Ernst Haeckel claimed embryos replay evolution; a marine biologist turned it around
In 1866 Ernst Haeckel proposed that an embryo's growth briefly re-runs its species' evolutionary history, a slogan summed up as ontogeny recapitulates phylogeny. It did not hold up. Walter Garstang flipped the idea: individual development does not repeat evolution, it creates the raw material for it.
Ontogeny, or ontogenesis, is the story of one organism's development, usually from fertilised egg to adult, and it covers psychological growth such as moral development as well as the body. It includes everything from early changes in the egg to growth, reshaping of the body and the appearance of secondary sexual traits after birth or hatching. The word also names the study of a whole lifespan. The contrast is with phylogeny: individuals develop, species evolve.
The term joins Greek words for a being and for origin or mode of production. Its main components are morphogenesis, the shaping of form, along with tissue growth and cell differentiation, and it overlaps so heavily with embryology and developmental biology that the terms are sometimes swapped. It matters in genetics, cell biology, developmental psychology and neuroscience, and anthropologists use it for the way every person physically carries the story of how they were formed.
Haeckel, a German zoologist born in 1834 and an ardent Darwinist, coined the word in the 1860s and set out his biogenetic law in General Morphology of Organisms. He imagined each generation passing through its ancestors' stages and adding something new, with natural selection weeding out obsolete species. Scientists were largely unconvinced, so he kept publishing to win attention. His scheme was not justified, but later embryologists reworked it to show how inherited changes to embryonic development can generate new anatomical structures.
In a landmark 1963 paper, Nikolaas Tinbergen made ontogeny one of biology's four central questions, alongside causation, survival value and evolution, the three proposed by Julian Huxley. He separated changes in an animal's behavioural machinery from mere changes in its behaviour, and warned that labelling a trait innate is reached only by ruling out environmental influence, which is hard to do, making the word often misleading.
Source: Ontogeny
