Neutral Theory of molecular evolution by Motoo Kimura

In 1968, Motoo Kimura (木村 資生) from the National Institute of Genetics announced the Neutral Theory of molecular evolution. Because it was in conflict with Darwin’s theory of evolution by natural selection, Kimura received much criticism at that time and caused a global dispute.

Kimura was born in Okazaki, Aichi Prefecture in 1924. He studied botany in Kyoto University’s science department and, after studying in the U.S., entered the National Institute of Genetics and was engaged in genetic research.

It was believed that the evolution of genes at the molecular level was by natural selection, as told by Darwin’s theory of evolution. That is, variation caused by mutation would allow species to continue surviving, while those that did not adapt by changing would not survive. However, when Kimura investigated the variation of protein amino acid sequence caused by natural selection, he came to the conclusion that there was no link with natural selection. Thus, he introduced the neutral theory of molecular evolution in 1968. In his opinion, the evolution of a gene is not only based on natural selection, but also happens by a neutral mutation that spreads by chance, irregardless of whether it is advantageous or not.

Since this theory disputed contents of Darwin’s theory of evolution, which at the time was hugely accepted, it generated disagreement and received criticism from many scholars around the world.

However, after the base sequence of DNA was investigated, it revealed that genetic variation happens for particular reasons/functions, but there were also mutations with no identifiable purposes. If Darwin’s theory is correct, variation arises to perform functions. But due to the fact that this was not always the case, Kimura’s neutral theory was accepted as an established theory.

In 1992, Kimura was awarded the Darwin Medal from The Royal Society in Darwin’s birth country, Britain, where he was exposed to criticism at the beginning. It was the first time it was awarded to a Japanese person, and is still the only. The Darwin Medal is a highly-regarded prize, which The Royal Society awards to a biologist who attains outstanding achievements, and is given only once every two years. It is equal to the Nobel Prize. Obtaining such success in Darwin’s mother country speaks of the greatness in Kimura’s achievements.