Recapitulation theory
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The '''theory of recapitulation''', also called the '''biogenetic law''' or '''embryological parallelism''', and often expressed as '''[[ontogeny]] recapitulates [[phylogeny]]''', was first put forward in 1866 by German zoologist [[Ernst Haeckel]]. Haeckel proposed that the [[embryo]]nal development of an individual organism (its ontogeny) followed the same path as the [[evolution]]ary history of its species (its phylogeny). This theory, in the highly elaborate and deterministic form advanced by Haeckel, has, since the early twentieth century, been refuted on many fronts.<ref name=Gilbert>{{cite web |url=http://8e.devbio.com/article.php?id=219 |title=Ernst Haeckel and the Biogenetic Law |accessdate=2008-05-03 |author=Scott F Gilbert |date=2006 |work=Developmental Biology, 8th edition |publisher=Sinauer Associates |quote=Eventually, the Biogenetic Law had become scientifically untenable.}}</ref> Haeckel's drawings used artistic licence, his theory was associated with [[Lamarckism]], it was quite clearly wrong in supposing that embryos passed through the adult stages of more primitive life-forms, it ignored organs such as teeth which are "held over" to a late developmental stage, and it was used by Haeckel to promote the supremacy of the white European male. However, the basic idea of recapitulation is still potent enough to have been the subject of [[Stephen Jay Gould]]'s first book, and that book begins by declaring that many medical professionals still believe, privately and informally, that there is "something in" the notion: the parallels between ontogeny and phylogeny are still one of the great themes of evolutionary biology. <ref>Stephen Jay Gould, ''Phylogeny and Ontogeny'', Harvard 1985</ref> ''(See [[Evolutionary developmental biology]])''
==Haeckel's theory==
[[Image:Haeckel drawings.jpg|thumb|350px|Romanes's 1892 copy of [[Ernst Haeckel]]'s controversial embryo drawings (this version of the figure is often attributed incorrectly to Haeckel).<ref>Richardson and Keuck, "Haeckel’s ABC of evolution and development," p. 516</ref>]]
[[Ontogeny]] is the growth (size change) and development (shape change) of an individual organism; [[Phylogenetics|phylogeny]] is the [[evolution]]ary history of a species. Haeckel's recapitulation theory claims that the development of advanced species was seen to pass through stages represented by adult organisms of more primitive species.<ref name=Gilbert /> 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 ([[Oxford English Dictionary|OED]]: 'a summing up or brief repetition').
Haeckel produced several [[embryo drawing]]s that often overemphasized similarities between embryos of related species. These found their ways into many biology textbooks, and into popular knowledge.
For example, Haeckel believed that the human embryo with [[gill slit]]s ([[pharyngeal arch]]es) in the neck not only signified a fishlike ancestor, but represented an adult "fishlike" developmental stage. Embryonic pharyngeal arches are not [[gill]]s and do not carry out the same function. They are the [[invagination]]s between the gill pouches or pharyngeal pouches, and they open the [[pharynx]] to the outside. Gill pouches appear in all [[tetrapod]] animal embryos. In [[mammal]]s, 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.<ref>{{cite web |url= http://www.palaeos.com/Vertebrates/Bones/Gill_Arches/Meckelian.html |title=The Gill Arches: Meckel's Cartilage |accessdate=2008-04-30 |author=Toby White |work=paleos.com}}</ref>
==Rejection==
Modern biology rejects the literal and universal form of Haeckel's theory.<ref name=Medicus>{{cite journal |author=Gerhard Medicus |date=1992 |title=The Inapplicability of the Biogenetic Rule to Behavioral Development |journal=Human Development |volume=35 |issue=1 |pages=1–8 |issn=0018-716X/92/0351/0001-0008 |url=http://homepage.uibk.ac.at/~c720126/humanethologie/ws/medicus/block6/HumanDevelopment.pdf |format=PDF |accessdate=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.}}</ref> Although [[Homo sapiens|humans]] are generally understood to share ancestors with other taxa, stages of human embryonic development are not functionally equivalent to the adults of these shared common ancestors. In other words, no cleanly defined and functional "fish", "reptile" and "mammal" stages of human embryonal development can be discerned. Moreover, development is nonlinear. For example, during [[kidney]] development, at one given time, the anterior region of the kidney is less developed ([[nephridium]]) than the posterior region ([[nephron]]).
Modern biology does recognize numerous connections between ontogeny and phylogeny, and explains them using evolutionary theory without recourse to Haeckel's specific views, and considers them as supporting evidence for that theory.
==Historical influence==
Although Haeckel's specific form of recapitulation theory is now discredited among biologists, it did have a strong influence on social and educational theories of the late 19th century.
English philosopher [[Herbert Spencer]] was one of the most energetic promoters of evolutionary ideas to explain pretty well everything in sight; He compactly expressed the basis for a cultural recapitulation theory of [[education]] in the following claim:<ref name="EganEducatedMind">Kieran Egan, ''The educated mind: How Cognitive Tools Shape Our Understanding.'', p.27 ([[University of Chicago Press]], 1997, Chicago. ISBN 0-226-19036-6)</ref>
{{quotation|If there be an order in which the human race has mastered its various kinds of knowledge, there will arise in every child an aptitude to acquire these kinds of knowledge in the same order.... Education is a repetition of civilization in little.<ref name="Spencer">{{cite book|author=Herbert Spencer|year=1861|title=Education|pages = p.5|url=http://www.questia.com/PM.qst?a=o&d=98953755}} </ref>|Herbert Spencer}}
The [[maturationism|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 fit nicely with other [[social Darwinism|social Darwinist]] concepts, such as the idea that "primitive" societies needed guidance by more advanced societies, i.e. Europe and North America, which were considered by social Darwinists as the pinnacle of evolution. An early form of the law was devised by the 19th-century [[Estonia]]n [[zoologist]] [[Karl Ernst von Baer]], who observed that embryos resemble the embryos, but not the adults, of other species.
== Modern observations ==
Generally, if a structure pre-dates another structure in evolutionary terms, then it also appears earlier than the other in the embryo. Species which have an evolutionary relationship typically share the early stages of embryonal development and differ in later stages. Examples include:
* The backbone, the common structure among all [[vertebrate]]s such as fish, reptiles and [[mammal]]s, appears as one of the earliest structures laid out in all vertebrate embryos.
* The [[telencephalon|cerebrum]] in [[homo sapiens|humans]], the most sophisticated part of the brain, develops last.
If a structure vanished in an evolutionary sequence, then one can often observe a corresponding structure appearing at one stage during embryonic development, only to disappear or become modified in a later stage. Examples include:
* [[Whale]]s, which have evolved from land mammals, don't have legs, but tiny remnant leg bones lie buried deep in their bodies. During embryonal development, leg extremities first occur, then recede. Similarly, whale embryos have [[hair]] at one stage (like all mammalian embryos), but lose most of it later.
* The common ancestor of humans and monkeys had a tail, and human embryos also have a tail at one point; it later recedes to form the [[coccyx]].
* The [[swim bladder]] in [[fish]] presumably evolved from a sac connected to the [[gut]], allowing the fish to gulp air. In most modern fish, this connection to the gut has disappeared. In the embryonal development of these fish, the swim bladder originates as an outpocketing of the gut, and is later disconnected from the gut.
=== Modern theory ===
One can explain connections between phylogeny and ontogeny if one assumes that one species changes into another by a sequence of small modifications to its developmental program (specified by the [[genome]]) {{Fact|date=June 2008}}. Modifications that affect early steps of this program will usually require the right modifications in later steps in order to produce an individual that survives and reproduces. Therefore, such successful combinations of changes are less likely to occur and most of the successful changes affect the latest stages of the program, and the earlier steps are retained {{Fact|date=June 2008}}. But occasionally, a modification of an earlier step in the program does succeed: for this reason ontogeny and phylogeny do not strictly correspond, contrary to Haeckel's original theory.
== Notes ==
{{Reflist}}
==References==
* {{cite web|author=Division of Biology and Medicine, Brown University |title=Evolution and Development I: Size and shape |url=http://biomed.brown.edu/Courses/BIO48/30.S&S.HTML}}
* {{cite web|author=Haeckel, E |year=1899 |title=Riddle of the Universe at the Close of the Nineteenth Century |url=http://www.ucmp.berkeley.edu/history/haeckel.html}}
* {{cite web|author=Rebecca Irwin |title=Ontogeny and Phylogeny |url=http://www.utm.edu/~rirwin/391OntogPhylog.htm}}
* {{cite journal|author=Richardson, M., et al. |year=1997 |title=There is no highly conserved stage in the vertebrates: implications for current theories of evolution and development. |journal=Anatomy and Embryology |volume=196 |issue=2 |pages=91–106 | doi = 10.1007/s004290050082 <!--Retrieved from CrossRef by DOI bot-->}}
* {{cite book|author=[[Stephen Jay Gould|Gould, Stephen Jay]] |title=Ontogeny and Phylogeny |location=Cambridge Mass. | publisher=Belknap Press of Harvard University Press |year=1977 |id=ISBN 0-674-63941-3}}
==External links==
*[http://reconstruction.eserver.org/044/vanderbeke.htm Of Parts and Wholes: Self-similarity and Synecdoche in Science, Culture and Literature]
*[http://en.wikiquote.org/wiki/Ontology "Ontology Recapitulates Philology", a parody phrase]
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