Kimura's 1983 paper

Kimura’s 1983 paper introduces the Neutral Theory of Molecular Evolution, proposing that most genetic mutations are neutral—neither beneficial nor harmful—and their changes in frequency are primarily due to random chance, called genetic drift. This contrasts with the idea that natural selection drives all evolution. Kimura emphasizes that, over time, these neutral mutations significantly influence genetic variation within and between species. The theory helps explain why molecular differences accumulate gradually and unpredictably, highlighting the role of randomness in evolution rather than solely adaptive changes.