演化中性理论全称为分子演化的中性理论，简称为中性理论。是日本遗传学家木村资生在1968年早期所提出的一种演化理论。

这个理论认为在分子遗传学的层次上，基因的变化大多数是中性突变（neutral mutation），也就是对生物个体既没有好处也没有坏处的突变。由于中性突变并不受自然选择影响，因此中性理论也曾被认为是与查尔斯·达尔文的自然选择论处于竞争状态。另外木村资生提出突然变异产生的蛋白质和原本的蛋白质之间没有适应性的差异时的突然变异则称为中立突然变异的理论。

不过现今的演化生物学家认为，自然选择理论与中性理论是能够并立且互补的。例如木村资生本人便曾在1986年说：「此理论并不否认自然选择对于适应演化上的方向决定」。

The neutral theory of molecular evolution holds that at the molecular level most evolutionary changes and most of the variation within and between species is not caused by natural selection but by genetic drift of mutant alleles that are neutral. A neutral mutation is one that does not affect an organism's ability to survive and reproduce. The neutral theory allows for the possibility that most mutations are deleterious, but holds that because these are rapidly purged by natural selection, they do not make significant contributions to variation within and between species at the molecular level. Mutations that are not deleterious are assumed to be mostly neutral rather than beneficial. In addition to assuming the primacy of neutral mutations, the theory also assumes that the fate of neutral mutations is determined by the sampling processes described by specific models of random genetic drift.