Q.What is meant by 'ontogeny repeats phylogeny'?

The phrase summarises the recapitulation theory proposed by Ernst Haeckel, which links embryonic development to evolutionary history.

Meaning of the terms

• Ontogeny = the developmental history of an individual organism from fertilisation (zygote) through embryonic stages to the adult form.
• Phylogeny = the evolutionary history of the species/lineage that the organism belongs to.

The recapitulation theory (biogenetic law)

Proposed by the German biologist Ernst Haeckel, the statement "ontogeny repeats phylogeny" proposes that, during its own embryonic development, an organism passes through a series of stages that resemble (in a compressed and modified form) the adult stages of its evolutionary ancestors. For example, early vertebrate embryos (fish, amphibians, birds, mammals, including humans) show striking similarities such as pharyngeal (gill) slits and a tail at certain stages, taken as evidence that all vertebrates share a common ancestry and that developmental stages echo evolutionary lineage.

Evidence and limitation

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