Editing Recapitulation theory (section)

==Embryology==

===Meckel, Serres, Geoffroy===

The idea of recapitulation was first formulated in [[biology]] from the 1790s onwards by the German [[natural philosopher]]s [[Johann Friedrich Meckel]] and [[Carl Friedrich Kielmeyer]], and by [[Étienne Serres]]<ref name="Mayr94">{{harvnb|Mayr|1994}}</ref> after which, [[Marcel Danesi]] states, it soon gained the status of a supposed [[biogenetic]] law.<ref name="Danesi93p65">{{Harv|Danesi|1993|p=65}}</ref>

The embryological theory was formalised by Serres in 1824–1826, based on Meckel's work, in what became known as the "Meckel-Serres Law". This attempted to link [[comparative embryology]] with a "pattern of unification" in the organic world. It was supported by [[Étienne Geoffroy Saint-Hilaire]], and became a prominent part of his ideas. It suggested that past transformations of life could have been through environmental causes working on the embryo, rather than on the adult as in [[Lamarckism]]. These [[naturalism (philosophy)|naturalistic]] ideas led to disagreements with [[Georges Cuvier]]. The theory was widely supported in the Edinburgh and London schools of higher anatomy around 1830, notably by [[Robert Edmond Grant]], but was opposed by [[Karl Ernst von Baer]]'s [[von Baer's laws (embryology)|ideas of divergence]], and attacked by [[Richard Owen]] in the 1830s.<ref>{{harvnb|Desmond|1989|pp=52–53, 86–88, 337–340}}</ref>

[[File:Haeckel drawings.jpg|thumb|350px|[[George Romanes]]'s 1892 copy of [[Ernst Haeckel]]'s controversial [[embryo drawing]]s{{efn|George Romanes's 1892 version of the figure is often attributed incorrectly to Haeckel.}}<ref>{{cite journal | last1=RICHARDSON | first1=MICHAEL K. | last2=KEUCK | first2=GERHARD | title=Haeckel's ABC of evolution and development | journal=Biological Reviews of the Cambridge Philosophical Society | publisher=Wiley | volume=77 | issue=4 | year=2002 | issn=1464-7931 | doi=10.1017/s1464793102005948 | pages=495–528| pmid=12475051 | s2cid=23494485 }}</ref>]]

===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>

=== Contemporary criticism ===
[[File:Wilhelm His chick brain compared to folded rubber tube.jpg|thumb|upright=1.3|Drawing by [[Wilhelm His Sr.|Wilhelm His]] of chick brain compared to folded rubber tube, 1874. Ag (Anlage) = [[Midbrain#Corpora quadrigemina|Optic lobes]], matching bulges in rubber tube.]]

Haeckel's theory and drawings were criticised by his contemporary, the anatomist [[Wilhelm His Sr.]] (1831–1904), who had developed a rival "causal-mechanical theory" of human embryonic development.<ref>{{cite web | title= Making visible embryos: Forgery charges | url= http://www.hps.cam.ac.uk/visibleembryos/s4_2.html | publisher= University of Cambridge | access-date= 27 October 2016| quote= Rütimeyer's ex-colleague, Wilhelm His, who had developed a rival, physiological embryology, which looked, not to the evolutionary past, but to bending and folding forces in the present. He now repeated and amplified the charges, and lay enemies used them to discredit the most prominent Darwinist. But Haeckel argued that his figures were schematics, not intended to be exact. They stayed in his books and were widely copied, but still attract controversy today.}}</ref><ref>{{Cite web | title= Wilhelm His, Sr | publisher= Embryo Project Encyclopedia | year= 2007 | access-date= 27 October 2016 | url= http://embryo.asu.edu/pages/wilhelm-his-sr-1831-1904 | quote= In 1874 His published his ''Über die Bildung des Lachsembryos'', an interpretation of vertebrate embryonic development. After this publication His arrived at another interpretation of the development of embryos: the concrescence theory, which claimed that at the beginning of development only the simple form of the head lies in the embryonic disk and that the axial portions of the body emerge only later.}}</ref> <!--Wilhelm -->His<!--anatomist-->'s work specifically criticised Haeckel's methodology, arguing that the shapes of embryos were caused most immediately by mechanical pressures resulting from local differences in growth. These differences were, in turn, caused by "heredity". <!--Wilhelm -->He<!-- anatomist--> compared the shapes of embryonic structures to those of rubber tubes that could be slit and bent, illustrating these comparisons with accurate drawings. [[Stephen Jay Gould]] noted in his 1977 book ''Ontogeny and Phylogeny'' that His's attack on Haeckel's recapitulation theory was far more fundamental than that of any empirical critic, as it effectively stated that Haeckel's "biogenetic law" was irrelevant.{{sfn|Gould|1977|pp=[https://archive.org/details/ontogenyphylogen00goul/page/189 189–193] |ps=: "Haeckel sensed correctly that His was a far more serious competitor than his empirical critics... His would have substituted a drastically different approach and relegated the biogenetic law to irrelevancy—a fate far worse and far more irrevocable than any odor of inaccuracy."}}<ref>{{cite journal |author= Ray, R. S. |author2=Dymecki, S. M. |title= Rautenlippe Redux -- toward a unified view of the precerebellar rhombic lip |journal= Current Opinion in Cell Biology |volume= 21 |issue= 6 |pages= 741–7 |date= December 2009 |pmid = 19883998 |pmc= 3729404 |doi= 10.1016/j.ceb.2009.10.003}}</ref>

[[File:Haeckel vs von Baer.svg|thumb|upright=2.0|Embryology theories of [[Ernst Haeckel]] and [[Karl Ernst von Baer]] compared]]

Darwin proposed that embryos resembled each other since they shared a common ancestor, which presumably had a similar embryo, but that development did not necessarily recapitulate phylogeny: he saw no reason to suppose that an embryo at any stage resembled an adult of any ancestor. Darwin supposed further that embryos were subject to less intense selection pressure than adults, and had therefore changed less.<ref>{{cite web |last1= Barnes |first1= M. Elizabeth |title= The Origin of Species: "Chapter Thirteen: Mutual Affinities of Organic Beings: Morphology: Embryology: Rudimentary Organs" (1859), by Charles R. Darwin |website= The Embryo Project Encyclopedia |url= https://embryo.asu.edu/pages/origin-species-chapter-thirteen-mutual-affinities-organic-beings-morphology-embryology |access-date= 18 April 2016}}</ref>

=== Modern status ===

Modern [[evolutionary developmental biology]] (evo-devo) follows von Baer, rather than Darwin, in pointing to active evolution of embryonic development as a significant means of changing the [[morphology (biology)|morphology]] of adult bodies. Two of the key principles of evo-devo, namely that changes in the timing ([[heterochrony]]) and positioning ([[heterotopy]]) within the body of aspects of embryonic development would change the shape of a descendant's body compared to an ancestor's, were first formulated by Haeckel in the 1870s. These elements of his thinking about development have thus survived, whereas his theory of recapitulation has not.<ref>{{cite journal |last1=Hall |first1=B. K. |title=Evo-Devo: evolutionary developmental mechanisms |journal=International Journal of Developmental Biology |date=2003 |volume=47 |issue=7–8 |pages=491–495 |pmid=14756324}}</ref>

The Haeckelian form of recapitulation theory is considered defunct.<ref name=Lovtrup>{{cite journal | last1=Lovtrup | first1=S | year=1978 | title=On von Baerian and Haeckelian Recapitulation | journal=Systematic Zoology | volume=27 | issue=3| pages=348–352 | doi=10.2307/2412887| jstor=2412887 }}</ref> Embryos do undergo a period or [[phylotypic stage]] where their morphology is strongly shaped by their phylogenetic position,<ref>{{Cite journal|last1=Drost|first1=Hajk-Georg|last2=Janitza|first2=Philipp |last3=Grosse |first3=Ivo  |last4=Quint |first4=Marcel | year=2017|title=Cross-kingdom comparison of the developmental hourglass|journal=Current Opinion in Genetics & Development|volume=45|pages=69–75|doi=10.1016/j.gde.2017.03.003|pmid=28347942|doi-access=free}}</ref> rather than selective pressures, but that means only that they resemble other embryos at that stage, not ancestral adults as Haeckel had claimed.<ref name="Kalinka2012">{{Cite journal | last1=Kalinka | first1=A. T. | last2=Tomancak | first2=P. | title=The evolution of early animal embryos: Conservation or divergence? | doi=10.1016/j.tree.2012.03.007 | journal=Trends in Ecology & Evolution | year=2012 | volume=27 | issue=7 | pages=385–393| pmid=22520868 | bibcode=2012TEcoE..27..385K }}</ref> The modern view is summarised by the [[University of California Museum of Paleontology]]:

{{Blockquote|Embryos do reflect the course of evolution, but that course is far more intricate and quirky than Haeckel claimed. Different parts of the same embryo can even evolve in different directions. As a result, the Biogenetic Law was abandoned, and its fall freed scientists to appreciate the full range of embryonic changes that evolution can produce—an appreciation that has yielded spectacular results in recent years as scientists have discovered some of the [[Evo-devo gene toolkit|specific genes that control development]].<ref>{{citation | title=Early Evolution and Development: Ernst Haeckel | series=Evolution 101 | publisher=University of California Museum of Paleontology | url=http://evolution.berkeley.edu/evosite/history/early_evodevo.shtml | access-date=2013-02-20 | url-status=dead | archive-url=https://web.archive.org/web/20121222105021/http://evolution.berkeley.edu/evosite/history/early_evodevo.shtml | archive-date=2012-12-22 }}</ref>}}