生源说（英语：Biogenesis，又称为生源论）是主张生物体只能来源于先存的另一个生命的理论，例如蜘蛛生蛋，后者又发育成蜘蛛。这种理论也指认为生物化学过程只能发生在生物体内。

• 生命起源

Biogenesis is the production of new living organisms or organelles. The law of biogenesis, attributed to Louis Pasteur, is the observation that living things come only from other living things, by reproduction (e.g. a spider lays eggs, which develop into spiders). That is, life does not arise from non-living material, which was the position held by spontaneous generation. This is summarized in the phrase Omne vivum ex vivo, Latin for "all life [is] from life." A related statement is Omnis cellula e cellula, "all cells [are] from cells;" this observation is one of the central statements of cell theory.