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Motoo Kimura

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Caltech, History of Recent Science  & Technology, Profiles-Motoo Kimura, here.

Motoo Kimura (1924-1994) was excited by the living world, especially plants, from an early age. After beginning his biological training in secondary school, he studied botany at Kyoto Imperial University. Upon graduating, he was hired by the renowned geneticist Hitoshi Kihara, a professor in the Universities school of Agriculture. While most other students and workers in the lab spent their idle hours reading up on a particular species, Kimura dove into the works on J.B.S. Haldane, Theodosius Dobzhansky, and Sewall Wright. He taught himself whatever math he needed to know along the way. One of his earliest theoretical accomplishments was the development of the “stepping stone” model of migration, a more realistic version of Wright’s island model.

In 1949, he was hired as a research assistant at the newly established National Institute of Genetics in Mishima, where he was to be employed there for the rest of his life. Four years later, in 1953, Kimura left for United States to study on a Fullbright Fellowship. After nine unsatisfying months at Iowa State, he joined James Crow’s laboratory at the University of Wisconsin, from which he received his Ph.D. in 1956. During this two-year period, he wrote several important, highly mathematical papers on random genetic drift that impressed the few population geneticists who were able to understand them (most notably, Wright). In one paper, he extended Fisher’s theory of natural selection to take into account factors such as dominance, epistasis and fluctuations in the natural environment. After a five year period in Japan, Kimura returned to Crow’s lab at Wisconsin in 1961, where spent the next to years working out such important problems as the fixation probability of a newly occurring mutation and developing the “infinite alleles model” along with Crow.

In 1963, he returned to Japan once again, and set out to develop ways to use the new data pouring in from molecular biology to solve problems of population genetics. Using data on the variation among hemoglobins and cytochromes-c in a wide range of species, he calculated the evolutionary rates of these proteins. After extrapolating these rates to the entire genome, he concluded that there simply could not be strong enough selection pressures to drive such rapid evolution. He therefore decided that most evolution at the molecular level was the result of random processes like mutation and drift. Kimura spent the rest of his life advancing this idea, which came to be known as the “neutral theory of molecular evolution.”

While Kimura did a great deal of important theoretical and experimental work in the 1970s and 1980s (much of it in collaboration with Tomoko Ohta), he is most remembered for his tireless and dogmatic championing of the neutral theory. Some have argued that proving his many detractors wrong became an obsession. Nevertheless, he still found time to make profound contributions to the field of population genetics. Not only was he able to work out the time it takes for a neutral allele to become fixed in a population (4Ne), he also calculated the number of heterozygous nucleotide sites in a finite population in which new mutations are constantly occurring.

Throughout his career, Kimura authored several hundred papers. He also wrote or co-wrote 6 books, including An Introduction to Population Genetics Theory (1970; with James Crow) and The Neutral Theory of Molecular Evolution (1983). His most widely cited papers are collected in the 1994 volume Population Genetics, Molecular Evolution, and the Neutral Theory: Selected Papers. He received innumerable awards during his long career, including: The Genetics Society of Japan Prize (1959); The Weldon Memorial Prize (1965); The Japanese Order of Culture (Emperor’s Prize [1976]), the Chevalier de L’Ordre National du Merite (1986), and the Darwin Medal (Royal Society [1992]). He was elected Foreign Member of the National Academy of Sciences (USA) in 1973, and of the Royal Society in 1993. He died on his 70th birthday, November 13, 1994, after a fall caused by Amyotrophic Lateral Sclerosis.

 

 

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