theory, stated as the biogenetic law by E. H. Haeckel
, that the embryological development of the individual repeats the stages in the evolutionary development of the species. For example, the beginnings of gill clefts appear in both humans and fish, but while they are elaborated and eventually function in the fish, in humans, except for the modified gill cleft that becomes the Eustachian tube, they disappear as the embryo develops. Though drastically modified and qualified since its proposal, the historical significance of this theory—"ontogenesis recapitulates phylogenesis"—is that with its appearance it lent support to the theory of evolution
by seeming to corroborate it.
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