Motoo Kimura
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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 speciali ...
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 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 law ...
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 chro ...
s. Combining theoretical population genetics with
molecular evolution Molecular evolution is the process of change in the sequence composition of cell (biology), cellular molecules such as DNA, RNA, and proteins across generations. The field of molecular evolution uses principles of evolutionary biology and popula ...
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, after the great trio of the modern synthesis,
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, 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 alon ...
.


Life and work

Kimura was born in
Okazaki Okazaki may refer to: *Okazaki (surname) *Okazaki, Aichi, a city in Japan *Okazaki Castle, a castle in Japan *Okazaki fragments Okazaki fragments are short sequences of DNA nucleotides (approximately 150 to 200 base pairs long in eukaryotes) w ...
, 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 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 p ...
, 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 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, 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 alon ...
'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 Jay Laurence Lush (January 3, 1896 – May 22, 1982) was a pioneering animal geneticist who made important contributions to livestock breeding. He is sometimes known as the father of modern scientific animal breeding. Lush received National Med ...
. 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 alon ...
. 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. 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, a ...
by introducing the Kolmogorov backward equation to population genetics, allowing the calculation of the probability of an allele to become fixed 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. 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 cell (biology), cellular molecules such as DNA, RNA, and proteins across generations. The field of molecular evolution uses principles of evolutionary biology and popula ...
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 sequences. 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 f ...
studies where
homologous Homology may refer to: Sciences Biology *Homology (biology), any characteristic of biological organisms that is derived from a common ancestor *Sequence homology, biological homology between DNA, RNA, or protein sequences * Homologous chrom ...
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 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 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'', 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 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, r ...
, and the following year he was made a Foreign Member of the Royal Society. 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 comm ...
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 * 1976 – Order of Culture * 1982 – Member of the Japan Academy * 1986 – Chevalier de l'Ordre Nationale de Merite * 1986 – Asahi Prize * 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 * 1992 – Darwin MedalRoyal 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, r ...


See also

* History of biology *
History of evolutionary thought Evolutionary thought, the recognition that species change over time and the perceived understanding of how such processes work, has roots in antiquity—in the ideas of the ancient Greeks, Romans, Chinese, Church Fathers as well as in medi ...
* History of molecular biology *
Molecular evolution Molecular evolution is the process of change in the sequence composition of cell (biology), cellular molecules such as DNA, RNA, and proteins across generations. The field of molecular evolution uses principles of evolutionary biology and popula ...


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