Born: 7 September 1933, Japan
Died: NA
Country most active: Japan
Also known as: 太田 朋子, Ōta Tomoko, Tomoko Harada 原田 朋子
The following bio was written by Emma Rosen, author of On This Day She Made History: 366 Days With Women Who Shaped the World and This Day In Human Ingenuity & Discovery: 366 Days of Scientific Milestones with Women in the Spotlight, and has been republished with permission.
Tomoko Ohta is a renowned scientist and Professor Emeritus at the National Institute of Genetics. She specializes in population genetics and molecular evolution and is famous for her work on the nearly neutral theory of evolution.
In the early 1960s, genetic theories about natural selection assumed that inherited mutations were either harmful and eliminated or beneficial and passed down. This implied high similarity among individuals in a population. However, in 1966, Richard Lewontin and John Lee Hubby discovered unexpected genetic variation among individuals.
Motoo Kimura proposed the neutral theory of evolution, suggesting that some gene variants were neither advantageous nor harmful and thus unaffected by natural selection.
Working alongside Kimura on the neutral theory, Ohta believed the division into good, neutral, and harmful mutations was too simplistic. She introduced the slightly deleterious model of molecular evolution and later the broader nearly neutral theory. Ohta’s theory challenged Kimura’s views but fostered a friendly debate between them.
Ohta’s theory introduced a new class of origin-fixation models. It revealed that while most mutations affecting encoded proteins were harmful, those “nearly neutral” could persist in the population. Ohta also explored the role of chance and population size, showing that smaller populations allowed slightly deleterious mutations to spread more easily due to genetic drift.
In 1974, Kimura and Ohta proposed five general principles influencing molecular evolution. Initially, Ohta faced challenges in gaining acceptance for her Nearly Neutral theory. However, accumulating evidence in protein evolution throughout the 1990s and beyond increasingly supported her groundbreaking ideas, solidifying the importance of the nearly neutral theory of evolution.