Motoo Kimura
Encyclopedia
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 geneticist
s. He is remembered in genetics for his innovative use of diffusion equations to calculate the probability of fixation of beneficial, deleterious, or neutral allele
s. 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 F. Crow
, himself a renowned population geneticist, considers Kimura to be one of the two greatest evolutionary geneticists, along with Gustave Malécot
, after the great trio of the modern synthesis
(Haldane, Wright
, Fisher
).
, 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. 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 immigration than Sewall Wright
's earlier "island model". After meeting visiting American geneticist Duncan McDonald (part of Atomic Bomb Casualty Commission
), Kimura arranged to enter graduate school at Iowa State College in 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 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. 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 a gene 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 allele" and "infinite site" models for the study of genetic drift
, both of which would be used widely as the field of molecular evolution
grew alongside the number of available peptide
and genetic sequences. He also created the "ladder model" that could 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 (though with plenty of divergence from this pattern on both sides, especially among those who studied the theory seriously).
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. In 1973, his colleague Tomoko Ohta
developed a more general version of the theory, the "nearly neutral theory
", that could account for high volumes of slightly deleterious mutations. 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
, and the following year he was made a Foreign Member of the Royal Society. He was married to Hiroko Kimura. They have one child, a son, Akio, and have a granddaughter, Hanako.
Neutral theory of molecular evolution
The neutral theory of molecular evolution states that the vast majority of evolutionary changes at the molecular level are caused by random drift of selectively neutral mutants . The theory was introduced by Motoo Kimura in the late 1960s and early 1970s...
in 1968. He became one of the most influential theoretical population geneticist
Population genetics
Population genetics is the study of allele frequency distribution and change under the influence of the four main evolutionary processes: natural selection, genetic drift, mutation and gene flow. It also takes into account the factors of recombination, population subdivision and population...
s. He is remembered in genetics for his innovative use of diffusion equations to calculate the probability of fixation of beneficial, deleterious, or neutral allele
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
s. Combining theoretical population genetics
Population genetics
Population genetics is the study of allele frequency distribution and change under the influence of the four main evolutionary processes: natural selection, genetic drift, mutation and gene flow. It also takes into account the factors of recombination, population subdivision and population...
with molecular evolution
Molecular evolution
Molecular evolution is in part a process of evolution at the scale of DNA, RNA, and proteins. Molecular evolution emerged as a scientific field in the 1960s as researchers from molecular biology, evolutionary biology and population genetics sought to understand recent discoveries on the structure...
data, he also developed the neutral theory of molecular evolution
Neutral theory of molecular evolution
The neutral theory of molecular evolution states that the vast majority of evolutionary changes at the molecular level are caused by random drift of selectively neutral mutants . The theory was introduced by Motoo Kimura in the late 1960s and early 1970s...
in which genetic drift
Genetic drift
Genetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...
is the main force changing allele
Allele
An allele is one of two or more forms of a gene or a genetic locus . "Allel" is an abbreviation of allelomorph. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation...
frequencies
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
. James F. Crow
James F. Crow
James F. Crow is Professor Emeritus of Genetics at the University of Wisconsin–Madison.Some of his most significant peer-reviewed contributions were coauthored with Motoo Kimura. His major contribution to the field, however, is arguably his teaching...
, himself a renowned population geneticist, considers Kimura to be one of the two greatest evolutionary geneticists, along with Gustave Malécot
Gustave Malécot
Gustave Malécot was a French mathematician whose work on heredity had a strong influence on population genetics.- Biography :...
, after the great trio of the modern synthesis
Modern evolutionary synthesis
The modern evolutionary synthesis is a union of ideas from several biological specialties which provides a widely accepted account of evolution...
(Haldane, Wright
Sewall Wright
Sewall Green Wright was an American geneticist known for his influential work on evolutionary theory and also for his work on path analysis. With R. A. Fisher and J.B.S. Haldane, he was a founder of theoretical population genetics. He is the discoverer of the inbreeding coefficient and of...
, Fisher
Ronald Fisher
Sir Ronald Aylmer Fisher FRS was an English statistician, evolutionary biologist, eugenicist and geneticist. Among other things, Fisher is well known for his contributions to statistics by creating Fisher's exact test and Fisher's equation...
).
Life and work
Kimura was born in OkazakiOkazaki, Aichi
is a city located in Aichi Prefecture, Japan. As of August 2011, the city had an estimated population of 373,339 and a population density of 964 persons per km². The total area was 387.24 km².-Geography:...
, Aichi Prefecture
Aichi Prefecture
is a prefecture of Japan located in the Chūbu region. The region of Aichi is also known as the Tōkai region. The capital is Nagoya. It is the focus of the Chūkyō Metropolitan Area.- History :...
. 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
Liliaceae
The Liliaceae, or the lily family, is a family of monocotyledons in the order Liliales. Plants in this family have linear leaves, mostly with parallel veins but with several having net venation , and flower arranged in threes. Several have bulbs, while others have rhizomes...
. With Kumazawa, he also discovered how to connect his interests in botany and mathematics: biometry.
Due to World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, 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
Mishima, Shizuoka
is a city located in eastern Shizuoka Prefecture, Japan. As of 2009, the city has an estimated population of 112,078 and a population density of 1,800 persons per km². The total area is 62.13 km²...
. 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 immigration than Sewall Wright
Sewall Wright
Sewall Green Wright was an American geneticist known for his influential work on evolutionary theory and also for his work on path analysis. With R. A. Fisher and J.B.S. Haldane, he was a founder of theoretical population genetics. He is the discoverer of the inbreeding coefficient and of...
's earlier "island model". After meeting visiting American geneticist Duncan McDonald (part of Atomic Bomb Casualty Commission
Atomic Bomb Casualty Commission
The Atomic Bomb Casualty Commission was a commission established in 1946 in accordance with a presidential directive from Harry S. Truman to the National Academy of Sciences-National Research Council to conduct investigations of the late effects of radiation among the atomic-bomb survivors in...
), Kimura arranged to enter graduate school at Iowa State College in 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
James F. Crow
James F. Crow is Professor Emeritus of Genetics at the University of Wisconsin–Madison.Some of his most significant peer-reviewed contributions were coauthored with Motoo Kimura. His major contribution to the field, however, is arguably his teaching...
and join a strong intellectual community of like-minded geneticists, including Newton Morton and most significantly, Sewall Wright
Sewall Wright
Sewall Green Wright was an American geneticist known for his influential work on evolutionary theory and also for his work on path analysis. With R. A. Fisher and J.B.S. Haldane, he was a founder of theoretical population genetics. He is the discoverer of the inbreeding coefficient and of...
. 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
Fokker-Planck equation
The Fokker–Planck equation describes the time evolution of the probability density function of the velocity of a particle, and can be generalized to other observables as well.It is named after Adriaan Fokkerand Max Planck...
by introducing the Kolmogorov backward equation
Kolmogorov backward equation
The Kolmogorov backward equation and its adjoint sometimes known as the Kolmogorov forward equation are partial differential equations that arise in the theory of continuous-time continuous-state Markov processes. Both were published by Andrey Kolmogorov in 1931...
to population genetics, allowing the calculation of the probability of a gene to become fixed
Fixation (population genetics)
In population genetics, fixation is the change in a gene pool from a situation where there exist at least two variants of a particular gene to a situation where only one of the alleles remains...
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 allele" and "infinite site" models for the study of genetic drift
Genetic drift
Genetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...
, both of which would be used widely as the field of molecular evolution
Molecular evolution
Molecular evolution is in part a process of evolution at the scale of DNA, RNA, and proteins. Molecular evolution emerged as a scientific field in the 1960s as researchers from molecular biology, evolutionary biology and population genetics sought to understand recent discoveries on the structure...
grew alongside the number of available peptide
Peptide sequence
Peptide sequence or amino acid sequence is the order in which amino acid residues, connected by peptide bonds, lie in the chain in peptides and proteins. The sequence is generally reported from the N-terminal end containing free amino group to the C-terminal end containing free carboxyl group...
and genetic sequences. He also created the "ladder model" that could be applied to electrophoresis
Electrophoresis
Electrophoresis, also called cataphoresis, is the motion of dispersed particles relative to a fluid under the influence of a spatially uniform electric field. This electrokinetic phenomenon was observed for the first time in 1807 by Reuss , who noticed that the application of a constant electric...
studies where homologous
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
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
In population genetics, genetic load or genetic burden is a measure of the cost of lost alleles due to selection or mutation...
in 1961.
1968 marked a turning point in Kimura's career. In that year he introduced the neutral theory of molecular evolution
Neutral theory of molecular evolution
The neutral theory of molecular evolution states that the vast majority of evolutionary changes at the molecular level are caused by random drift of selectively neutral mutants . The theory was introduced by Motoo Kimura in the late 1960s and early 1970s...
, the idea that, at the molecular level, the large majority of genetic change is neutral with respect to natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
—making genetic drift
Genetic drift
Genetic drift or allelic drift is the change in the frequency of a gene variant in a population due to random sampling.The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces...
a primary factor in evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
. The field of molecular biology
Molecular biology
Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...
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 (though with plenty of divergence from this pattern on both sides, especially among those who studied the theory seriously).
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
Preadaptation
In evolutionary biology, preadaptation describes a situation where a species evolves to use a preexisting structure or trait inherited from an ancestor for a potentially unrelated function...
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. In 1973, his colleague Tomoko Ohta
Tomoko Ohta
is a Japanese scientist working on molecular evolution. In 1956, she graduated from the University of Tokyo. After working on the neutral theory of evolution with her mentor, Motoo Kimura, she became convinced of the importance of the mutations that were nearly neutral. She developed the slightly...
developed a more general version of the theory, the "nearly neutral theory
Nearly neutral theory of molecular evolution
The nearly neutral theory of molecular evolution is a modification of the neutral theory of molecular evolution that accounts for slightly advantageous or deleterious mutations at the molecular level...
", that could account for high volumes of slightly deleterious mutations. Kimura produced a monograph on the neutral theory in 1983, The neutral theory of molecular evolution
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 write a monograph with up-to-date information and...
, 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
Darwin Medal
The Darwin Medal is awarded by the Royal Society every alternate year for "work of acknowledged distinction in the broad area of biology in which Charles Darwin worked, notably in evolution, population biology, organismal biology and biological diversity". First awarded in 1890, it was created in...
from the Royal Society
Royal Society
The Royal Society of London for Improving Natural Knowledge, known simply as the Royal Society, is a learned society for science, and is possibly the oldest such society in existence. Founded in November 1660, it was granted a Royal Charter by King Charles II as the "Royal Society of London"...
, and the following year he was made a Foreign Member of the Royal Society. He was married to Hiroko Kimura. They have one child, a son, Akio, and have a granddaughter, Hanako.
Honors
- Genetics Society of Japan Prize, 1959
- Weldon Memorial PrizeWeldon Memorial PrizeThe Weldon Memorial Prize, also known as the Weldon Memorial Prize and Medal, is given yearly by the University of Oxford. The prize is to be awarded...
, Oxford, 1965 - Japan Academy Prize, 1968
- Order of CultureOrder of CultureThe 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 or culture; recipients of the order also receive an annuity for life...
, 1976 - Chevalier de l'Ordre Nationale de Merite, 1986
- Asahi Shimbun Prize, 1987
- John J. Carty Award of the National Academy of SciencesUnited States National Academy of SciencesThe National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...
in evolutionary biology, 1987 - Royal SocietyRoyal SocietyThe Royal Society of London for Improving Natural Knowledge, known simply as the Royal Society, is a learned society for science, and is possibly the oldest such society in existence. Founded in November 1660, it was granted a Royal Charter by King Charles II as the "Royal Society of London"...
, Darwin Medal in 1992; Foreign member, 1993.
See also
- History of biologyHistory of biologyThe 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 and natural history reaching back to ayurveda, ancient Egyptian...
- History of evolutionary thoughtHistory of evolutionary thoughtEvolutionary thought, the conception that species change over time, has roots in antiquity, in the ideas of the ancient Greeks, Romans, and Chinese as well as in medieval Islamic science...
- History of molecular biologyHistory of molecular biologyThe history of molecular biology begins in the 1930s with the convergence of various, previously distinct biological disciplines: biochemistry, genetics, microbiology, and virology...
- Molecular evolutionMolecular evolutionMolecular evolution is in part a process of evolution at the scale of DNA, RNA, and proteins. Molecular evolution emerged as a scientific field in the 1960s as researchers from molecular biology, evolutionary biology and population genetics sought to understand recent discoveries on the structure...