Recapitulation theory

Ontogeny recapitulates phylogeny, also called the biogenetic law or the theory of recapitulation, is a hypothesis in biology first espoused in 1866 by the German zoologist Ernst Haeckel, a contemporary of Charles Darwin, which has been discredited in its absolute form, although recognised as being partly accurate. In biology, ontogeny is the embryonal development process of a certain species, and phylogeny a species' evolutionary history. Observers have noted various connections between phylogeny and ontogeny, explained them with evolutionary theory and taken them as supporting evidence for that theory.

Haeckel's theory

Ontogeny is the development of the embryos of a given species; phylogeny is the evolutionary history of a species. The theory claims that the development of the embryo of every species repeats the evolutionary development of that species fully. Or otherwise put: each successive stage in the development of an individual represents one of the adult forms that appeared in its evolutionary history. Haeckel formulated his theory as such: "Ontogeny recapitulates phylogeny". This notion later became simply known as recapitulation.

Related Topics:
Ontogeny - Embryos - Species - Phylogeny - Evolutionary

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Fraudulent diagrams

Haeckel produced several embryo drawings which overemphasized similarities between embryos of related species and found their way into many biology textbooks. Modern embryologists such as Richardson (1997) called it "faking".

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For example, the human embryo with gill slits in the neck was believed by Haeckel to not only signify a fishlike ancestor, but it represented a total fishlike stage in development. Gill slits are not the same as gills and are not functional. Gill slits are the invaginations between the gill pouches or pharyngeal pouches, and they open the pharynx to the outside. Gill pouches appear in all tetrapod animal embryos. In mammals, the first gill bar (in the first gill pouch) develops into the lower jaw (Meckel's cartilage), the malleus and the stapes. In a later stage, all gill slits close, with only the ear opening remaining open. For a technical discussion on the topic, see http://www.palaeos.com/Vertebrates/Bones/Gill_Arches/Meckelian.html.

Related Topics:
Gill slit - Gill - Invagination - Gill pouch - Pharynx - Tetrapod - Mammal - Gill bar - Jaw - Meckel's cartilage - Malleus - Stapes

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Modern biology rejects the literal form of Haeckel's theory. While for instance the phylogeny of humans as having evolved from fish through reptiles to mammals is accepted (though 'reptiles' are now known to be a composite group and the ancestors of mammals split off before todays' reptiles evolved), no cleanly defined "fish", "reptile" and "mammal" stages of human embryonal development can be discerned. There is no linearity in the development. For instance in kidney development, at one given time, the anterior region of the kidney is less developed (nephridium) than the posterior region (nephron).

Related Topics:
Humans - Kidney - Nephridium - Nephron

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The fact that the literal form of recapitulation theory is rejected by modern biologists has sometimes been used as an argument against evolution by creationists. The argument is: "Haeckel's theory was presented as supporting evidence for evolution, Haeckel's theory is wrong, therefore evolution has less support". This argument is not only an oversimplification but misleading because modern biology does recognize numerous connections between ontogeny and phylogeny, explains them using evolutionary theory without recourse to Haeckel's specific views, and considers them as supporting evidence for that theory.

Related Topics:
Evolution - Creationists - Ontogeny - Phylogeny

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Historical impact

Although Haeckel's specific form of recapitulation theory is now discredited among biologists, it did have a strong impact in social and educational theories of the late 19th century. The maturationist theory of G. Stanley Hall was based on the premise that growing children would recapitulate evolutionary stages of development as they grew up and that there was a one to one correspondence between childhood stages and evolutionary history, and that it was counterproductive to push a child ahead of its development stage. The whole notion fitted nicely in other social darwinist concepts, such as the idea that "primitive" societies needed guidance by more advanced societies, i.e. Europe and North America, which were the pinnacle of evolution. An early form of the law was devised by the 19th-century Estonian zoologist Karl Ernst von Baer, who observed that embryos resemble the embryos, but not the adults, of other species.

Related Topics:
19th century - G. Stanley Hall - Social darwinist - Zoologist - Karl Ernst von Baer

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