patterns of migration than Sewall Wright's earlier "island model". After meeting visiting American geneticist Duncan McDonald (part of the Atomic Bomb Casualty Commission), Kimura arranged to enter graduate school at Iowa State College in the summer 1953 to study with J. L. Lush.[1]

Kimura soon found Iowa State College too restricting; he moved to the University of Wisconsin to work on stochastic models with James F. Crow and to join a strong intellectual community of like-minded geneticists, including Newton Morton and most significantly, Sewall Wright. Near the end of his graduate study, Kimura gave a paper at the 1955 Cold Spring Harbor Symposium; though few were able to understand it (both because of mathematical complexity and Kimura's English pronunciation) it received strong praise from Wright and later J.B.S. Haldane.[1][7]

His accomplishments at Wisconsin included a general model for genetic drift, which could accommodate multiple alleles, selection, migration, and mutations, as well as some work based on R.A. Fisher's fundamental theorem of natural selection. He also built on the work of Wright with the Fokker–Planck equation by introducing the Kolmogorov backward equation to population genetics, allowing the calculation of the probability of an allele to become fixed in a population.[8] 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).[1]

Kimura worked on a wide spectrum of theoretical population genetics problems, many of them in collaboration with Takeo Maruyama. He introduced the "infinite alleles", "infinite sites", and "stepwise[9]" 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.[10] He also contributed an important review article on the ongoing controversy over genetic load in 1961.[1][11]

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.[12][13] 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.[14][12]

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".[1] As new experimental techniques and genetic knowledge became available, Kimura expanded the scope of the neutral theory and created mathematical methods for testing it against the available evidence.[14] Kimura produced a monograph on the neutral theory in 1983, The Neutral Theory of Molecular Evolution, and also worked to promote the theory through popular writings such as My Views on Evolution, a book that became a best-seller in Japan.[15]

Though difficult to test against alternative selection-centered hypotheses, the neutral theory has become part of modern approaches to molecular evolution.[16][17]

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.[1]

Kimura suffered from progressive weakening caused by amyotrophic lateral sclerosis later in life.[6] In an accidental fall at his home in Shizuoka, Japan, Kimura struck his head and died on November 13, 1994, of a cerebral hemorrhage.[7][18][6] He was married to Hiroko Kimura. They had one child, a son, Akio, and a granddaughter, Hanako.[19][20]


See also[edit]


  1. ^ a b c d e f g h i j Crow, J. F. (1997). "Motoo Kimura. 13 November 1924–13 November 1994: Elected For.Mem.R.S. 1993". Biographical Memoirs of Fellows of the Royal Society. 43: 255–265. doi:10.1098/rsbm.1997.0014. S2CID 44725944.
  2. ^ Kimura, Motoo (1968). "Evolutionary rate at the molecular level" (PDF). Nature. 217 (5129): 624–626. Bibcode:1968Natur.217..624K. doi:10.1038/217624a0. PMID 5637732. S2CID 4161261.
  3. ^ Nei, M. (1995). "Motoo Kimura (1924–1994)". Molecular Biology and Evolution. 12 (5): 719–722. Bibcode:1995JMolE..40..709J. doi:10.1093/oxfordjournals.molbev.a040250. PMID 7476119.
  4. ^ Watterson, G. (1996). "Motoo Kimura's Use of Diffusion Theory in Population Genetics". Theoretical Population Biology. 49 (2): 154–188. doi:10.1006/tpbi.1996.0010. PMID 8813021.
  5. ^ Ohta T. and Gillespie J.H. (1996). "Development of neutral and nearly neutral theories". Theoretical Population Biology. 49 (2): 128–142. CiteSeerX doi:10.1006/tpbi.1996.0007. PMID 8813019.
  6. ^ a b c d e f g h i Crow, James F. (1995). "Motoo Kimura (1924–1994)". Genetics. 140 (1): 1–5. Bibcode:1995JMolE..40..709J. doi:10.1007/BF00160522. PMC 1206539. PMID 7635277.
  7. ^ a b c d Ohta, Tomoko (December 1996). "Motoo Kimura". Annual Review of Genetics. 30 (1): 1–5. doi:10.1146/annurev.genet.30.1.1. ISSN 0066-4197. Retrieved 27 February 2023.
  8. ^ Kimura, Motoo (1986). "Diffusion Models of Population Genetics in the Age of Molecular Biology". In Gani, J. (ed.). The Craft of Probabilistic Modelling. Springer. pp. 150–165. doi:10.1007/978-1-4613-8631-5_10. ISBN 0-387-96277-8.
  9. ^ Kimura, M.; Ohta, T. (1978-06-01). "Stepwise mutation model and distribution of allelic frequencies in a finite population". Proceedings of the National Academy of Sciences of the United States of America. 75 (6): 2868–2872. Bibcode:1978PNAS...75.2868K. doi:10.1073/pnas.75.6.2868. ISSN 0027-8424. PMC 392666. PMID 275857.
  10. ^ Kimura Motoo, Shūdan Idengaku gairon, Baifūkan, Tokyo 1960
  11. ^ Kimura, M (1961). "Some calculations on the mutation load". Jpn. J. Genet. 36: 179–190.
  12. ^ a b Ohta, Tomoko (November 1992). "The Nearly Neutral Theory of Molecular Evolution". Annual Review of Ecology and Systematics. 23 (1): 263–286. doi:10.1146/ ISSN 0066-4162. Retrieved 28 February 2023.
  13. ^ Kimura, Motoo (1983). The neutral theory of molecular evolution. Cambridge University Press, 1968. ISBN 978-0-521-23109-1.
  14. ^ a b Crow, James F. (1 December 2008). "Mid-Century Controversies in Population Genetics". Annual Review of Genetics. 42: 1–16. doi:10.1146/annurev.genet.42.110807.091612. Retrieved 28 February 2023.
  15. ^ Kimura, Motoo (1988). Seibutsu shinka wo kangaeru (My views on evolution) (in Japanese). Iwanami Shoten.
  16. ^ Nei, Masatoshi (1987). Molecular Evolutionary Genetics. Columbia University Press.
  17. ^ Crow, J. (1996). "Memories of Motô". Theoretical Population Biology. 49 (2): 122–127. doi:10.1006/tpbi.1996.0006. PMID 8813018.
  18. ^ "Motoo Kimura; Japanese Geneticist, 70". The New York Times. November 16, 1994.
  19. ^ Steen, T. Y. (1996). "Always an eccentric?: A brief biography of Motoo Kimura". Journal of Genetics. 75: 19–01. doi:10.1007/BF02931748. S2CID 29545568.
  20. ^ Brenner's Encyclopedia of Genetics, 2nd Edition[1]
  21. ^ "John J. Carty Award for the Advancement of Science". National Academy of Sciences. Archived from the original on 29 December 2010. Retrieved 25 February 2011.
  22. ^ Royal Society: archived record