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(November 13, 1924 – November 13, 1994) was a Japanese
biologist A biologist is a scientist who conducts research in biology. Biologists are interested in studying life on Earth, whether it is an individual cell, a multicellular organism, or a community of interacting populations. They usually specialize ...
best known for introducing the
neutral theory of molecular evolution The neutral theory of molecular evolution holds that most evolutionary changes occur at the molecular level, and most of the variation within and between species are due to random genetic drift of mutant alleles that are selectively neutral. The ...
in 1968. He became one of the most influential theoretical
population geneticists Population genetics is a subfield of genetics that deals with genetic differences within and between populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as adaptation, speciation, and popu ...
. He is remembered in genetics for his innovative use of
diffusion equation The diffusion equation is a parabolic partial differential equation. In physics, it describes the macroscopic behavior of many micro-particles in Brownian motion, resulting from the random movements and collisions of the particles (see Fick's la ...
s to calculate the probability of fixation of beneficial, deleterious, or neutral
allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chrom ...
s. Combining theoretical population genetics with
molecular evolution Molecular evolution is the process of change in the sequence composition of cellular molecules such as DNA, RNA, and proteins across generations. The field of molecular evolution uses principles of evolutionary biology and population genet ...
data, he also developed the neutral theory of molecular evolution in which
genetic drift Genetic drift, also known as allelic drift or the Wright effect, is the change in the frequency of an existing gene variant (allele) in a population due to random chance. Genetic drift may cause gene variants to disappear completely and there ...
is the main force changing allele frequencies. James F. Crow, himself a renowned population geneticist, considered Kimura to be one of the two greatest evolutionary geneticists, along with
Gustave Malécot Gustave Malécot (28 December 1911 – November 1998) was a French mathematician whose work on heredity had a strong influence on population genetics. Biography Malécot grew up in L'Horme, a small village near St. Étienne in the Loir ...
, after the great trio of the
modern synthesis Modern synthesis or modern evolutionary synthesis refers to several perspectives on evolutionary biology, namely: * Modern synthesis (20th century), the term coined by Julian Huxley in 1942 to denote the synthesis between Mendelian genetics and ...
,
Ronald Fisher Sir Ronald Aylmer Fisher (17 February 1890 – 29 July 1962) was a British polymath who was active as a mathematician, statistician, biologist, geneticist, and academic. For his work in statistics, he has been described as "a genius who ...
,
J. B. S. Haldane John Burdon Sanderson Haldane (; 5 November 18921 December 1964), nicknamed "Jack" or "JBS", was a British-Indian scientist who worked in physiology, genetics, evolutionary biology, and mathematics. With innovative use of statistics in biolo ...
, and
Sewall Wright Sewall Green Wright FRS(For) Honorary FRSE (December 21, 1889March 3, 1988) was an American geneticist known for his influential work on evolutionary theory and also for his work on path analysis. He was a founder of population genetics alongsi ...
.


Life and work

Kimura was born in Okazaki,
Aichi Prefecture is a prefecture of Japan located in the Chūbu region of Honshū. Aichi Prefecture has a population of 7,552,873 () and a geographic area of with a population density of . Aichi Prefecture borders Mie Prefecture to the west, Gifu 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 Foodborne illness (also foodborne disease and food poisoning) is any illness resulting from the spoilage of contaminated food by pathogenic bacteria, viruses, or parasites that contaminate food, as well as prions (the agents of mad cow disea ...
). After entering a selective high school in
Nagoya is the largest city in the Chūbu region, the fourth-most populous city and third most populous urban area in Japan, with a population of 2.3million in 2020. Located on the Pacific coast in central Honshu, it is the capital and the most po ...
, 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 Biostatistics (also known as biometry) are the development and application of statistical methods to a wide range of topics in biology. It encompasses the design of biological experiments, the collection and analysis of data from those experimen ...
. Due to
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
, Kimura left high school early to enter Kyoto Imperial University in 1944. On the advice of the prominent geneticist
Hitoshi Kihara was a Japanese geneticist known for his work on the genetics of wheat. Biography Hitoshi Kihara was born on 21 October 1893 in Tokyo, Japan. He graduated from the Faculty of Agriculture, Hokkaido Imperial University and served as a professor a ...
, 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. 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 Sewall Green Wright FRS(For) Honorary FRSE (December 21, 1889March 3, 1988) was an American geneticist known for his influential work on evolutionary theory and also for his work on path analysis. He was a founder of population genetics alongsi ...
's earlier "island model". After meeting visiting American geneticist Duncan McDonald (part of the
Atomic Bomb Casualty Commission The Atomic Bomb Casualty Commission (ABCC) ( Japanese:原爆傷害調査委員会, ''Genbakushōgaichōsaiinkai'') was a commission established in 1946 in accordance with a presidential directive from Harry S. Truman to the National Academy of ...
), Kimura arranged to enter graduate school at Iowa State College in the summer 1953 to study with J. L. Lush. 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 Sewall Green Wright FRS(For) Honorary FRSE (December 21, 1889March 3, 1988) was an American geneticist known for his influential work on evolutionary theory and also for his work on path analysis. He was a founder of population genetics alongsi ...
. 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 John Burdon Sanderson Haldane (; 5 November 18921 December 1964), nicknamed "Jack" or "JBS", was a British-Indian scientist who worked in physiology, genetics, evolutionary biology, and mathematics. With innovative use of statistics in biolo ...
. 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 In statistical mechanics, the Fokker–Planck equation is a partial differential equation that describes the time evolution of the probability density function of the velocity of a particle under the influence of drag forces and random forces, ...
by introducing the
Kolmogorov backward equation In probability theory, Kolmogorov equations, including Kolmogorov forward equations and Kolmogorov backward equations, characterize continuous-time Markov processes. In particular, they describe how the probability that a continuous-time Markov pr ...
to population genetics, allowing the calculation of the probability of an allele to become
fixed Fixed may refer to: * ''Fixed'' (EP), EP by Nine Inch Nails * ''Fixed'', an upcoming 2D adult animated film directed by Genndy Tartakovsky * Fixed (typeface), a collection of monospace bitmap fonts that is distributed with the X Window System * F ...
in a population. 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). Kimura worked on a wide spectrum of theoretical population genetics problems, many of them in collaboration with
Takeo Maruyama Takeo may refer to: * Takéo Province, a province of Cambodia ** Doun Kaev (town), formerly known as Takéo, the capital of Takéo province * Ta Keo, an Angkorian temple in Cambodia * Takeo, Saga, a city in Saga Prefecture, Japan * Takeo (given nam ...
. He introduced the " infinite alleles", " infinite sites", and " stepwise" models of mutation, all of which would be used widely as the field of
molecular evolution Molecular evolution is the process of change in the sequence composition of cellular molecules such as DNA, RNA, and proteins across generations. The field of molecular evolution uses principles of evolutionary biology and population genet ...
grew alongside the number of available
peptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. ...
and
genetic sequence A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides forming alleles within a DNA (using GACT) or RNA (GACU) molecule. By convention, sequences are us ...
s. The stepwise mutation model is a "ladder model" that can be applied to
electrophoresis Electrophoresis, from Ancient Greek ἤλεκτρον (ḗlektron, "amber") and φόρησις (phórēsis, "the act of bearing"), is the motion of dispersed particles relative to a fluid under the influence of a spatially uniform electric fi ...
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 Genetic load is the difference between the fitness of an average genotype in a population and the fitness of some reference genotype, which may be either the best present in a population, or may be the theoretically optimal genotype. The average i ...
in 1961. 1968 marked a turning point in Kimura's career. In that year he introduced the
neutral theory of molecular evolution The neutral theory of molecular evolution holds that most evolutionary changes occur at the molecular level, and most of the variation within and between species are due to random genetic drift of mutant alleles that are selectively neutral. The ...
, the idea that, at the molecular level, the large majority of genetic change is neutral with respect to
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Cha ...
—making
genetic drift Genetic drift, also known as allelic drift or the Wright effect, is the change in the frequency of an existing gene variant (allele) in a population due to random chance. Genetic drift may cause gene variants to disappear completely and there ...
a primary factor in
evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
. The field of
molecular biology Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and phys ...
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 Exaptation and the related term co-option describe a shift in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another. Exaptations are common ...
for use in the quantitative study of neutral evolution". 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. Kimura produced a monograph on the neutral theory in 1983, ''
The Neutral Theory of Molecular Evolution ''The Neutral Theory of Molecular Evolution'' is an influential monograph written in 1983 by Japanese evolutionary biologist Motoo Kimura. While the neutral theory of molecular evolution existed since his article in 1968, Kimura felt the need to ...
'', 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. 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 The Darwin Medal is one of the medals awarded by the Royal Society for "distinction in evolution, biological diversity and developmental, population and organismal biology". In 1885, International Darwin Memorial Fund was transferred to the ...
from the
Royal Society The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...
, and the following year he was made a
Foreign Member of the Royal Society Fellowship of the Royal Society (FRS, ForMemRS and HonFRS) is an award granted by the judges of the Royal Society of London to individuals who have made a "substantial contribution to the improvement of natural knowledge, including mathematic ...
. Kimura suffered from progressive weakening caused by
amyotrophic lateral sclerosis Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or Lou Gehrig's disease, is a neurodegenerative disease that results in the progressive loss of motor neurons that control voluntary muscles. ALS is the most commo ...
later in life. After an accidental fall at his home in Shizuoka, Japan, Kimura struck his head and died on November 13, 1994, of a cerebral hemorrhage. He was married to Hiroko Kimura. They had one child, a son, Akio, and a granddaughter, Hanako. Brenner's Encyclopedia of Genetics, 2nd Edition

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Honors

* 1959 – Genetics Society of Japan Prize * 1965 – Weldon Memorial Prize, Oxford * 1968 – Japan Academy Prize * 1973 – Foreign member of the National Academy of Sciences of the USA * 1976 –
Person of Cultural Merit is an official Japanese recognition and honor which is awarded annually to select people who have made outstanding cultural contributions. This distinction is intended to play a role as a part of a system of support measures for the promotion of ...
* 1976 –
Order of Culture The is a Japanese order, established on February 11, 1937. The order has one class only, and may be awarded to men and women for contributions to Japan's art, literature, science, technology, or anything related to culture in general; recipient ...
* 1982 – Member of the Japan Academy * 1986 – Chevalier de l'Ordre Nationale de Merite * 1986 –
Asahi Prize The , established in 1929, is an award presented by the Japanese newspaper ''Asahi Shimbun'' and Asahi Shimbun Foundation to honor individuals and groups that have made outstanding accomplishments in the fields of arts and academics and have greatl ...
* 1987 – John J. Carty Award of the
National Academy of Sciences The National Academy of Sciences (NAS) is a United States nonprofit, non-governmental organization. NAS is part of the National Academies of Sciences, Engineering, and Medicine, along with the National Academy of Engineering (NAE) and the Nat ...
in evolutionary biology * 1988 –
International Prize for Biology The is an annual award for "outstanding contribution to the advancement of research in fundamental biology." The Prize, although it is not always awarded to a biologist, is one of the most prestigious honours a natural scientist can receive. Ther ...
* 1992 –
Darwin Medal The Darwin Medal is one of the medals awarded by the Royal Society for "distinction in evolution, biological diversity and developmental, population and organismal biology". In 1885, International Darwin Memorial Fund was transferred to the ...
Royal Society
archived record
/ref> * 1993 – Foreign member of
Royal Society The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...


See also

*
History of biology The history of biology traces the study of the living world from ancient to modern times. Although the concept of ''biology'' as a single coherent field arose in the 19th century, the biological sciences emerged from traditions of medicine an ...
* History of evolutionary thought *
History of molecular biology The history of molecular biology begins in the 1930s with the convergence of various, previously distinct biological and physical disciplines: biochemistry, genetics, microbiology, virology and physics. With the hope of understanding life at it ...
*
Molecular evolution Molecular evolution is the process of change in the sequence composition of cellular molecules such as DNA, RNA, and proteins across generations. The field of molecular evolution uses principles of evolutionary biology and population genet ...


References

{{DEFAULTSORT:Kimura, Motoo 1924 births 1994 deaths Kyoto University alumni University of Wisconsin–Madison alumni People from Okazaki, Aichi Population geneticists Evolutionary biologists Theoretical biologists Japanese scientists Japanese biologists Japanese molecular biologists Japanese geneticists Foreign Members of the Royal Society Foreign associates of the National Academy of Sciences Recipients of the Order of Culture People with motor neuron disease 20th-century biologists Neutral theory