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.

Selected Bibliography:

• M. Kimura, "The theory of the chromosome substitution between two different species," Cytologia (1950), 15: 281-94.
• M. Kimura, "'Stepping-stone model of population," Annual Report of the National Institute of Genetics (1953), 3: 62-63.
• M. Kimura, "Process leading to quasi-fixation of genes in natural populations due to random fluctuation of selection intensities," Genetics (1954), 39:280-295.
• M. Kimura, "Solution of a process of random genetic drift with a continuous model," PNAS (1955), 41: 144-150.
• M. Kimura, "Stochastic Processes and distribution of gene frequencies under natural selection," Cold Spring Harbor Symp. Quant. Biol. (1955), 20: 33-53.
• M. Kimura, "On the probability of fixation of mutant genes in a population," Genetics (1962), 47: 713-19.
• M. Kimura and J.F. Crow, "The measurement of effective population number," Evolution (1963), 17: 279-288.
• M. Kimura and J. F. Crow, "The number of alleles that can be maintained in a finite population," Genetics (1964), 49: 725-38.
• M. Kimura, Diffusion Models in Population Genetics (London: Methun, 1964)
• M. Kimura, "A stochastic model concerning the maintenance of genetic variability in quantitative characters," PNAS (1965), 54: 731-736.
• M. Kimura, "Evolutionary Rate at the Molecular Level," Nature (1968), 217: 624-26.
• M. Kimura, "The number of heterozygous nucleotide sites maintained in a finite population due to steady flux of mutations," Genetics (1969), 61: 893-903.
• M. Kimura and T. Ohta, "The average number of generations until fixation of a mutant gene in a finite population," Genetics (1969), 61: 763-71.
• M. Kimura, "Theoretical foundation of population genetics at the molecular level," Theoretical Population Biology (1971), 2: 174-208.
• T. Ohta and M. Kimura, "A model of mutation appropriate to estimate the number of electrophoretically detectable alleles in a finite population," Genet. Res. (1973), 22: 201-204.
• M. Kimura, The Neutral Theory of Molecular Evolution (Cambridge: Cambridge University Press, 1983).
• M. Kimura, "The neutral theory of molecular evolution: a review of recent evidence," Japanese Journal of Genetics (1991), 66: 367-86.
  

Secondary Sources:

• James Crow, "Motoo Kimura: An Appreciation," in T. Ohta and K. Aoki (eds.), Population Genetics and Molecular Evolution (Tokyo: Japan Scientific Societies Press, 1985) p. 1.
• James Crow, "Twenty-Five Years Ago in Genetics: Motoo Kimura and Molecular Evolution," Genetics (1987), 119:??.
• James Crow, "Twenty-Five Years Ago in Genetics: The Infinite Alleles Model," Genetics (1989), 121: 631-4.
• James Crow, "Motoo Kimura, 1924-1994," Genetics (1995), 140: 1-5.
• James Crow, "Memories of Moto," Theoretical Population Genetics (1996), 49: 122-127.
• Motoo Kimura, "Genes, Populations, and Molecules: A Memoir," in T. Ohta and K. Aoki (eds.) Population Genetics and Molecular Evolution (Tokyo: Japan Scientific Societies Press, 1985), pp. 459-481.
• Motoo Kimura, "Thirty Years of Population Genetics with Dr. Crow," Japanese Journal of Genetics (1988), 63: 1-10.
• Wen-Hsiung Li, "Kimura's Contributions to Molecular Evolution," Theoretical Population Biology (1996), 49: 146-153.
• G. A. Watterson, "Motoo Kimura's Use of Diffusion Theory in Population Genetics," Theoretical Population Biology (1996), 49: 154-188.
• Tomoko Ohta, "Motoo Kimura," Annu. Rev. Genet. (1996), 30: 1-5.