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was a Japanese-born American evolutionary biologist.


Professional life

Masatoshi Nei was born in 1931 in Miyazaki Prefecture, on
Kyūshū is the third-largest island of Japan's four main islands and the most southerly of the four largest islands (i.e. excluding Okinawa and the other Ryukyu (''Nansei'') Islands). In the past, it has been known as , and . The historical regio ...
Island, Japan. He received a Bachelor of Science degree from the University of Miyazaki in 1953, and published his first article, on the mathematics of plant breeding, that same year. In 1959, he completed his doctoral degree at Kyoto University on quantitative genetics for crop improvement. For the next decade, Nei worked in Japan, including as a research scientist at the National Institute of Radiological Sciences, before emigrating to the United States in 1969. Nei was associate professor and professor of biology at Brown University from 1969 to 1972 and professor of
population genetics Population genetics is a subfield of genetics that deals with genetic differences within and among populations, and is a part of evolutionary biology. Studies in this branch of biology examine such phenomena as Adaptation (biology), adaptation, s ...
at the Center for Demographic and Population Genetics, University of Texas Health Science Center at Houston (UTHealth), from 1972 to 1990. He was later an Evan Pugh Professor of Biology at
Pennsylvania State University The Pennsylvania State University (Penn State or PSU) is a Public university, public Commonwealth System of Higher Education, state-related Land-grant university, land-grant research university with campuses and facilities throughout Pennsyl ...
and Director of the Institute of Molecular Evolutionary Genetics, working there from 1990 to 2015. From 2015, Nei was affiliated with the Department of Biology at
Temple University Temple University (Temple or TU) is a public university, public Commonwealth System of Higher Education, state-related research university in Philadelphia, Philadelphia, Pennsylvania, United States. It was founded in 1884 by the Baptist ministe ...
as an adjunct Laura H. Carnell Professor. Acting alone or working with his students, he has continuously developed statistical methods for studying
molecular evolution Molecular evolution describes how Heredity, inherited DNA and/or RNA change over evolutionary time, and the consequences of this for proteins and other components of Cell (biology), cells and organisms. Molecular evolution is the basis of phylogen ...
taking into account discoveries in
molecular biology Molecular biology is a branch of biology that seeks to understand the molecule, molecular basis of biological activity in and between Cell (biology), cells, including biomolecule, biomolecular synthesis, modification, mechanisms, and interactio ...
. He has also developed concepts in evolutionary theory and advanced the theory of mutation-driven evolution. Together with Walter Fitch, Nei co-founded the journal ''
Molecular Biology and Evolution ''Molecular Biology and Evolution'' (''MBE'') is a monthly peer-reviewed scientific journal published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. It publishes work in the intersection of molecular bi ...
'' in 1983 and the
Society for Molecular Biology and Evolution The Society for Molecular Biology and Evolution (SMBE) is a scientific and academic organization founded in 1982 to support academic research in the field of molecular evolution. The society hosts an annual meeting, typically in June or July. It al ...
in 1993.


Work in population genetics


Theoretical studies

Nei was the first to show mathematically that, in the presence of
gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...
interaction,
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 Heredity, heritable traits characteristic of a population over generation ...
always tends to enhance the linkage intensity between genetic loci or maintain the same linkage relationship. He then observed that the average recombination value per genome is generally lower in higher organisms than in lower organisms and attributed this observation to his theory of linkage modification. Recent molecular data indicate that many sets of interacting genes such as the Hox genes, immunoglobulin genes, and histone genes have often existed as gene clusters for a long evolutionary time. This observation can also be explained by his theory of linkage modification. He also showed that, unlike R. A. Fisher's argument, deleterious mutations can accumulate rather quickly on the
Y chromosome The Y chromosome is one of two sex chromosomes in therian mammals and other organisms. Along with the X chromosome, it is part of the XY sex-determination system, in which the Y is the sex-determining chromosome because the presence of the ...
or duplicate genes in finite populations. In 1969, considering the rates of amino acid substitution, gene duplication, and gene inactivation, he predicted that higher organisms contain a large number of duplicate genes and nonfunctional genes (now called pseudogenes). This prediction was shown to be correct when many multigene families and pseudogenes were discovered in the 1980s and 1990s. His notable contribution in the early 1970s is the proposal of a new measure of
genetic distance Genetic distance is a measure of the genetics, genetic divergence between species or between population#Genetics, populations within a species, whether the distance measures time from common ancestor or degree of differentiation. Populations with ...
(Nei's distance) between populations and its use for studying evolutionary relationships of populations or closely related species. He later developed another distance measure called DA, which is appropriate for finding the topology of a phylogenetic tree of populations. He also developed statistics of measuring the extent of population differentiation for any types of mating system using the '' G'' ST measure. In 1975, he and collaborators presented a mathematical formulation of population bottleneck effects and clarified the genetic meaning of bottleneck effects. In 1979, he proposed a statistical measure called nucleotide diversity, which is now widely used for measuring the extent of nucleotide polymorphism. He also developed several different models of speciation and concluded that the reproductive isolation between species occurs as a passive process of accumulation of interspecific incompatibility mutations


Protein polymorphism and neutral theory

In the early 1960s and 1970s, there was a great controversy over the mechanism of protein evolution and the maintenance of protein polymorphism. Nei and his collaborators developed various statistical methods for testing 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 ...
using polymorphism data. Their analysis of the allele frequency distribution, the relationship between average heterozygosity and protein divergence between species, etc., showed that a large portion of protein polymorphism can be explained by neutral theory.Nei, M. (1983) Genetic polymorphism and the role of mutation in evolution (M. Nei and P. K. Koehn, eds.) ''Evolution of Genes and Proteins.'' Sinauer Assoc., Sunderland, MA, pp. 165-190.Nei, M. (1987) ''Molecular Evolutionary Genetics.'' Columbia University Press, New York. The only exception was the major histocompatibility complex (MHC) loci, which show an extraordinarily high degree of polymorphism. For these reasons, he accepted the neutral theory of evolution.


Human evolution

Using his genetic distance theory, he and A. K. Roychoudhury showed that the genetic variation between Europeans, Asians, and Africans is only about 11 percent of the total genetic variation of the human population. They then estimated that Europeans and Asians diverged about 55,000 years ago and these two populations diverged from Africans about 115,000 years ago. This conclusion was supported by many later studies using larger numbers of genes and populations, and the estimates appear to be still roughly correct. This finding could be considered an early indication of the out-of-Africa theory of human origins.


Molecular phylogenetics

Around 1980, Nei and his students initiated a study of inference of phylogenetic trees based on distance data. In 1985, they developed a statistical method for testing the accuracy of a phylogenetic tree by examining the statistical significance of interior branch lengths. They then developed the
neighbor joining In bioinformatics, neighbor joining is a bottom-up (agglomerative) clustering method for the creation of phylogenetic trees, created by Naruya Saitou and Masatoshi Nei in 1987. Usually based on DNA or protein sequence data, the algorithm require ...
and minimum-evolution methods of tree inference. They also developed statistical methods for estimating evolutionary times from molecular phylogenies. In collaboration with Sudhir Kumar and Koichiro Tamura, he developed a widely used computer program package for phylogenetic analysis called MEGA.


MHC loci and positive Darwinian selection

Nei's group invented a simple statistical method for detecting positive Darwinian selection by comparing the numbers of synonymous nucleotide substitutions and nonsynonymous nucleotide substitutions. Applying this method, they showed that the exceptionally high degree of sequence polymorphism at MHC loci is caused by overdominant selection. Although various statistical methods for this test have been developed later, their original methods are still widely used.Nei, M. (2013) ''Mutation-Driven Evolution.'' Oxford University Press, Oxford.


New evolutionary concepts

Nei and his students studied the evolutionary patterns of a large number of multigene families and showed that they generally evolve following the model of a
birth–death process The birth–death process (or birth-and-death process) is a special case of continuous-time Markov process where the state transitions are of only two types: "births", which increase the state variable by one and "deaths", which decrease the stat ...
. In some gene families, this process is very fast, caused by random events of gene duplication and gene deletion and generates genomic drift of gene copy number. Nei has long maintained the view that the driving force of evolution is mutation, including any types of DNA changes (nucleotide changes, chromosomal changes, and genome duplication), and that natural selection is primarily a force eliminating less fit genotypes (i.e., theory of mutation-driven evolution). He conducted statistical analyzes of evolution of genes controlling phenotypic characters such as immunity and olfactory reception and obtained evidence supporting this theory.


Personal life

Masatoshi Nei was born in 1931 Japan, and his lifelong interest in biology and genetics may have its roots in his upbringing on a farm, in a family of farmers. After completing his undergraduate and doctorate degrees in Japan, Nei emigrated to the United States in 1969. Nei was married with two children and two grandchildren, and enjoyed listening to classical music and sculpting topiary. In 2014, Nei suffered a stroke and moved to New Jersey after retiring from Pennsylvania State University. Nei died in
Morristown, New Jersey Morristown () is a Town (New Jersey), town in and the county seat of Morris County, New Jersey, Morris County, in the U.S. state of New Jersey.
on May 18, 2023, at the age of 92.


Select awards and honors

* 2017:
John Scott Medal John Scott Award, created in 1816 as the John Scott Legacy Medal and Premium, is presented to men and women whose inventions improved the "comfort, welfare, and happiness of human kind" in a significant way. "...the John Scott Medal Fund, establish ...
* 2013: Kyoto Prize in Basic Sciences * 2006: Thomas Hunt Morgan Medal * 2002: Honorary Doctorate, University of Miyazaki * 2002: International Prize for Biology, Japan Society for the Promotion of Science * 1997: Member,
National Academy of Sciences The National Academy of Sciences (NAS) is a United States nonprofit, NGO, 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 ...


Books

* Nei, M. (2020) ''My Life as a Molecular Evolutionist.'' Blurb, self-published. * Nei, M.(2013) ''Mutation-Driven Evolution.'' Oxford University Press, Oxford. * Nei, M., and S. Kumar (2000) ''Molecular Evolution and Phylogenetics.'' Oxford University Press, Oxford. * National Research Council, (1996) ''The Evaluation of DNA Forensic Evidence''. National Academies Press, Washington D.C. * Roychoudhury, A. K., and M. Nei (1988) ''Human Polymorphic Genes: World Distribution.'' Oxford University Press, Oxford and New York. * Nei, M. (1987) ''Molecular Evolutionary Genetics.'' Columbia University Press, New York. * Nei, M., and R. K. Koehn (eds). (1983) ''Evolution of Genes and Proteins.'' Sinauer Assoc., Sunderland, MA. * Nei, M. (1975) ''Molecular Population Genetics and Evolution.'' North-Holland, Amsterdam and New York.


References


External links

* {{DEFAULTSORT:Nei, Masatoshi 1931 births 2023 deaths Japanese geneticists Japanese molecular biologists American geneticists Statistical geneticists Pennsylvania State University faculty Brown University faculty University of Texas Health Science Center at Houston faculty People from Miyazaki Prefecture Scientists from Miyazaki Prefecture University of Miyazaki alumni Kyoto University alumni Kyoto laureates in Basic Sciences Members of the United States National Academy of Sciences Evolutionary biologists Mutationism Population geneticists Japanese emigrants to the United States American academics of Japanese descent American scientists of Asian descent Temple University faculty Neutral theory