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{{redirect|Paedogenesis|the topic of soil formation|Pedogenesis}}
{{redirect|Paedogenesis|the topic of soil formation|Pedogenesis}}


'''Neoteny''' ({{IPAc-en|n|i|ˈ|ɒ|t|ən|i}}),<ref>{{cite Dictionary.com|neoteny|access-date=April 21, 2019}}</ref><ref>{{cite American Heritage Dictionary|neoteny|access-date=April 21, 2019}}</ref><ref>{{Cite dictionary |url=http://www.lexico.com/en/definition/neoteny |archive-url=https://web.archive.org/web/20200322182027/https://www.lexico.com/en/definition/neoteny |url-status=dead |archive-date=2020-03-22 |title=neoteny |dictionary=[[Lexico]] US English Dictionary |publisher=[[Oxford University Press]]}}</ref><ref>{{cite Merriam-Webster|neoteny|access-date=April 21, 2019}}</ref> also called '''juvenilization''',<ref name="Montagu">Montagu, A. (1989). Growing Young. Bergin & Garvey: CT.</ref> is the delaying or slowing of the [[Physiology|physiological]], or [[Somatic (biology)|somatic]], development of an organism, typically an animal. Neoteny is found in [[Neoteny in humans|modern humans]] compared to other primates.<ref>{{cite magazine|url=http://www.scientificamerican.com/article/being-more-infantile/|title=Being More Infantile May Have Led to Bigger Brains|first=Charles Q.|last=Choi|date=1 July 2009|magazine=[[Scientific American]]}}</ref> In '''progenesis''' or '''paedogenesis''', [[sexual development]] is accelerated.<ref>Volkenstein, M. V. 1994. ''Physical Approaches to Biological Evolution''. Springer-Verlag: Berlin, [https://books.google.com/books?id=iiT7CAAAQBAJ&pg=PA87].</ref>
'''Neoteny''' ({{IPAc-en|n|i|ˈ|ɒ|t|ən|i}}),<ref>{{cite Dictionary.com|neoteny|access-date=21 April 2019}}</ref><ref>{{cite American Heritage Dictionary|neoteny|access-date=21 April 2019}}</ref><ref>{{Cite dictionary |url=http://www.lexico.com/en/definition/neoteny |archive-url=https://web.archive.org/web/20200322182027/https://www.lexico.com/en/definition/neoteny |url-status=dead |archive-date=22 March 2020 |title=neoteny |dictionary=[[Lexico]] US English Dictionary |publisher=[[Oxford University Press]]}}</ref><ref>{{cite Merriam-Webster|neoteny|access-date=21 April 2019}}</ref> also called '''juvenilization''',<ref name="Montagu">Montagu, A. (1989). Growing Young. Bergin & Garvey: CT.</ref> is the delaying or slowing of the [[Physiology|physiological]], or [[Somatic (biology)|somatic]], development of an organism, typically an animal. [[Neoteny in humans|Neoteny in modern humans]] is more significant than in other primates.<ref>{{cite magazine |last=Choi |first=Charles Q. |url=http://www.scientificamerican.com/article/being-more-infantile/ |title=Being More Infantile May Have Led to Bigger Brains |date=1 July 2009 |magazine=[[Scientific American]]}}</ref> In '''progenesis''' or '''paedogenesis''', [[sexual development]] is accelerated.<ref>Volkenstein, M. V. 1994. ''Physical Approaches to Biological Evolution''. Springer-Verlag: Berlin, [https://books.google.com/books?id=iiT7CAAAQBAJ&pg=PA87].</ref>


Both neoteny and progenesis result in '''paedomorphism'''<ref>{{cite web | url=https://en.wiktionary.org/wiki/paedomorphic | title=Paedomorphic | date=21 January 2022 }}</ref> (as having the form typical of children) or '''paedomorphosis'''<ref>{{cite web | url=https://en.wiktionary.org/wiki/morphosis | title=Morphosis | date=6 June 2022 }}</ref> (changing towards forms typical of children), a type of [[heterochrony]].<ref name="Ridley">{{cite book |author=Ridley, Mark |url=http://www.blackwellpublishing.com/ridley/a-z/Neoteny.asp |title=Evolution |publisher=Blackwell |date=1985 }}</ref> It is the retention in adults of traits previously seen only in the young. Such retention is important in [[evolutionary biology]], [[domestication]] and [[evolutionary developmental biology]]. Some authors define paedomorphism as the retention of [[larval]] traits, as seen in [[salamanders]].<ref>{{cite journal | last1=Whiteman | first1=H.H. | year=1994 | title=Evolution of facultative paedomorphosis| journal=Quarterly Review of Biology | volume=69 | issue=2 | pages=205–221 | doi=10.1086/418540| s2cid=83500486 }}</ref><ref name="Schell">Schell, S. C. ''Handbook of Trematodes of North America North of Mexico'', 1985, pg. 22</ref><ref>Ginetsinskaya, T.A. ''Trematodes, Their Life Cycles, Biology and Evolution''. Leningrad, USSR: Nauka 1968. Translated in 1988, [https://books.google.com/books?id=JxZDAAAAYAAJ].</ref>
Both neoteny and progenesis result in '''paedomorphism'''<ref>{{cite web |url=https://en.wiktionary.org/wiki/paedomorphic |title=Paedomorphic |date=21 January 2022 }}</ref> (as having the form typical of children) or '''paedomorphosis'''<ref>{{cite web |url=https://en.wiktionary.org/wiki/morphosis |title=Morphosis |date=6 June 2022 }}</ref> (changing towards forms typical of children), a type of [[heterochrony]].<ref name="Ridley">{{cite book |last=Ridley |first=Mark |title=Evolution |url=http://www.blackwellpublishing.com/ridley/a-z/Neoteny.asp |publisher=Blackwell |date=1985 }}</ref> It is the retention in adults of traits previously seen only in the young. Such retention is important in [[evolutionary biology]], [[domestication]], and [[evolutionary developmental biology]]. Some authors define paedomorphism as the retention of [[larval]] traits, as seen in [[salamanders]].<ref>{{cite journal |last=Whiteman |first=H.H. |year=1994 |title=Evolution of facultative paedomorphosis |journal=Quarterly Review of Biology |volume=69 |issue=2 |pages=205–221 |doi=10.1086/418540 |s2cid=83500486 }}</ref><ref name="Schell">Schell, S. C. ''Handbook of Trematodes of North America North of Mexico'', 1985, pg. 22</ref><ref>Ginetsinskaya, T.A. ''Trematodes, Their Life Cycles, Biology and Evolution''. Leningrad, USSR: Nauka 1968. Translated in 1988, [https://books.google.com/books?id=JxZDAAAAYAAJ].</ref>


== History and etymology ==
== History and etymology ==
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[[File:Heterochrony.svg|thumb|upright=2|Diagram of the six types of shift in [[heterochrony]], a change in the timing or rate of any process in [[embryonic development]]. Predisplacement, hypermorphosis, and acceleration (red) extend development ([[peramorphosis]]); postdisplacement, hypomorphosis, and deceleration (blue) all truncate it (paedomorphosis).]]
[[File:Heterochrony.svg|thumb|upright=2|Diagram of the six types of shift in [[heterochrony]], a change in the timing or rate of any process in [[embryonic development]]. Predisplacement, hypermorphosis, and acceleration (red) extend development ([[peramorphosis]]); postdisplacement, hypomorphosis, and deceleration (blue) all truncate it (paedomorphosis).]]


The origins of the concept of neoteny have been traced to biblical times{{vague|date=September 2021}} (as argued by [[Ashley Montagu]])<ref>{{cite book |last1=Montagu |first1=Ashley |title=Growing Young |date=1989 |publisher=Bloomsbury Academic |isbn=978-0-89789-167-7 |url=https://www.google.com/books/edition/Growing_Young/9IUtAAAAMAAJ |access-date=17 January 2024 |language=en}}</ref> and to the poet [[William Wordsworth]]'s "[[My Heart Leaps Up|The Child is the father of the Man]]" (as argued by [[Barry Bogin]]).<ref>{{cite journal |last1=Bogin |first1=Barry |author1-link=Barry Bogin |title=Evolutionary hypotheses for human childhood |journal=Cover Image American Journal of Physical Anthropology |date=6 December 1998 |volume=104 |issue=S25 |page=66 |doi=10.1002/(SICI)1096-8644(1997)25+%3C63::AID-AJPA3%3E3.0.CO;2-8 |url=https://onlinelibrary.wiley.com/doi/abs/10.1002/(SICI)1096-8644(1997)25+%3C63::AID-AJPA3%3E3.0.CO;2-8 |access-date=17 January 2024 |publisher=Wiley Periodicals LLC |language=en-US |issn=0002-9483 |quote=William Wordsworth, for example, praised the concept of neoteny in 1802 with words of innocence and hope|hdl=2027.42/37682 |hdl-access=free }}</ref> The term itself was invented in 1885 by [[Julius Kollmann]] as he described the [[axolotl]]'s maturation while remaining in a [[tadpole]]-like aquatic stage complete with gills, unlike other adult [[amphibians]] like frogs and toads.<ref>{{cite journal |last1=Kollmann |first1=J. |title=Das Ueberwintern von europäischen Frosch- und Tritonlarven und die Umwandlung des mexikanischen Axolotl |journal=Verhandlungen der Naturforschenden Gesellschaft in Basel (Proceedings of the Natural Science Society of Basel) |date=1885 |volume=7 |pages=387–398 |url=https://www.biodiversitylibrary.org/item/42693#page/397/mode/1up |trans-title=The overwintering of European frog- and triton larvae and the transformation of the Mexican axolotl |language=German}} From pp. 397–398: ''"Dann drängt sich die Frage auf, ob das Latenzstadium der Eier, das einerseits bei Fischen, Vögeln and Säugethieren in so höchst überraschenden Formen vorkommt, anderseits das Latenzstadium bei den Wirbellosen ¹) nicht eine Variante derselben Eigenschaft der Organismen sei, welche ich Neotenie genannt habe, und die auf irgend einer Entwichlungsstufe in Kraft treten kann."'' (Then the question arises whether on the one hand the latency stage of eggs — which occurs in such highly surprising forms in fish, birds and mammals — [and] on the other hand the latency stage in invertebrates ¹) be not a variant of the same property of the organisms, which I have called "neoteny" and which can come into force at any stage of development.)</ref><ref name="Bogin1999">{{cite book |last=Bogin |first=Barry |title=Patterns of Human Growth |url=https://books.google.com/books?id=ScfPjwF3BngC&pg=PA158 |year=1999 |publisher=Cambridge University Press |isbn=978-0-521-56438-0 |pages=157–169}}</ref>
[[Julius Kollmann]] created the term "neoteny" in 1885 after he described the [[axolotl]]'s maturation while remaining in a [[tadpole]]-like aquatic stage complete with gills, unlike other adult [[amphibians]] like frogs and toads.<ref>{{cite journal |last=Kollmann |first=J. |title=Das Ueberwintern von europäischen Frosch- und Tritonlarven und die Umwandlung des mexikanischen Axolotl |journal=Verhandlungen der Naturforschenden Gesellschaft in Basel (Proceedings of the Natural Science Society of Basel) |date=1885 |volume=7 |pages=387–398 |url=https://www.biodiversitylibrary.org/item/42693#page/397/mode/1up |trans-title=The overwintering of European frog- and triton larvae and the transformation of the Mexican axolotl |language=German}} From pp. 397–398: ''"Dann drängt sich die Frage auf, ob das Latenzstadium der Eier, das einerseits bei Fischen, Vögeln and Säugethieren in so höchst überraschenden Formen vorkommt, anderseits das Latenzstadium bei den Wirbellosen ¹) nicht eine Variante derselben Eigenschaft der Organismen sei, welche ich Neotenie genannt habe, und die auf irgend einer Entwichlungsstufe in Kraft treten kann."'' (Then the question arises whether on the one hand the latency stage of eggs — which occurs in such highly surprising forms in fish, birds and mammals — [and] on the other hand the latency stage in invertebrates ¹) be not a variant of the same property of the organisms, which I have called "neoteny" and which can come into force at any stage of development.)</ref><ref name="Bogin1999">{{cite book |last=Bogin |first=Barry |title=Patterns of Human Growth |url=https://books.google.com/books?id=ScfPjwF3BngC&pg=PA158 |year=1999 |publisher=Cambridge University Press |isbn=978-0-521-56438-0 |pages=157–169}}</ref>


The word ''neoteny'' is borrowed from the [[German language|German]] ''Neotenie'', the latter constructed by Kollmann from the [[Greek language|Greek]] νέος (''neos'', "young") and τείνειν (''teínein'', "to stretch, to extend"). The [[adjective]] is either "neotenic" or "neotenous".<ref>[http://www.thefreedictionary.com/neoteny Neoteny], ''The Free Dictionary''. 2011. Accessed April 30, 2011.</ref> For the opposite of "neotenic", different authorities use either "gerontomorphic"<ref name="Henke">Henke, W. (2007). Handbook of paleoanthropology, Volume 1. Springer Books, NY.</ref><ref name="Hether">Hetherington, R. (2010). The Climate Connection: Climate Change and Modern Human Evolution. Cambridge University Press.</ref> or "[[peramorphosis|peramorphic]]".<ref name="Hall">Hall, B.K., Hallgrímsson, B. Monroe, W.S. (2008). Strickberger's evolution: the integration of genes, organisms and populations. Jones and Bartlett Publishers: Canada.</ref> Bogin points out that Kollmann had intended the meaning to be "retaining youth", but had evidently confused the Greek ''teínein'' with the Latin ''tenere'', which had the meaning he wanted, "to retain", so that the new word would mean "the retaining of youth (into adulthood)".<ref name="Bogin1999" />
The word ''neoteny'' is borrowed from the [[German language|German]] ''Neotenie'', the latter constructed by Kollmann from the [[Greek language|Greek]] νέος (''neos'', "young") and τείνειν (''teínein'', "to stretch, to extend"). The [[adjective]] is either "neotenic" or "neotenous".<ref>[http://www.thefreedictionary.com/neoteny Neoteny], ''The Free Dictionary''. 2011. Accessed April 30, 2011.</ref> For the opposite of "neotenic", different authorities use either "gerontomorphic"<ref name="Henke">Henke, W. (2007). Handbook of paleoanthropology, Volume 1. Springer Books, NY.</ref><ref name="Hether">Hetherington, R. (2010). The Climate Connection: Climate Change and Modern Human Evolution. Cambridge University Press.</ref> or "[[peramorphosis|peramorphic]]".<ref name="Hall">Hall, B.K., Hallgrímsson, B. Monroe, W.S. (2008). Strickberger's evolution: the integration of genes, organisms and populations. Jones and Bartlett Publishers: Canada.</ref> Bogin points out that Kollmann had intended the meaning to be "retaining youth", but had evidently confused the Greek ''teínein'' with the Latin ''tenere'', which had the meaning he wanted, "to retain", so that the new word would mean "the retaining of youth (into adulthood)".<ref name="Bogin1999" />


In 1926, [[Louis Bolk]] described neoteny as the major process in humanization.<ref>{{cite book |last1=Bolk |first1=Louis |title=Das Problem der Menschwerdung : Vortrag gehalten am 15. April 1926 auf der XXV. Versammlung der anatomischen Gesellschaft zu Freiburg |trans-title=The Problem of Humanization: Lecture held on 15 April 1926 at the 25th Congress of the Anatomical Society at Freiberg |date=1926 |publisher=Gustav Fischer |location=Jena, Germany |language=German}}</ref><ref name="Bogin1999" /> In his 1977 book ''[[Ontogeny and Phylogeny]]'',<ref>{{cite book |last1=Gould |first1=Stephen Jay |title=Ontogeny and Phylogeny |date=1977 |publisher=Belknap (Harvard University Press) |location=Cambridge, Massachusetts |isbn=978-0-674-63940-9 |url=https://archive.org/details/ontogenyphylogen00goul }}</ref> [[Stephen Jay Gould]] noted that Bolk's account constituted an attempted justification for "scientific" racism and sexism, but acknowledged that Bolk had been right in the core idea that humans differ from other [[primates]] in becoming sexually mature in an infantile stage of body development.<ref name="Bogin1999" />
In 1926, [[Louis Bolk]] described neoteny as the major process in humanization.<ref>{{cite book |last=Bolk |first=Louis |title=Das Problem der Menschwerdung : Vortrag gehalten am 15. April 1926 auf der XXV. Versammlung der anatomischen Gesellschaft zu Freiburg |trans-title=The Problem of Humanization: Lecture held on 15 April 1926 at the 25th Congress of the Anatomical Society at Freiberg |date=1926 |publisher=Gustav Fischer |location=Jena, Germany |language=German}}</ref><ref name="Bogin1999" /> In his 1977 book ''[[Ontogeny and Phylogeny]]'',<ref>{{cite book |last1=Gould |first1=Stephen Jay |title=Ontogeny and Phylogeny |date=1977 |publisher=Belknap (Harvard University Press) |location=Cambridge, Massachusetts |isbn=978-0-674-63940-9 |url=https://archive.org/details/ontogenyphylogen00goul }}</ref> [[Stephen Jay Gould]] noted that Bolk's account constituted an attempted justification for "scientific" racism and sexism, but acknowledged that Bolk had been right in the core idea that humans differ from other [[primates]] in becoming sexually mature in an infantile stage of body development.<ref name="Bogin1999" />


== In humans ==
== In humans ==
{{main|Neoteny in humans}}
{{main|Neoteny in humans}}


Neoteny in humans is the slowing or delaying of body development, compared to non-human [[primates]], resulting in features such as a large head, a flat face, and relatively short arms. These neotenic changes may have been brought about by [[sexual selection in human evolution]]. In turn, they may have permitted the development of human capacities such as emotional communication. However, humans also have relatively large noses and long legs, both [[peramorphic]] (not neotenic) traits. Some evolutionary theorists have proposed that neoteny was a key feature in [[human evolution]].<ref>{{cite journal |last1=Shea |first1=Brian T. |title=Heterochrony in human evolution: The case for neoteny reconsidered |journal=American Journal of Physical Anthropology |date=1989 |volume=32 |issue=S10 |pages=69–101 |doi=10.1002/ajpa.1330320505}}</ref> [[J. B. S. Haldane]] states a "major evolutionary trend in human beings" is "greater prolongation of childhood and retardation of maturity."<ref name="Montagu" /> [[Del Thiessen|Delbert D. Thiessen]] said that "neoteny becomes more apparent as early primates evolved into later forms" and that primates have been "evolving toward flat face."<ref name="Bitter">Thiessen, D.D. (1997). Bittersweet destiny: the stormy evolution of human behavior. Transaction Publishers, N.J.</ref> Doug Jones argued that human evolution's trend toward neoteny may have been caused by sexual selection in human evolution for neotenous facial traits in women by men with the resulting neoteny in male faces being a "by-product" of [[sexual selection]] for neotenous female faces.<ref name="DJones">{{cite journal | last1=Jones | first1=D. | display-authors=etal | year=1995 | title=Sexual selection, physical attractiveness, and facial neoteny: Cross-cultural evidence and implications [and comments and reply] | url=https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1601&context=fchd_facpub| journal=Current Anthropology | volume=36 | issue=5| pages=723–748 | doi=10.1086/204427| s2cid=52840802 }}</ref>
Neoteny in humans is the slowing or delaying of body development, compared to non-human [[primates]], resulting in features such as a large head, a flat face, and relatively short arms. These neotenic changes may have been brought about by [[sexual selection in human evolution]]. In turn, they may have permitted the development of human capacities such as emotional communication. Some evolutionary theorists have proposed that neoteny was a key feature in [[human evolution]].<ref>{{cite journal |last=Shea |first=Brian T. |title=Heterochrony in human evolution: The case for neoteny reconsidered |journal=American Journal of Physical Anthropology |date=1989 |volume=32 |issue=S10 |pages=69–101 |doi=10.1002/ajpa.1330320505}}</ref> [[J. B. S. Haldane]] states a "major evolutionary trend in human beings" is "greater prolongation of childhood and retardation of maturity."<ref name="Montagu" /> [[Del Thiessen|Delbert D. Thiessen]] said that "neoteny becomes more apparent as early primates evolved into later forms" and that primates have been "evolving toward flat face."<ref name="Bitter">Thiessen, D.D. (1997). Bittersweet destiny: the stormy evolution of human behavior. Transaction Publishers, N.J.</ref> Doug Jones argued that human evolution's trend toward neoteny may have been caused by sexual selection in human evolution for neotenous facial traits in women by men with the resulting neoteny in male faces being a "by-product" of [[sexual selection]] for neotenous female faces.<ref name="DJones">{{cite journal |last1=Jones |first1=D. |display-authors=etal |year=1995 |title=Sexual selection, physical attractiveness, and facial neoteny: Cross-cultural evidence and implications [and comments and reply] |url=https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1601&context=fchd_facpub|journal=Current Anthropology |volume=36 |issue=5 |pages=723–748 |doi=10.1086/204427 |s2cid=52840802 }}</ref>


== In domestic animals ==
== In domestic animals ==

{{further|Domestication of animals}}
{{further|Domestication of animals}}


Neoteny is seen in domesticated animals such as dogs and mice.<ref name="sciencedirect.com">{{cite journal | last1=Price | first1=E. | year=1999 | title=Behavioral development in animals undergoing domestication | journal=Applied Animal Behaviour Science | volume=65 | issue=3| pages=245–271 | doi=10.1016/S0168-1591(99)00087-8}}</ref> This is because there are more resources available, less competition for those resources, and with the lowered competition the animals expend less energy obtaining those resources. This allows them to mature and reproduce more quickly than their wild counterparts.<ref name="sciencedirect.com" /> The environment that domesticated animals are raised in determines whether or not neoteny is present in those animals. Evolutionary neoteny can arise in a species when those conditions occur, and a species becomes sexually mature ahead of its "normal development". Another explanation for the neoteny in domesticated animals can be the selection for certain behavioral characteristics. Behavior is linked to genetics which therefore means that when a behavioral trait is selected for, a physical trait may also be selected for due to mechanisms like [[linkage disequilibrium]]. Often, juvenile behaviors are selected for in order to more easily domesticate a species; aggressiveness in certain species comes with adulthood when there is a need to compete for resources. If there is no need for competition, then there is no need for aggression. Selecting for juvenile behavioral characteristics can lead to neoteny in physical characteristics because, for example, with the reduced need for behaviors like aggression, there is no need for developed traits that would help in that area. Traits that may become neotenized due to decreased aggression may be a shorter muzzle and smaller general size among the domesticated individuals. Some common neotenous physical traits in domesticated animals (mainly dogs, pigs, ferrets, cats, and even foxes) include floppy ears, changes in the reproductive cycle, curly tails, [[piebald]] coloration, fewer or shortened vertebra, large eyes, rounded forehead, large ears, and shortened muzzle.<ref name="Bertone, J. 2006">Bertone, J. (2006). Equine geriatric medicine and surgery. Saunders, MI.</ref><ref>{{cite journal | last1=Trut | first1=L. N. | year=1999 | title=Early canid domestication: the farm-fox experiment | journal=American Scientist | volume=87 | issue=2| pages=160–169 | doi=10.1511/1999.2.160| bibcode=1999AmSci..87.....T }}</ref>
Neoteny is seen in domesticated animals such as dogs and mice.<ref name="sciencedirect.com">{{cite journal |last=Price |first=E. |year=1999 |title=Behavioral development in animals undergoing domestication |journal=Applied Animal Behaviour Science |volume=65 |issue=3 |pages=245–271 |doi=10.1016/S0168-1591(99)00087-8}}</ref> This is because there are more resources available, less competition for those resources, and with the lowered competition the animals expend less energy obtaining those resources. This allows them to mature and reproduce more quickly than their wild counterparts.<ref name="sciencedirect.com" /> The environment that domesticated animals are raised in determines whether or not neoteny is present in those animals. Evolutionary neoteny can arise in a species when those conditions occur, and a species becomes sexually mature ahead of its "normal development". Another explanation for the neoteny in domesticated animals can be the selection for certain behavioral characteristics. Behavior is linked to genetics which therefore means that when a behavioral trait is selected for, a physical trait may also be selected for due to mechanisms like [[linkage disequilibrium]]. Often, juvenile behaviors are selected for in order to more easily domesticate a species; aggressiveness in certain species comes with adulthood when there is a need to compete for resources. If there is no need for competition, then there is no need for aggression. Selecting for juvenile behavioral characteristics can lead to neoteny in physical characteristics because, for example, with the reduced need for behaviors like aggression, there is no need for developed traits that would help in that area. Traits that may become neotenized due to decreased aggression may be a shorter muzzle and smaller general size among the domesticated individuals. Some common neotenous physical traits in domesticated animals (mainly rabbits, dogs, pigs, ferrets, cats, and even foxes) include floppy ears, changes in the reproductive cycle, curly tails, [[piebald]] coloration, fewer or shortened vertebra, large eyes, rounded forehead, large ears, and shortened muzzle.<ref>{{cite book |last1=Vonk |first1=Jennifer |last2=Shackelford |first2=Todd |chapter=Neoteny |title=Encyclopedia of Animal Cognition and Behavior |publisher=Springer |date=1 April 2022 |pages=4590–4592 |isbn=978-3-319-55064-0 }}</ref><ref name="Bertone, J. 2006">Bertone, J. (2006). Equine geriatric medicine and surgery. Saunders, MI.</ref><ref>{{cite journal |last=Trut |first=L. N. |year=1999 |title=Early canid domestication: the farm-fox experiment |journal=American Scientist |volume=87 |issue=2 |pages=160–169 |doi=10.1511/1999.2.160 |bibcode=1999AmSci..87.....T }}</ref>


[[File:Unnatural selection, 2 heads, one species.jpg|thumb|Neoteny and reduction in skull size – [[grey wolf]] and [[chihuahua dog|chihuahua]] skulls]]
[[File:Unnatural selection, 2 heads, one species.jpg|thumb|Neoteny and reduction in skull size – [[grey wolf]] and [[chihuahua dog|chihuahua]] skulls]]
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When the role of dogs expanded from just being [[Working Group (dogs)|working dogs]] to also being [[companion dog|companions]], humans started [[selective breeding]] dogs for [[Morphology (biology)|morphological]] neoteny, and this selective breeding for "neoteny or paedomorphism" "strengthened the human-canine bond."<ref name="McGreevy" /> Humans bred dogs to have more "juvenile physical traits" as adults, such as short snouts and wide-set eyes which are associated with puppies because people usually consider these traits to be more attractive.<!-- This is on the bottom of page 167. --> Some breeds of dogs with short snouts and broad heads such as the [[Komondor]], [[St. Bernard (dog)|Saint Bernard]] and [[Maremma Sheepdog]] are more morphologically neotenous than other breeds of dogs.<!-- This is in the second paragraph of page 170. --><ref>Beck, A.M. & Katcher, A.H. (1996). Between Pets and People: The Importance of Companionship. West Lafayette, Indiana: Purdue University Press. {{ISBN|1-55753-077-7}}</ref> [[Cavalier King Charles spaniel]]s are an example of selection for neoteny because they exhibit large eyes, pendant-shaped ears and compact feet, giving them a morphology similar to puppies as adults.<!-- This is on page 332 in the second paragraph. --><ref name="McGreevy">McGreevy, P.D. & Nicholas, F.W. (1999). Some Practical Solutions to Welfare Problems in Dog Breeding. In Animal Welfare. 8: 329–341.</ref>
When the role of dogs expanded from just being [[Working Group (dogs)|working dogs]] to also being [[companion dog|companions]], humans started [[selective breeding]] dogs for [[Morphology (biology)|morphological]] neoteny, and this selective breeding for "neoteny or paedomorphism" "strengthened the human-canine bond."<ref name="McGreevy" /> Humans bred dogs to have more "juvenile physical traits" as adults, such as short snouts and wide-set eyes which are associated with puppies because people usually consider these traits to be more attractive.<!-- This is on the bottom of page 167. --> Some breeds of dogs with short snouts and broad heads such as the [[Komondor]], [[St. Bernard (dog)|Saint Bernard]] and [[Maremma Sheepdog]] are more morphologically neotenous than other breeds of dogs.<!-- This is in the second paragraph of page 170. --><ref>Beck, A.M. & Katcher, A.H. (1996). Between Pets and People: The Importance of Companionship. West Lafayette, Indiana: Purdue University Press. {{ISBN|1-55753-077-7}}</ref> [[Cavalier King Charles spaniel]]s are an example of selection for neoteny because they exhibit large eyes, pendant-shaped ears and compact feet, giving them a morphology similar to puppies as adults.<!-- This is on page 332 in the second paragraph. --><ref name="McGreevy">McGreevy, P.D. & Nicholas, F.W. (1999). Some Practical Solutions to Welfare Problems in Dog Breeding. In Animal Welfare. 8: 329–341.</ref>


In 2004, a study that used 310 wolf skulls and over 700 dog skulls representing 100 breeds concluded that the evolution of dog skulls can generally not be described by heterochronic processes such as neoteny, although some pedomorphic dog breeds have skulls that resemble the skulls of juvenile wolves.<ref>Drake, Abby Grace, "Evolution and development of the skull morphology of canids: An investigation of morphological integration and heterochrony" (January 1, 2004). Doctoral Dissertations Available from Proquest. Paper AAI3136721. [http://scholarworks.umass.edu/dissertations/AAI3136721 link]</ref> By 2011, the findings by the same researcher were simply "Dogs are not paedomorphic wolves."<ref>{{cite journal|doi=10.1111/j.1525-142X.2011.00470.x|pmid=21410876|title=Dispelling dog dogma: An investigation of heterochrony in dogs using 3D geometric morphometric analysis of skull shape|journal=Evolution & Development|volume=13|issue=2|pages=204–213|year=2011|last1=Drake|first1=Abby Grace|s2cid=20893501}}</ref>
In 2004, a study that used 310 wolf skulls and over 700 dog skulls representing 100 breeds concluded that the evolution of dog skulls can generally not be described by heterochronic processes such as neoteny, although some pedomorphic dog breeds have skulls that resemble the skulls of juvenile wolves.<ref>Drake, Abby Grace, "Evolution and development of the skull morphology of canids: An investigation of morphological integration and heterochrony" (January 1, 2004). Doctoral Dissertations Available from Proquest. Paper AAI3136721. [http://scholarworks.umass.edu/dissertations/AAI3136721 link]</ref> By 2011, the findings by the same researcher were simply "Dogs are not paedomorphic wolves."<ref>{{cite journal |last1=Drake |first1=Abby Grace |doi=10.1111/j.1525-142X.2011.00470.x |pmid=21410876 |title=Dispelling dog dogma: An investigation of heterochrony in dogs using 3D geometric morphometric analysis of skull shape |journal=Evolution & Development |year=2011 |volume=13 |issue=2 |pages=204–213 |s2cid=20893501}}</ref>


== In other species ==
== In other species ==
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[[File:Axolotl ganz.jpg|thumb|alt=A green salamander with four short legs|The axolotl is a neotenous [[salamander]], often retaining gills throughout its life.]]
[[File:Axolotl ganz.jpg|thumb|alt=A green salamander with four short legs|The axolotl is a neotenous [[salamander]], often retaining gills throughout its life.]]


Neoteny has been observed in many other species. It is important to note the difference between partial and full neoteny when looking at other species, to distinguish between juvenile traits which are advantageous in the short term and traits which are beneficial throughout the organism's life; this might provide insight into the cause of neoteny in a species. Partial neoteny is the retention of the larval form beyond the usual age of maturation, with possible sexual development (progenesis) and eventual maturation into the adult form; this is seen in the frog ''[[Lithobates clamitans]]''. Full neoteny is seen in ''[[Axolotl|Ambystoma mexicanum]]'' and some populations of ''[[Tiger salamander|Ambystoma tigrinum]]'', which remain in larval form throughout their lives.<ref name="Swingle, W. 1922 pp.397-421">{{cite journal | last1=Swingle | first1=W. | year=1922 | title=Experiments on the metamorphosis of neotenous amphibians | url=https://zenodo.org/record/1426890| journal=Journal of Experimental Zoology | volume=36 | issue=4| pages=397–421 | doi=10.1002/jez.1400360402 }}</ref><ref>{{cite web|url=http://amphibiaweb.org/species/3850|title=Ambystoma tigrinum|publisher=Amphibia Web}}</ref> ''Lithobates clamitans'' is partially neotenous; it delays maturation during the winter as fewer resources are available; it can find resources more easily in its larval form. This encompasses both of the main causes of neoteny; the energy required to survive in the winter as a newly-formed adult is too great, so the organism exhibits neotenous characteristics until it can better survive as an adult. ''Ambystoma tigrinum'' retains its neoteny for a similar reason; however, the retention is permanent due to the lack of available resources throughout its lifetime. This is another example of an environmental cause of neoteny. Several avian species, such as the [[manakin]]s ''[[Long-tailed manakin|Chiroxiphia linearis]]'' and ''[[Blue manakin|Chiroxiphia caudata]]'', exhibit partial neoteny. The males of both species retain juvenile plumage into adulthood, losing it when they are fully mature.<ref>{{cite journal | last1=Foster | first1=M. | year=1987 | title=Delayed maturation, neoteny, and social system differences in two manakins of genus ''Chiroxyphia'' | url=https://zenodo.org/record/1235115| journal=Evolution | volume=41 | issue=3| pages=547–558 | doi=10.2307/2409256| pmid=28563802 | jstor=2409256 }}</ref> In some bird species, the retention of juvenile plumage is linked to the molting time in each species. To ensure no overlap between molting and mating times, the birds may exhibit partial neoteny in plumage; males do not attain their bright, adult plumage before the females are prepared to mate. Neoteny is present because there is no need for the males to molt early, and trying to mate with immature females would be energy-inefficient.
Neoteny has been observed in many other species. It is important to note the difference between partial and full neoteny when looking at other species, to distinguish between juvenile traits which are advantageous in the short term and traits which are beneficial throughout the organism's life; this might provide insight into the cause of neoteny in a species. Partial neoteny is the retention of the larval form beyond the usual age of maturation, with possible sexual development (progenesis) and eventual maturation into the adult form; this is seen in the frog ''[[Lithobates clamitans]]''. Full neoteny is seen in ''[[Axolotl|Ambystoma mexicanum]]'' and some populations of ''[[Tiger salamander|Ambystoma tigrinum]]'', which remain in larval form throughout their lives.<ref name="Swingle, W. 1922 pp.397-421">{{cite journal |last=Swingle |first=W. |year=1922 |title=Experiments on the metamorphosis of neotenous amphibians |url=https://zenodo.org/record/1426890|journal=Journal of Experimental Zoology |volume=36 |issue=4 |pages=397–421 |doi=10.1002/jez.1400360402 |bibcode=1922JEZ....36..397S }}</ref><ref>{{cite web |url=http://amphibiaweb.org/species/3850 |title=Ambystoma tigrinum |publisher=Amphibia Web}}</ref> ''Lithobates clamitans'' is partially neotenous; it delays maturation during the winter as fewer resources are available; it can find resources more easily in its larval form. This encompasses both of the main causes of neoteny; the energy required to survive in the winter as a newly-formed adult is too great, so the organism exhibits neotenous characteristics until it can better survive as an adult. ''Ambystoma tigrinum'' retains its neoteny for a similar reason; however, the retention is permanent due to the lack of available resources throughout its lifetime. This is another example of an environmental cause of neoteny. Several avian species, such as the [[manakin]]s ''[[Long-tailed manakin|Chiroxiphia linearis]]'' and ''[[Blue manakin|Chiroxiphia caudata]]'', exhibit partial neoteny. The males of both species retain juvenile plumage into adulthood, losing it when they are fully mature.<ref>{{cite journal |last=Foster |first=M. |year=1987 |title=Delayed maturation, neoteny, and social system differences in two manakins of genus ''Chiroxyphia'' |url=https://zenodo.org/record/1235115|journal=Evolution |volume=41 |issue=3|pages=547–558 |doi=10.2307/2409256|pmid=28563802 |jstor=2409256 }}</ref>


Neoteny is commonly seen in flightless insects, such as the females of the order [[Strepsiptera]]. Flightlessness in insects has evolved separately a number of times; factors which may have contributed to the separate evolution of flightlessness are high altitude, geographic isolation (islands), and low temperatures.<ref name="Barbosa, P. 1989">{{cite journal | last1=Barbosa | first1=P. | display-authors=etal | year=1989 | title=Life-history traits of forest-inhabiting flightless Lepidoptera | journal=American Midland Naturalist | volume=122 | issue=2| pages=262–274 | jstor=2425912 | doi=10.2307/2425912}}</ref> Under these environmental conditions, dispersal would be disadvantageous; heat is lost more rapidly through wings in colder climates. The [[Larviform female|females]] of certain insect groups become sexually mature without metamorphosis, and some do not develop wings. Flightlessness in some female insects has been linked to higher [[fecundity]].<ref name="Barbosa, P. 1989" /> [[Aphid]]s are an example of insects which may never develop wings, depending on their environment. If resources are abundant on a host plant, there is no need to grow wings and disperse. If resources become diminished, their offspring may develop wings to disperse to other host plants.<ref name="Harrison1980" />
Neoteny is commonly seen in flightless insects, such as the females of the order [[Strepsiptera]]. Flightlessness in insects has evolved separately a number of times; factors which may have contributed to the separate evolution of flightlessness are high altitude, geographic isolation (islands), and low temperatures.<ref name="Barbosa, P. 1989">{{cite journal |last1=Barbosa |first1=P. |display-authors=etal |year=1989 |title=Life-history traits of forest-inhabiting flightless Lepidoptera |journal=American Midland Naturalist |volume=122 |issue=2|pages=262–274 |jstor=2425912 |doi=10.2307/2425912}}</ref> Under these environmental conditions, dispersal would be disadvantageous; heat is lost more rapidly through wings in colder climates. The [[Larviform female|females]] of certain insect groups become sexually mature without metamorphosis, and some do not develop wings. Flightlessness in some female insects has been linked to higher [[fecundity]].<ref name="Barbosa, P. 1989" /> [[Aphid]]s are an example of insects which may never develop wings, depending on their environment. If resources are abundant on a host plant, there is no need to grow wings and disperse. If resources become diminished, their offspring may develop wings to disperse to other host plants.<ref name="Harrison1980" />


Two environments which favor neoteny are high altitudes and cool temperatures, because neotenous individuals have more fitness than individuals which metamorphose into an adult form. The energy required for metamorphosis detracts from individual fitness, and neotenous individuals can utilize available resources more easily.<ref name="Snyder, R. 1956">{{cite journal | last1=Snyder | first1=R | year=1956 | title=Comparative Features of the Life Histories of ''Ambystoma gracile'' (Baird) from Populations at Low and High Altitudes | journal=Copeia | volume=1956 | issue=1| pages=41–50 | jstor=1439242 | doi=10.2307/1439242}}</ref> This trend is seen in a comparison of salamander species at lower and higher altitudes; in a cool, high-altitude environment, neotenous individuals survive more and are more fecund than those which metamorphose into adult form.<ref name="Snyder, R. 1956" /> Insects in cooler environments tend to exhibit neoteny in flight because wings have a high surface area and lose heat quickly; it is disadvantageous for insects to metamorphose into adults.<ref name="Barbosa, P. 1989" />
Two environments which favor neoteny are high altitudes and cool temperatures, because neotenous individuals have more fitness than individuals which metamorphose into an adult form. The energy required for metamorphosis detracts from individual fitness, and neotenous individuals can utilize available resources more easily.<ref name="Snyder, R. 1956">{{cite journal |last=Snyder |first=R. |year=1956 |title=Comparative Features of the Life Histories of ''Ambystoma gracile'' (Baird) from Populations at Low and High Altitudes |journal=Copeia |volume=1956 |issue=1|pages=41–50 |jstor=1439242 |doi=10.2307/1439242}}</ref> This trend is seen in a comparison of salamander species at lower and higher altitudes; in a cool, high-altitude environment, neotenous individuals survive more and are more fecund than those which metamorphose into adult form.<ref name="Snyder, R. 1956" /> Insects in cooler environments tend to exhibit neoteny in flight because wings have a high surface area and lose heat quickly; it is disadvantageous for insects to metamorphose into adults.<ref name="Barbosa, P. 1989" />


Many species of salamander, and amphibians in general, exhibit environmental neoteny. [[Axolotl]] and [[olm]] are [[perennibranchiate]] salamander species which retain their juvenile aquatic form throughout adulthood, examples of full neoteny. Gills are a common juvenile characteristic in amphibians which are kept after maturation; examples are the tiger salamander and rough-skinned newt, both of which retain gills into adulthood.<ref name="Swingle, W. 1922 pp.397-421" />
Many species of salamander, and amphibians in general, exhibit environmental neoteny. [[Axolotl]] and [[olm]] are [[perennibranchiate]] salamander species which retain their juvenile aquatic form throughout adulthood, examples of full neoteny. Gills are a common juvenile characteristic in amphibians which are kept after maturation; examples are the tiger salamander and rough-skinned newt, both of which retain gills into adulthood.<ref name="Swingle, W. 1922 pp.397-421" />


[[Bonobo]]s share many physical characteristics with humans, including neotenous skulls.<ref name="ReferenceA">{{cite journal | last1=Shea | first1=B. T. | year=1983 | title=Paedomorphosis and Neoteny in the Pygmy Chimpanzee | journal=Science | volume=222 | issue=4623| pages=521–522 | jstor=1691380 | doi=10.1126/science.6623093 | pmid=6623093| bibcode=1983Sci...222..521S }}</ref> The shape of their skull does not change into adulthood (only increasing in size), due to [[sexual dimorphism]] and an evolutionary change in the timing of development.<ref name="ReferenceA" /> Juveniles became sexually mature before their bodies had fully developed as adults and, due to a selective advantage, the skull's neotenic structure remained.{{cn|date=January 2021}}
[[Bonobo]]s share many physical characteristics with humans, including neotenous skulls.<ref name="ReferenceA">{{cite journal |last1=Shea |first1=B. T. |year=1983 |title=Paedomorphosis and Neoteny in the Pygmy Chimpanzee |journal=Science |volume=222 |issue=4623 |pages=521–522 |jstor=1691380 |doi=10.1126/science.6623093 |pmid=6623093 |bibcode=1983Sci...222..521S }}</ref> The shape of their skull does not change into adulthood (only increasing in size), due to [[sexual dimorphism]] and an evolutionary change in the timing of development.<ref name="ReferenceA" />


In some groups, such as the insect families [[Gerridae]], [[Delphacidae]] and [[Ground beetle|Carabidae]], energy costs result in neoteny; many species in these families have [[brachyptery|small]], neotenous wings or [[aptery|none at all]].<ref name="Harrison1980">{{cite journal | last1=Harrison | first1=R | year=1980 | title=Dispersal polymorphisms in insects | journal=Annual Review of Ecology and Systematics | volume=11 | pages=95–118 | jstor=2096904 | doi=10.1146/annurev.es.11.110180.000523}}</ref> Some cricket species shed their wings in adulthood;<ref name="jstor.org">{{cite journal | last1=Harrison | first1=R | year=1980 | title=Dispersal Polymorphisms in Insects | journal=Annual Review of Ecology and Systematics | volume=11 | pages=95–118 | jstor=2096904 | doi=10.1146/annurev.es.11.110180.000523}}</ref> in the genus ''[[Ozopemon]]'', males (thought to be the first example of neoteny in [[beetle]]s) are significantly smaller than females due to [[inbreeding]].<ref>{{cite journal | last1=Jordal | first1=B. H. | last2=Beaver | first2=R. A. | last3=Normark | first3=B. B. | last4=Farrell | first4=B. D. | year=2002 | title=Extraordinary sex ratios and the evolution of male neoteny in sib-mating ''Ozopemon'' beetles | journal=Biological Journal of the Linnean Society | volume=75 | issue=3| pages=353–360 | doi=10.1046/j.1095-8312.2002.00025.x | doi-access=free }}</ref> In the termite ''[[Kalotermes flavicollis]]'', neoteny is seen in molting females.<ref name="dx.doi.org">{{cite journal | last1=Soltani-Mazouni | first1=N. | last2=Bordereau | first2=C. | year=1987 | title=Changes in the cuticle, ovaries and colleterial glands during the pseudergate and neotenic molt in ''Kalotermes flavicollis'' (FABR.) (Isoptera : Kalotermitidae) | journal=International Journal of Insect Morphology and Embryology | volume=16 | issue=3–4| pages=221–225 | doi=10.1016/0020-7322(87)90022-5 }}</ref>
In some groups, such as the insect families [[Gerridae]], [[Delphacidae]] and [[Ground beetle|Carabidae]], energy costs result in neoteny; many species in these families have [[brachyptery|small]], neotenous wings or [[aptery|none at all]].<ref name="Harrison1980">{{cite journal |last1=Harrison |first1=R. |year=1980 |title=Dispersal polymorphisms in insects |journal=Annual Review of Ecology and Systematics |volume=11 |pages=95–118 |jstor=2096904 |doi=10.1146/annurev.es.11.110180.000523}}</ref> Some cricket species shed their wings in adulthood;<ref name="jstor.org">{{cite journal |last1=Harrison |first1=R. |year=1980 |title=Dispersal Polymorphisms in Insects |journal=Annual Review of Ecology and Systematics |volume=11 |pages=95–118 |jstor=2096904 |doi=10.1146/annurev.es.11.110180.000523}}</ref> in the genus ''[[Ozopemon]]'', males (thought to be the first example of neoteny in [[beetle]]s) are significantly smaller than females due to [[inbreeding]].<ref>{{cite journal |last1=Jordal |first1=B. H. |last2=Beaver |first2=R. A. |last3=Normark |first3=B. B. |last4=Farrell |first4=B. D. |year=2002 |title=Extraordinary sex ratios and the evolution of male neoteny in sib-mating ''Ozopemon'' beetles |journal=Biological Journal of the Linnean Society |volume=75 |issue=3|pages=353–360 |doi=10.1046/j.1095-8312.2002.00025.x |doi-access=free }}</ref> In the termite ''[[Kalotermes flavicollis]]'', neoteny is seen in molting females.<ref name="dx.doi.org">{{cite journal |last1=Soltani-Mazouni |first1=N. |last2=Bordereau |first2=C. |year=1987 |title=Changes in the cuticle, ovaries and colleterial glands during the pseudergate and neotenic molt in ''Kalotermes flavicollis'' (FABR.) (Isoptera : Kalotermitidae) |journal=International Journal of Insect Morphology and Embryology |volume=16 |issue=3–4|pages=221–225 |doi=10.1016/0020-7322(87)90022-5 }}</ref>


In other species, such as the [[northwestern salamander]] (''Ambystoma gracile''), environmental conditions{{snd}}high altitude, in this case{{snd}}cause neoteny.<ref>{{cite journal | last1=Eagleson | first1=G. | last2=McKeown | first2=B. | year=1978 | title=Changes in thyroid activity of ''Ambystoma gracile'' (Baird) during different larval, transforming, and postmetamorphic phases | journal=Canadian Journal of Zoology | volume=56 | issue=6| pages=1377–1381 | doi= 10.1139/z78-190}}</ref> Neoteny is also found in a few species of the crustacean family [[Asellota#Classification|Ischnomesidae]], which live in deep ocean water.<ref>{{cite journal | last1=Brokeland | first1=W. | last2=Brandt | first2=A. | year=2004 | title=Two new species of Ischnomesidae (Crustacea: Isopoda) from the Southern Ocean displaying neoteny | journal=Deep-Sea Research Part II | volume=51 | issue=14–16| pages=1769–1785 | doi=10.1016/j.dsr2.2004.06.034 | bibcode=2004DSRII..51.1769B }}</ref>
In other species, such as the [[northwestern salamander]] (''Ambystoma gracile''), environmental conditions{{snd}}high altitude, in this case{{snd}}cause neoteny.<ref>{{cite journal |last1=Eagleson |first1=G. |last2=McKeown |first2=B. |year=1978 |title=Changes in thyroid activity of ''Ambystoma gracile'' (Baird) during different larval, transforming, and postmetamorphic phases |journal=Canadian Journal of Zoology |volume=56 |issue=6|pages=1377–1381 |doi= 10.1139/z78-190}}</ref> Neoteny is also found in a few species of the crustacean family [[Asellota#Classification|Ischnomesidae]], which live in deep ocean water.<ref>{{cite journal |last1=Brokeland |first1=W. |last2=Brandt |first2=A. |year=2004 |title=Two new species of Ischnomesidae (Crustacea: Isopoda) from the Southern Ocean displaying neoteny |journal=Deep-Sea Research Part II |volume=51 |issue=14–16|pages=1769–1785 |doi=10.1016/j.dsr2.2004.06.034 |bibcode=2004DSRII..51.1769B }}</ref>

Neoteny is an ancient, pervasive phenomenon. In [[urodeles]], many extant taxa are neotenic,<ref name="Wiens et al. 2005">{{cite journal |last1=Wiens |first1=John J. |last2=Bonett |first2=Ronald M. |last3=Chippindale |first3=Paul T. |last4=Anderson |first4=Frank (Andy) |title=Ontogeny Discombobulates Phylogeny: Paedomorphosis and Higher-Level Salamander Relationships |journal=Systematic Biology |date=1 February 2005 |volume=54 |issue=1 |pages=91–110 |doi=10.1080/10635150590906037 |pmid=15805013 |url=https://doi.org/10.1080/10635150590906037}}</ref> and both morphological <ref name="Evans et al. 1988">{{cite journal |last1=Evans |first1=Susan E. |last2=Milner |first2=Andrew R. |last3=Mussett |first3=Frances |title=The earliest known Salamanders (Amphibia, Caudata):A record from the Middle Jurassic of England |journal=Geobios |date=1 January 1988 |volume=21 |issue=5 |pages=539–552 |doi=10.1016/S0016-6995(88)80069-X |bibcode=1988Geobi..21..539E |url=https://doi.org/10.1016/S0016-6995(88)80069-X |issn=0016-6995}}</ref> and histological data suggest that the Middle [[Jurassic]] taxon ''[[Marmorerpeton]]'' was neotenic.<ref name="de Buffrénil et al. 2015">{{cite journal |last1=de Buffrénil |first1=Vivian |last2=Canoville |first2=Aurore |last3=Evans |first3=Susan E. |last4=Laurin |first4=Michel |title=Histological study of karaurids, the oldest known (stem) urodeles |journal=Historical Biology |date=2 January 2015 |volume=27 |issue=1 |pages=109–114 |doi=10.1080/08912963.2013.869800 |bibcode=2015HBio...27..109D |url=http://dx.doi.org/10.1080/08912963.2013.869800}}</ref>


== Subcellular neoteny ==
== Subcellular neoteny ==


Neoteny is usually used to describe animal development; however, neoteny is also seen in the cell [[organelles]]. It was suggested that subcellular neoteny could explain why [[sperm cells]] have atypical [[centrioles]]. One of the two sperm centrioles of [[Drosophilidae|fruit fly]] exhibit the retention of "juvenile" centriole structure, which can be described as centriolar "neoteny". This neotenic, atypical centriole is known as the [[Proximal Centriole-Like]]. Typical centrioles form via a step by step process in which a cartwheel forms, then develops to become a procentriole, and further matures into a centriole. The neotenic centriole of fruit fly resembles an early procentriole.<ref>{{Citation |last1=Avidor-Reiss |first1=Tomer |title=The Evolution of Centriole Structure: Heterochrony, Neoteny, and Hypermorphosis |date=2019 |url=https://doi.org/10.1007/978-3-030-23173-6_1 |work=The Golgi Apparatus and Centriole: Functions, Interactions and Role in Disease |pages=3–15 |editor-last=Kloc |editor-first=Malgorzata |access-date=2023-10-12 |series=Results and Problems in Cell Differentiation |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-030-23173-6_1 |isbn=978-3-030-23173-6 |pmc=7576685 |pmid=31435789 |last2=Turner |first2=Katerina|volume=67 }}</ref>
Neoteny is usually used to describe animal development; however, neoteny is also seen in the cell [[organelles]]. It was suggested that subcellular neoteny could explain why [[sperm cells]] have atypical [[centrioles]]. One of the two sperm centrioles of [[Drosophilidae|fruit fly]] exhibit the retention of "juvenile" centriole structure, which can be described as centriolar "neoteny". This neotenic, atypical centriole is known as the [[Proximal Centriole-Like]]. Typical centrioles form via a step by step process in which a cartwheel forms, then develops to become a procentriole, and further matures into a centriole. The neotenic centriole of fruit fly resembles an early procentriole.<ref>{{Citation |last1=Avidor-Reiss |first1=Tomer |last2=Turner |first2=Katerina |title=The Evolution of Centriole Structure: Heterochrony, Neoteny, and Hypermorphosis |date=2019 |url=https://doi.org/10.1007/978-3-030-23173-6_1 |work=The Golgi Apparatus and Centriole: Functions, Interactions and Role in Disease |pages=3–15 |editor-last=Kloc |editor-first=Malgorzata |access-date=12 October 2023 |series=Results and Problems in Cell Differentiation |place=Cham |publisher=Springer International |doi=10.1007/978-3-030-23173-6_1 |isbn=978-3-030-23173-6 |pmc=7576685 |pmid=31435789 |volume=67 }}</ref>


== See also ==
== See also ==
Line 62: Line 65:
* [[Larviform female]]
* [[Larviform female]]
* [[Moe (slang)]]
* [[Moe (slang)]]
* [[Neotenic complex syndrome]]
* [[Neotenin]]
* [[Neotenin]]


Line 70: Line 74:


* Bergstorm, Carl T. & Dugatkin, Lee Alan (2012). ''Evolution'', W.W. Norton {{ISBN|039391349X}}
* Bergstorm, Carl T. & Dugatkin, Lee Alan (2012). ''Evolution'', W.W. Norton {{ISBN|039391349X}}

== External links ==

* {{Cite web|last=Singer|first=Emily|date=2015-06-02|title=How Dinosaurs Shrank and Became Birds|url=https://www.quantamagazine.org/how-birds-evolved-from-dinosaurs-20150602/|website=[[Quanta Magazine]]}}


{{genarch}}
{{genarch}}

Latest revision as of 20:58, 9 December 2024

"Paedogenesis" redirects here. For the topic of soil formation, see Pedogenesis.

Neoteny (/niˈɒtəni/),[1][2][3][4] also called juvenilization,[5] is the delaying or slowing of the physiological, or somatic, development of an organism, typically an animal. Neoteny in modern humans is more significant than in other primates.[6] In progenesis or paedogenesis, sexual development is accelerated.[7]

Both neoteny and progenesis result in paedomorphism[8] (as having the form typical of children) or paedomorphosis[9] (changing towards forms typical of children), a type of heterochrony.[10] It is the retention in adults of traits previously seen only in the young. Such retention is important in evolutionary biology, domestication, and evolutionary developmental biology. Some authors define paedomorphism as the retention of larval traits, as seen in salamanders.[11][12][13]

History and etymology

[edit]
Diagram of the six types of shift in heterochrony, a change in the timing or rate of any process in embryonic development. Predisplacement, hypermorphosis, and acceleration (red) extend development (peramorphosis); postdisplacement, hypomorphosis, and deceleration (blue) all truncate it (paedomorphosis).

Julius Kollmann created the term "neoteny" in 1885 after he described the axolotl's maturation while remaining in a tadpole-like aquatic stage complete with gills, unlike other adult amphibians like frogs and toads.[14][15]

The word neoteny is borrowed from the German Neotenie, the latter constructed by Kollmann from the Greek νέος (neos, "young") and τείνειν (teínein, "to stretch, to extend"). The adjective is either "neotenic" or "neotenous".[16] For the opposite of "neotenic", different authorities use either "gerontomorphic"[17][18] or "peramorphic".[19] Bogin points out that Kollmann had intended the meaning to be "retaining youth", but had evidently confused the Greek teínein with the Latin tenere, which had the meaning he wanted, "to retain", so that the new word would mean "the retaining of youth (into adulthood)".[15]

In 1926, Louis Bolk described neoteny as the major process in humanization.[20][15] In his 1977 book Ontogeny and Phylogeny,[21] Stephen Jay Gould noted that Bolk's account constituted an attempted justification for "scientific" racism and sexism, but acknowledged that Bolk had been right in the core idea that humans differ from other primates in becoming sexually mature in an infantile stage of body development.[15]

In humans

[edit]
Main article: Neoteny in humans

Neoteny in humans is the slowing or delaying of body development, compared to non-human primates, resulting in features such as a large head, a flat face, and relatively short arms. These neotenic changes may have been brought about by sexual selection in human evolution. In turn, they may have permitted the development of human capacities such as emotional communication. Some evolutionary theorists have proposed that neoteny was a key feature in human evolution.[22] J. B. S. Haldane states a "major evolutionary trend in human beings" is "greater prolongation of childhood and retardation of maturity."[5] Delbert D. Thiessen said that "neoteny becomes more apparent as early primates evolved into later forms" and that primates have been "evolving toward flat face."[23] Doug Jones argued that human evolution's trend toward neoteny may have been caused by sexual selection in human evolution for neotenous facial traits in women by men with the resulting neoteny in male faces being a "by-product" of sexual selection for neotenous female faces.[24]

In domestic animals

[edit]
Further information: Domestication of animals

Neoteny is seen in domesticated animals such as dogs and mice.[25] This is because there are more resources available, less competition for those resources, and with the lowered competition the animals expend less energy obtaining those resources. This allows them to mature and reproduce more quickly than their wild counterparts.[25] The environment that domesticated animals are raised in determines whether or not neoteny is present in those animals. Evolutionary neoteny can arise in a species when those conditions occur, and a species becomes sexually mature ahead of its "normal development". Another explanation for the neoteny in domesticated animals can be the selection for certain behavioral characteristics. Behavior is linked to genetics which therefore means that when a behavioral trait is selected for, a physical trait may also be selected for due to mechanisms like linkage disequilibrium. Often, juvenile behaviors are selected for in order to more easily domesticate a species; aggressiveness in certain species comes with adulthood when there is a need to compete for resources. If there is no need for competition, then there is no need for aggression. Selecting for juvenile behavioral characteristics can lead to neoteny in physical characteristics because, for example, with the reduced need for behaviors like aggression, there is no need for developed traits that would help in that area. Traits that may become neotenized due to decreased aggression may be a shorter muzzle and smaller general size among the domesticated individuals. Some common neotenous physical traits in domesticated animals (mainly rabbits, dogs, pigs, ferrets, cats, and even foxes) include floppy ears, changes in the reproductive cycle, curly tails, piebald coloration, fewer or shortened vertebra, large eyes, rounded forehead, large ears, and shortened muzzle.[26][27][28]

Neoteny and reduction in skull size – grey wolf and chihuahua skulls

When the role of dogs expanded from just being working dogs to also being companions, humans started selective breeding dogs for morphological neoteny, and this selective breeding for "neoteny or paedomorphism" "strengthened the human-canine bond."[29] Humans bred dogs to have more "juvenile physical traits" as adults, such as short snouts and wide-set eyes which are associated with puppies because people usually consider these traits to be more attractive. Some breeds of dogs with short snouts and broad heads such as the Komondor, Saint Bernard and Maremma Sheepdog are more morphologically neotenous than other breeds of dogs.[30] Cavalier King Charles spaniels are an example of selection for neoteny because they exhibit large eyes, pendant-shaped ears and compact feet, giving them a morphology similar to puppies as adults.[29]

In 2004, a study that used 310 wolf skulls and over 700 dog skulls representing 100 breeds concluded that the evolution of dog skulls can generally not be described by heterochronic processes such as neoteny, although some pedomorphic dog breeds have skulls that resemble the skulls of juvenile wolves.[31] By 2011, the findings by the same researcher were simply "Dogs are not paedomorphic wolves."[32]

In other species

[edit]
A green salamander with four short legs
The axolotl is a neotenous salamander, often retaining gills throughout its life.

Neoteny has been observed in many other species. It is important to note the difference between partial and full neoteny when looking at other species, to distinguish between juvenile traits which are advantageous in the short term and traits which are beneficial throughout the organism's life; this might provide insight into the cause of neoteny in a species. Partial neoteny is the retention of the larval form beyond the usual age of maturation, with possible sexual development (progenesis) and eventual maturation into the adult form; this is seen in the frog Lithobates clamitans. Full neoteny is seen in Ambystoma mexicanum and some populations of Ambystoma tigrinum, which remain in larval form throughout their lives.[33][34] Lithobates clamitans is partially neotenous; it delays maturation during the winter as fewer resources are available; it can find resources more easily in its larval form. This encompasses both of the main causes of neoteny; the energy required to survive in the winter as a newly-formed adult is too great, so the organism exhibits neotenous characteristics until it can better survive as an adult. Ambystoma tigrinum retains its neoteny for a similar reason; however, the retention is permanent due to the lack of available resources throughout its lifetime. This is another example of an environmental cause of neoteny. Several avian species, such as the manakins Chiroxiphia linearis and Chiroxiphia caudata, exhibit partial neoteny. The males of both species retain juvenile plumage into adulthood, losing it when they are fully mature.[35]

Neoteny is commonly seen in flightless insects, such as the females of the order Strepsiptera. Flightlessness in insects has evolved separately a number of times; factors which may have contributed to the separate evolution of flightlessness are high altitude, geographic isolation (islands), and low temperatures.[36] Under these environmental conditions, dispersal would be disadvantageous; heat is lost more rapidly through wings in colder climates. The females of certain insect groups become sexually mature without metamorphosis, and some do not develop wings. Flightlessness in some female insects has been linked to higher fecundity.[36] Aphids are an example of insects which may never develop wings, depending on their environment. If resources are abundant on a host plant, there is no need to grow wings and disperse. If resources become diminished, their offspring may develop wings to disperse to other host plants.[37]

Two environments which favor neoteny are high altitudes and cool temperatures, because neotenous individuals have more fitness than individuals which metamorphose into an adult form. The energy required for metamorphosis detracts from individual fitness, and neotenous individuals can utilize available resources more easily.[38] This trend is seen in a comparison of salamander species at lower and higher altitudes; in a cool, high-altitude environment, neotenous individuals survive more and are more fecund than those which metamorphose into adult form.[38] Insects in cooler environments tend to exhibit neoteny in flight because wings have a high surface area and lose heat quickly; it is disadvantageous for insects to metamorphose into adults.[36]

Many species of salamander, and amphibians in general, exhibit environmental neoteny. Axolotl and olm are perennibranchiate salamander species which retain their juvenile aquatic form throughout adulthood, examples of full neoteny. Gills are a common juvenile characteristic in amphibians which are kept after maturation; examples are the tiger salamander and rough-skinned newt, both of which retain gills into adulthood.[33]

Bonobos share many physical characteristics with humans, including neotenous skulls.[39] The shape of their skull does not change into adulthood (only increasing in size), due to sexual dimorphism and an evolutionary change in the timing of development.[39]

In some groups, such as the insect families Gerridae, Delphacidae and Carabidae, energy costs result in neoteny; many species in these families have small, neotenous wings or none at all.[37] Some cricket species shed their wings in adulthood;[40] in the genus Ozopemon, males (thought to be the first example of neoteny in beetles) are significantly smaller than females due to inbreeding.[41] In the termite Kalotermes flavicollis, neoteny is seen in molting females.[42]

In other species, such as the northwestern salamander (Ambystoma gracile), environmental conditions – high altitude, in this case – cause neoteny.[43] Neoteny is also found in a few species of the crustacean family Ischnomesidae, which live in deep ocean water.[44]

Neoteny is an ancient, pervasive phenomenon. In urodeles, many extant taxa are neotenic,[45] and both morphological [46] and histological data suggest that the Middle Jurassic taxon Marmorerpeton was neotenic.[47]

Subcellular neoteny

[edit]

Neoteny is usually used to describe animal development; however, neoteny is also seen in the cell organelles. It was suggested that subcellular neoteny could explain why sperm cells have atypical centrioles. One of the two sperm centrioles of fruit fly exhibit the retention of "juvenile" centriole structure, which can be described as centriolar "neoteny". This neotenic, atypical centriole is known as the Proximal Centriole-Like. Typical centrioles form via a step by step process in which a cartwheel forms, then develops to become a procentriole, and further matures into a centriole. The neotenic centriole of fruit fly resembles an early procentriole.[48]

See also

[edit]

References

[edit]
  1. ^ "neoteny". Dictionary.com Unabridged (Online). n.d. Retrieved 21 April 2019.
  2. ^ "neoteny". The American Heritage Dictionary of the English Language (5th ed.). HarperCollins. Retrieved 21 April 2019.
  3. ^ "neoteny". Lexico US English Dictionary. Oxford University Press. Archived from the original on 22 March 2020.
  4. ^ "neoteny". Merriam-Webster.com Dictionary. Merriam-Webster. Retrieved 21 April 2019.
  5. ^ a b Montagu, A. (1989). Growing Young. Bergin & Garvey: CT.
  6. ^ Choi, Charles Q. (1 July 2009). "Being More Infantile May Have Led to Bigger Brains". Scientific American.
  7. ^ Volkenstein, M. V. 1994. Physical Approaches to Biological Evolution. Springer-Verlag: Berlin, [1].
  8. ^ "Paedomorphic". 21 January 2022.
  9. ^ "Morphosis". 6 June 2022.
  10. ^ Ridley, Mark (1985). Evolution. Blackwell.
  11. ^ Whiteman, H.H. (1994). "Evolution of facultative paedomorphosis". Quarterly Review of Biology. 69 (2): 205–221. doi:10.1086/418540. S2CID 83500486.
  12. ^ Schell, S. C. Handbook of Trematodes of North America North of Mexico, 1985, pg. 22
  13. ^ Ginetsinskaya, T.A. Trematodes, Their Life Cycles, Biology and Evolution. Leningrad, USSR: Nauka 1968. Translated in 1988, [2].
  14. ^ Kollmann, J. (1885). "Das Ueberwintern von europäischen Frosch- und Tritonlarven und die Umwandlung des mexikanischen Axolotl" [The overwintering of European frog- and triton larvae and the transformation of the Mexican axolotl]. Verhandlungen der Naturforschenden Gesellschaft in Basel (Proceedings of the Natural Science Society of Basel) (in German). 7: 387–398. From pp. 397–398: "Dann drängt sich die Frage auf, ob das Latenzstadium der Eier, das einerseits bei Fischen, Vögeln and Säugethieren in so höchst überraschenden Formen vorkommt, anderseits das Latenzstadium bei den Wirbellosen ¹) nicht eine Variante derselben Eigenschaft der Organismen sei, welche ich Neotenie genannt habe, und die auf irgend einer Entwichlungsstufe in Kraft treten kann." (Then the question arises whether on the one hand the latency stage of eggs — which occurs in such highly surprising forms in fish, birds and mammals — [and] on the other hand the latency stage in invertebrates ¹) be not a variant of the same property of the organisms, which I have called "neoteny" and which can come into force at any stage of development.)
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  38. ^ a b Snyder, R. (1956). "Comparative Features of the Life Histories of Ambystoma gracile (Baird) from Populations at Low and High Altitudes". Copeia. 1956 (1): 41–50. doi:10.2307/1439242. JSTOR 1439242.
  39. ^ a b Shea, B. T. (1983). "Paedomorphosis and Neoteny in the Pygmy Chimpanzee". Science. 222 (4623): 521–522. Bibcode:1983Sci...222..521S. doi:10.1126/science.6623093. JSTOR 1691380. PMID 6623093.
  40. ^ Harrison, R. (1980). "Dispersal Polymorphisms in Insects". Annual Review of Ecology and Systematics. 11: 95–118. doi:10.1146/annurev.es.11.110180.000523. JSTOR 2096904.
  41. ^ Jordal, B. H.; Beaver, R. A.; Normark, B. B.; Farrell, B. D. (2002). "Extraordinary sex ratios and the evolution of male neoteny in sib-mating Ozopemon beetles". Biological Journal of the Linnean Society. 75 (3): 353–360. doi:10.1046/j.1095-8312.2002.00025.x.
  42. ^ Soltani-Mazouni, N.; Bordereau, C. (1987). "Changes in the cuticle, ovaries and colleterial glands during the pseudergate and neotenic molt in Kalotermes flavicollis (FABR.) (Isoptera : Kalotermitidae)". International Journal of Insect Morphology and Embryology. 16 (3–4): 221–225. doi:10.1016/0020-7322(87)90022-5.
  43. ^ Eagleson, G.; McKeown, B. (1978). "Changes in thyroid activity of Ambystoma gracile (Baird) during different larval, transforming, and postmetamorphic phases". Canadian Journal of Zoology. 56 (6): 1377–1381. doi:10.1139/z78-190.
  44. ^ Brokeland, W.; Brandt, A. (2004). "Two new species of Ischnomesidae (Crustacea: Isopoda) from the Southern Ocean displaying neoteny". Deep-Sea Research Part II. 51 (14–16): 1769–1785. Bibcode:2004DSRII..51.1769B. doi:10.1016/j.dsr2.2004.06.034.
  45. ^ Wiens, John J.; Bonett, Ronald M.; Chippindale, Paul T.; Anderson, Frank (Andy) (1 February 2005). "Ontogeny Discombobulates Phylogeny: Paedomorphosis and Higher-Level Salamander Relationships". Systematic Biology. 54 (1): 91–110. doi:10.1080/10635150590906037. PMID 15805013.
  46. ^ Evans, Susan E.; Milner, Andrew R.; Mussett, Frances (1 January 1988). "The earliest known Salamanders (Amphibia, Caudata):A record from the Middle Jurassic of England". Geobios. 21 (5): 539–552. Bibcode:1988Geobi..21..539E. doi:10.1016/S0016-6995(88)80069-X. ISSN 0016-6995.
  47. ^ de Buffrénil, Vivian; Canoville, Aurore; Evans, Susan E.; Laurin, Michel (2 January 2015). "Histological study of karaurids, the oldest known (stem) urodeles". Historical Biology. 27 (1): 109–114. Bibcode:2015HBio...27..109D. doi:10.1080/08912963.2013.869800.
  48. ^ Avidor-Reiss, Tomer; Turner, Katerina (2019), Kloc, Malgorzata (ed.), "The Evolution of Centriole Structure: Heterochrony, Neoteny, and Hypermorphosis", The Golgi Apparatus and Centriole: Functions, Interactions and Role in Disease, Results and Problems in Cell Differentiation, vol. 67, Cham: Springer International, pp. 3–15, doi:10.1007/978-3-030-23173-6_1, ISBN 978-3-030-23173-6, PMC 7576685, PMID 31435789, retrieved 12 October 2023

Further reading

[edit]
  • Bergstorm, Carl T. & Dugatkin, Lee Alan (2012). Evolution, W.W. Norton ISBN 039391349X
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