Skip to main content

Masatoshi Nei, Kyoto Prize-winning evolutionary geneticist, dies at 92

Penn State Evan Pugh University Professor Emeritus was champion of the neutral theory of molecular evolution, and inventor of 'Nei’s distance' measure
23 May 2023

Masatoshi Nei, Evan Pugh University Professor Emeritus at Penn State, a pioneering evolutionary geneticist and a laureate of the prestigious Kyoto Prize, has died at age 92. His extraordinary life was marked by transformative contributions to evolutionary genetics and biology.

Nei joined the Penn State faculty in 1990 as distinguished professor of biology and founding director of the Institute of Molecular Evolutionary Genetics, and he was named Evan Pugh University Professor of Biology in 1994. Prior to his retirement from the University in 2015, he was one of Penn State's most prominent faculty members in the biology department, where with his wife, Nokuno Nei, he endowed the Masatoshi Nei Innovation Prize in Biology.

Nei’s legacy has shaped our world's understanding of evolution at the molecular level. He passionately advocated for the neutral theory of molecular evolution, which holds that most evolutionary changes and the genetic variation within and between species are caused not by natural selection but by random genetic drift. One of a select few to have a statistic named for him, he invented the influential “Nei’s distance,” a cornerstone of population genetic analyses. He also stewarded the development of neighbor-joining, a method for creating phylogenetic trees, and of molecular evolutionary genetics analysis (MEGA) software.

“We are saddened by the news of Professor Nei’s passing and are forever grateful for his research legacy and impact on our college, including through his generous support,” said Tracy Langkilde, Verne M. Willaman Dean of the Penn State Eberly College of Science. “His establishment of the eponymous prize in biological sciences, which recognizes our preeminent faculty for their scientific leadership and innovation, stands as a testament to his forward thinking and impact on the field.”

A prolific writer, Nei authored seminal works including “Molecular Population Genetics and Evolution” (1975), “Molecular Evolutionary Genetics” (1987), “Molecular Evolution and Phylogenetics” (2000) and “Mutation-Driven Evolution” (2013). In 1983, he co-founded the prestigious journal Molecular Biology and Evolution, the leading journal in the field, of which he was also co-editor. He penned his memoir, “My Life as a Molecular Evolutionist,” in 2021.

“Professor Masatoshi Nei was an exceptional scientist, the director of the Institute for Molecular Evolutionary Genetics, and a valued colleague in the biology department at Penn State,” said Beth McGraw, professor and department head of biology in the Eberly College of Science. “His body of work in the field of molecular evolution was simply paradigm shifting. His impact will continue to live on through the methods he developed and his numerous mentees, who are now the world's leaders in evolutionary genomics.”

A testament to his achievements, Nei was the recipient of numerous accolades, including the Kyoto Prize in Basic Sciences (2013), International Prize for Biology (2002) and Thomas Hunt Morgan Medal (2006). He was elected to the U.S. National Academy of Sciences (1997) and the American Academy of Arts and Sciences (1990). In 2017, Nei won the prestigious Philadelphia-based John Scott Award for contributing to the “comfort, welfare and happiness” of humankind. Past winners include Marie Curie, Thomas Edison, Jonas Salk and Nikola Tesla.

Nei received many other awards throughout his career. In 2003, he was awarded the Barbara Bowman Award from the Texas Genetics Society. He was awarded an honorary doctoral degree from Miyazaki University in Japan in 2002. In 2000, he received a certificate of award from the Institute for Scientific Information as a highly cited researcher, and that same year the Society for Molecular Biology and Evolution established the Masatoshi Nei Annual Lecture in his honor. Nei also received the Kihara Prize of the Genetics Society of Japan in 1990 and the Japan Society of Human Genetics Award in 1977.

Nei worked with many collaborators in his development of various statistical methods to determine the molecular mechanisms of biological diversity and of evolution. He constructed a mathematical theory for studying the evolutionary relationships of different species using molecular data. A statistic named for him, Nei's standard genetic distance, is a cornerstone of population genetic analyses. This measure makes it possible to estimate the origins of populations and the times of their divergence from common ancestors. Nei applied this technique to human populations and obtained the first evidence pointing to the African origins of modern humans. This paper on genetic distance has been listed among the 1,000 most cited papers in all scientific fields.

An even more influential paper is about the proposal of the "neighbor-joining" method of constructing phylogenetic trees, and is one of the most highly cited papers in the entire field of biology. He also developed several new evolutionary concepts, such as "birth-and-death evolution of multigene families" and "mutation-driven evolution." In addition to his publications, Nei and his group wrote and distributed software packages, including MEGA for molecular evolutionary genetics analysis, which is the most widely used software for phylogenetic analysis at present.

“Masatoshi’s passing is a profound loss to the global scientific community. He leaves behind a devoted wife, two children, their families, and countless colleagues and students, who benefited from his warmth, collaboration, wisdom and mentorship,” said Sudhir Kumar, who earned his doctorate and did his postdoctoral research with Nei at Penn State and now is Laura H. Carnell Professor of Biology at Temple University and director of its Institute for Genomics and Evolutionary Medicine. “As we mourn his loss, we also celebrate the life of a scientist who forever transformed our understanding of the world at a molecular level. His work, legacy and memory will undoubtedly continue to inspire and influence future generations.”

Nei was the author or co-author of many influential papers and six books, and he served on numerous editorial and review boards in the United States, Japan, and Italy. Nei’s work was recognized with his election as an honorary member of the Genetics Society of Japan in 1989 and of the Japan Society of Human Genetics in 1996 as well as his election as a member of the U.S. National Academy of Sciences in 1997, an honorary member of the Japan Society for Histocompatibility and Immunogenetics in 2000, and an honorary member of the Japan Society of Animal Genetics and Breeding in 2001.

Nei earned a bachelor's degree in genetics at the Miyazaki University of Japan in 1953, and he earned a master's degree and a doctoral degree in quantitative genetics at Kyoto University in Japan in 1955 and 1959, respectively. He was an assistant professor at Kyoto University in Japan from 1958 to 1962, a geneticist at the National Institute of Radiological Sciences in Japan from 1962 to 1969, and head of the Population Genetics Laboratory at the National Institute of Radiological Sciences in Japan from 1965 to 1969. He moved to the U.S. in 1969, where he held the positions of associate professor and professor at Brown University from 1969 to 1972; professor of population genetics at the University of Texas at Houston from 1972 to 1990; and acting director of the Center for Demographic and Population Genetics at the University of Texas at Houston from 1979 to 1980 and again from 1986 to 1987. He also was a visiting professor of biology at Tokyo Institute of Technology in Japan for three months in 2001.