Which evolutionary theory did Motoo Kimura propose in 1968 to explain many molecular changes as selectively neutral?

Motoo Kimura proposed the neutral theory of molecular evolution in 1968 to explain many molecular changes as selectively neutral.

Kimura argued that a large proportion of changes at the DNA and protein level do not significantly affect an organism’s survival or reproduction. Instead, these neutral mutations can spread or disappear mainly through genetic drift. His proposal was based on emerging molecular data showing that proteins could accumulate substitutions at roughly regular rates.

The theory did not deny natural selection. Kimura explicitly distinguished neutral changes from harmful mutations, which selection tends to remove, and advantageous mutations, which selection can favor. The claim was about the relative importance of neutral evolution at the molecular level.

The neutral theory helped establish molecular evolution as a quantitative field and encouraged researchers to compare DNA and protein sequences. Later versions, including nearly neutral theory, recognized that some mutations have effects too small for selection to dominate over drift, especially in populations of different sizes.