Ontogeny recapitulates phylogeny

The theory of recapitulation, also called the biogenetic law or embryological parallelism—often expressed using Ernst Haeckel's phrase "ontogeny recapitulates phylogeny"—is a largely discredited biological hypothesis that the development of the embryo of an animal, from fertilization to gestation or hatching (ontogeny), goes through stages resembling or representing successive stages in the evolution of the animal's remote ancestors (phylogeny). Since embryos also evolve in different ways, the theory of recapitulation is seen as a historical side-note, rather than as dogma in the field of developmental biology.

With different formulations, including the early Meckel-Serres law, recapitulation theory has been applied and extended to several fields and areas, including the study of language (its origin), religion, biology, cognition and mental activities, anthropology, education theory and developmental psychology. Recapitulation theory is still considered plausible by some researchers in fields such as the study of the origin of language,cognitive development, and behavioral development in animals.

The earliest recorded trace of a recapitulation theory is from the Egyptian Pharaoh Psamtik I (664 – 610 BCE), who used it as a hypothesis on the origin of language. The concept of recapitulation was first formulated outside the field of biology. It was widely held among traditional theories of the origin of language (glottology), being assumed as a premise that children's use of language gives insights on its origin and evolution.

The idea was reprised in 1720 by Giambattista Vico in his influential Scienza Nuova. It was first formulated in biology in the 1790s among the German Natural philosophers, after which, Marcel Danesi states, it soon gained the status of a supposed biogenetic law.

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