Neutral theory of molecular evolution

The theory that most molecular evolutionary changes arise when selectively neutral mutations become fixed by genetic drift. It distinguishes molecular change from adaptation driven by natural selection.

Genetic drift: Random changes in allele frequencies caused by finite sampling of reproductive individuals. Drift can fix neutral mutations even when they provide no selective advantage.
Motoo Kimura: A Japanese population geneticist who developed the neutral theory of molecular evolution. Kimura formulated the theory and argued that much molecular change is neutral.
Positive selection: Natural selection that increases the frequency of alleles because they improve reproductive success. It drives adaptive substitutions rather than fixation by drift alone.
Synonymous substitution: A DNA substitution that changes a codon without changing the encoded amino acid. Many synonymous changes approximate neutral substitutions, though not all are neutral.
Genetic draft: Changes in allele frequencies caused by linkage to nearby variants under strong selection. Linked selection can distort patterns otherwise attributed to neutral drift.
Mutation–drift equilibrium: The balance between new mutations entering a population and random loss or fixation of alleles. This balance sets neutral variation levels and substitution rates.
Molecular evolution: Evolutionary change in DNA, RNA, and protein sequences across populations and species. The neutral theory arose to explain patterns in molecular sequence variation.
Purifying selection: Natural selection that removes harmful genetic variants from a population. It constrains molecular change where mutations reduce fitness.
Nonsynonymous substitution: A DNA substitution that changes the amino acid encoded by a codon. Its selective effects determine whether drift can fix it or selection removes it.
Background selection: The reduction of linked neutral variation when purifying selection removes deleterious mutations. It shows that neutral sites can be shaped indirectly by selection nearby.

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