定向演化，也成为直生论，是有关生物演化的学说，其基本观点是生物演化按照一定步骤依生物自身能力而向一定方向进行，与外部环境无关。这种观点否认了自然选择的可能。

Orthogenesis also known as orthogenetic evolution is an obsolete biological hypothesis that organisms have an innate tendency to evolve in a unilinear fashion due to some internal mechanism or "driving force".

American paleontologist George Gaylord Simpson (1953) in an attack on orthogenesis described it as "the mysterious inner force". Classic proponents of orthogenesis rejected the theory of natural selection as the organizing mechanism in evolution for a rectilinear model of directed evolution. The term orthogenesis was popularized by Theodor Eimer.