The brainchild of Ernst Haeckel (1834-1919). The theory held that an ontogenetic sequence is a recapitulation in proper order of the corresponding sequence in phylogeny, with the absolute time from conception to maturation remaining the same from ancestors to descendants. In other words, organisms repeat the adult stages of their ancestors during their own ontogeny (metaphorically, they ‘climb up their own family tree’). The theory has been summarized with the catch phrase “ontogeny repeats phylogeny”. The theory eventually lost its credence when it was shown to be incompatible with Mendelian genetics.
See Mendelian genetics, Modern synthesis, Neo-Darwinism, Ontogeny. Phylogeny