Masatoshi Nei (????, Nei Masatoshi) (born January 2, 1931) is a Japanese-born American evolutionary biologist currently affiliated with the Department of Biology at Temple University as a Carnell Professor.
He was, until recently, Evan Pugh Professor of Biology at Pennsylvania State University and Director of the Institute of Molecular Evolutionary Genetics; he was there from 1990 to 2015.
Nei was born in 1931 in Miyazaki Prefecture, on Kyushu Island, Japan.
He was associate professor and professor of biology at Brown University from 1969 to 1972 and professor of population genetics at the Center for Demographic and Population Genetics, University of Texas at Houston, from 1972 to 1990.
Acting alone or working with his students, he has continuously developed statistical theories of molecular evolution taking into account discoveries in molecular biology.
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 in 1983 and the Society for Molecular Biology and Evolution in 1993.