Editing Recapitulation theory (section)

===Haeckel===
{{see|Embryo drawing|Icons of Evolution#Haeckel's embryos}}

[[Ernst Haeckel]] (1834–1919) attempted to synthesize the ideas of [[Lamarckism]] and [[Goethe]]'s ''[[Naturphilosophie]]'' with [[Charles Darwin]]'s concepts.  While often seen as rejecting Darwin's theory of branching evolution for a more linear Lamarckian view of progressive evolution, this is not accurate: Haeckel used the Lamarckian picture to describe the ontogenetic and phylogenetic history of individual species, but agreed with Darwin about the branching of all species from one, or a few, original ancestors.<ref>{{cite book | last=Richards | first=Robert J. | title=The tragic sense of life : Ernst Haeckel and the struggle over evolutionary thought | publisher=University of Chicago Press | publication-place=Chicago | date=2008 | isbn=978-0-226-71219-2 | oclc=309071386 | pages=136–142}}</ref> Since early in the twentieth century, Haeckel's "biogenetic law" has been refuted on many fronts.<ref name="Gilbert2006">{{cite web |url=http://11e.devbio.com/ |title=Ernst Haeckel and the Biogenetic Law |access-date=2008-05-03 |author=Scott F Gilbert |year=2006 |work=Developmental Biology, 8th edition |publisher=Sinauer Associates |quote=Eventually, the Biogenetic Law had become scientifically untenable.}}</ref>

Haeckel formulated his theory as "Ontogeny recapitulates phylogeny". The notion later became simply known as the recapitulation theory. [[Ontogeny]] is the growth (size change) and development (structure change) of an individual organism; [[Phylogenetics|phylogeny]] is the [[evolution]]ary history of a species. Haeckel claimed that the development of advanced species passes through stages represented by adult organisms of more primitive species.<ref name="Gilbert2006" /> Otherwise put, each successive stage in the development of an individual represents one of the adult forms that appeared in its evolutionary history.{{cn|date=June 2024}}

For example, Haeckel proposed that the pharyngeal grooves between the [[pharyngeal arch]]es in the neck of the human embryo not only roughly resembled gill slits of fish, but directly represented an adult "fishlike" developmental stage, signifying a fishlike ancestor. Embryonic pharyngeal slits, which form in many animals when the thin branchial plates separating pharyngeal pouches and pharyngeal grooves perforate, open the [[pharynx]] to the outside. Pharyngeal arches appear in all [[tetrapod]] embryos: in [[mammal]]s, the first pharyngeal arch develops into the lower [[jaw]] ([[Meckel's cartilage]]), the [[malleus]] and the [[stapes]].

Haeckel produced several [[embryo drawing]]s that often overemphasized similarities between embryos of related species. Modern biology rejects the literal and universal form of Haeckel's theory, such as its possible application to behavioural ontogeny, i.e. the psychomotor development of young animals and human children.<ref name="Medicus1992">{{cite journal |author=Gerhard Medicus |year=1992 |title=The Inapplicability of the Biogenetic Rule to Behavioral Development |journal=Human Development |volume=35 |issue=1 |pages=1–8 |issn=0018-716X |url=https://www.uibk.ac.at/psychologie/humanethologie/einfuehrung-in-die-humanethologie/dateien/humandevelopment.pdf |access-date=2008-04-30 |quote=The present interdisciplinary article offers cogent reasons why the biogenetic rule has no relevance for behavioral ontogeny. ... In contrast to anatomical ontogeny, in the case of behavioral ontogeny there are no empirical indications of 'behavioral interphenes, that developed phylogenetically from (primordial) behavioral metaphenes. ... These facts lead to the conclusion that attempts to establish a psychological theory on the basis of the biogenetic rule will not be fruitful. |doi=10.1159/000277108 |archive-date=2018-02-09 |archive-url=https://web.archive.org/web/20180209002823/https://www.uibk.ac.at/psychologie/humanethologie/einfuehrung-in-die-humanethologie/dateien/humandevelopment.pdf |url-status=dead }}</ref>