1. the hypothesis that the stages of embryological development of an organism mirror the morphological stages of evolutionary development characteristic of the species; that is, ontogeny recapitulates phylogeny. The theory was abandoned early in the 20th century when embryology showed no consistent correspondence between ontogeny and phylogeny. [proposed by German biologist Ernst H. Haeckel (1834–1919)]

2. the extension of the principle of recapitulation to a child’s mental and behavioral development. [proposed by G. Stanley Hall]