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biogenetic law n.
The theory that the stages in an organism's embryonic development and differentiation correspond to the stages of evolutionary development characteristic of the species. Also called Haeckel's law, law of recapitulation, recapitulation theory.
postulation, by Ernst Haeckel in 1866, that ontogeny recapitulates phylogeny-i.e., the development of the animal embryo and young traces the evolutionary development of the species. The theory was influential and much-popularized earlier but has been of little significance in elucidating either evolution or embryonic growth.