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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

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

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

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]

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

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

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]

References

^ "neoteny". Dictionary.com Unabridged (Online). n.d. Retrieved 21 April 2019.
^ "neoteny". The American Heritage Dictionary of the English Language (5th ed.). HarperCollins. Retrieved 21 April 2019.
^ "neoteny". Lexico US English Dictionary. Oxford University Press. Archived from the original on 22 March 2020.
^ "neoteny". Merriam-Webster.com Dictionary. Merriam-Webster. Retrieved 21 April 2019.
^ ^a ^b Montagu, A. (1989). Growing Young. Bergin & Garvey: CT.
^ Choi, Charles Q. (1 July 2009). "Being More Infantile May Have Led to Bigger Brains". Scientific American.
^ Volkenstein, M. V. 1994. Physical Approaches to Biological Evolution. Springer-Verlag: Berlin, [1].
^ "Paedomorphic". 21 January 2022.
^ "Morphosis". 6 June 2022.
^ Ridley, Mark (1985). Evolution. Blackwell.
^ Whiteman, H.H. (1994). "Evolution of facultative paedomorphosis". Quarterly Review of Biology. 69 (2): 205–221. doi:10.1086/418540. S2CID 83500486.
^ Schell, S. C. Handbook of Trematodes of North America North of Mexico, 1985, pg. 22
^ Ginetsinskaya, T.A. Trematodes, Their Life Cycles, Biology and Evolution. Leningrad, USSR: Nauka 1968. Translated in 1988, [2].
^ 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.)
^ ^a ^b ^c ^d Bogin, Barry (1999). Patterns of Human Growth. Cambridge University Press. pp. 157–169. ISBN 978-0-521-56438-0.
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^ ^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.
^ ^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.
^ Harrison, R. (1980). "Dispersal Polymorphisms in Insects". Annual Review of Ecology and Systematics. 11: 95–118. Bibcode:1980AnRES..11...95H. doi:10.1146/annurev.es.11.110180.000523. JSTOR 2096904.
^ 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.
^ 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.
^ 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. Bibcode:1978CaJZ...56.1377E. doi:10.1139/z78-190.
^ 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.
^ 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.
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^ 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

@@ Line 1: / Line 1: @@
+{{Short description|Retaining juvenile features into adulthood}}
-{{for|the topic of soil formation|Pedogenesis}}
-[[File:Neoteny body proportion heterochrony human.png|thumb|300px|Human [[body proportion]] changes with age]]
-[[Image:Pomeranian orange-sable Coco.jpg|thumb|250px|[[Toy dog]]s often display an extreme level of neoteny, resembling not just infant, but [[fetal]] wolves<ref> {{cite book |title=The Covenant of the Wild: Why animals chose domestication |last=Budiansky |first=Stephen |year=1999 |publisher=Yale University Press |isbn=0300079931}}</ref>]]
-'''Neoteny''' ({{IPAc-en|icon|n|iː|ˈ|ɒ|t|ɨ|n|iː}}), also called '''juvenilization''',<ref name="Montagu">Montagu, A. (1989). Growing Young. Bergin & Garvey: CT.</ref> is one of the two ways by which pedomorphism can arise. Pedomorphism is the retention by adults of traits previously seen only in juveniles, and is a subject studied in the field of [[developmental biology]]. In neoteny, the [[Physiology|physiological]] (or [[somatic]]) development of an animal or organism is slowed or delayed. In contrast, in progenesis, sexual development occurs faster. Both processes result in pedomorphism.<ref name="Ridley">Ridley, Mark. [http://www.blackwellpublishing.com/ridley/a-z/Neoteny.asp "Neoteny"], ''Evolution'', Blackwell Publishing, 1985.</ref> Ultimately this process results in the retention, in the adults of a [[species]], of juvenile physical characteristics well into maturity and '''pedogenesis''' ('''paedogenesis'''), the reproduction in a neotenized state.<ref name="Schell">Schell, S. C. ''Handbook of Trematodes of North America North of Mexico'', 1985, pg. 22</ref>
+{{redirect|Paedogenesis|the topic of soil formation|Pedogenesis}}
-Neoteny is one of three dimensions of [[heterochrony]], or the change in timing of developmental events: acceleration (faster) vs. neoteny (slower), hypermorphosis (further) vs. progenesis (not as far), and predisplacement (begins earlier) vs. postdisplacement (begins later).<ref>Rice, S. H. [http://bi154.dhcp.ttu.edu/sean/hetero.html "Heterochrony"]. November 2007. Accessed July 14, 2011. </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>
-The  word ''neoteny'' is borrowed from the [[German language|German]] ''Neotenie'', the latter constructed from the [[Greek language|Greek]] ''νέος'' (''neos'', young) and ''τείνειν'' (''teínein'', tend to). The [[adjectival]] form of the word is either "neotenous" or "neotenic".<ref>[http://www.thefreedictionary.com/neotenous "Neotenous"], ''The Free Dictionary''. 2011. Accessed April 30, 2011.</ref> The opposite of neoteny is either called "'''gerontomorphic'''"<ref name="Henke" /> or '''"peramorphic"'''<ref name="Hall" />.
+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>
-==In humans==
-===Neotenous traits in humans===
-{{double image|right|Betty_Boop_patent_fig1.jpg|100|Betty_Boop_patent_fig2.jpg|100|Physical anthropologist [[Barry Bogin]] considers [[Betty Boop]] to be an example of neoteny<ref name="Bogin">Bogin, B. (1999). Patterns of Human Growth. Cambridge University Press, NY.</ref>}}
+== History and etymology ==
-These are neotenous traits in humans: flattened face,<ref name="Montagu" /> broadened face,<ref name="Ontogeny">Gould, S.J. (1977) Ontogeny and Phylogeny, Cambridge: Belknap Press.</ref> large brain,<ref name="Montagu" /> hairless body,<ref name="Montagu" /> hairless face,<ref name="Jean">Jean-Baptiste de Panafieu, P. (2007). Evolution. Seven Stories Press, USA.</ref> small nose,<ref name="Jean" /> reduction of brow ridge,<ref name="Montagu" /> small teeth,<ref name="Montagu" /> small upper jaw (maxilla),<ref name="Montagu" /> small lower jaw (mandible),<ref name="Montagu" /> thinness of skull bones,<ref name="Ontogeny" /> limbs proportionately short compared to torso length,<ref name="Ontogeny" /> longer leg than arm length,<ref>Smith, J.M. (1958). The theory of evolution. Cambridge University Press.</ref> larger eyes,<ref>http://zidbits.com/2011/06/why-do-men-find-women-with-larger-eyes-attractive/</ref> and upright stance.<ref name="Hether">Hetherington, R. (2010). The Climate Connection: Climate Change and Modern Human Evolution. Cambridge University Press.</ref><ref name="Henke">Henke, W. (2007). Handbook of paleoanthropology, Volume 1. Springer Books, NY.</ref>
+[[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).]]
-===Human evolution===
-{{main|human evolution}}
-Many prominent evolutionary theorists propose that neoteny has been a key feature in human evolution. [[Stephen Jay Gould]] believed that the "evolutionary story" of humans is one where we have been "retaining to adulthood the originally juvenile features of our ancestors".<ref name="Mickey">Gould, S.J. A Biological Homage to Mickey Mouse. </ref> J.B.S. Haldane mirrors Gould's hypothesis by stating a "major evolutionary trend in human beings" is "greater prolongation of childhood and retardation of maturity."<ref name="Montagu" /> [[Del Thiessen|Delbert D. Thiessen]] claimed 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> However, in light of some groups using arguments based around neoteny to support [[racism]], Gould also argued "that the whole enterprise of ranking groups by degree of neoteny is fundamentally unjustified" (Gould, 1996, pg. 150).<ref name="mismeasure" />
+[[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>
-[[Greenspan and Shanker]] have proposed a theory (in their book ''The First Idea'') of psychological development in which neoteny is seen as crucial for the "development of species-typical capacities" that depend upon a long period of attachment to caregivers for the opportunities to engage in and develop their capacity for emotional communication. Because of the importance of facial expression in the process of interactive signalling, neotenous features, such as hair loss, allow for more efficient and rapid communication of socially important messages that are based on facially expressive emotional signalling. (Shanker and Greenspan, 2004, p. 130)
-Other theorists have argued that neoteny has not been the main cause of human evolution, because humans only retain some juvenile traits, while relinquishing others.<ref name="Rantala" /> For example, the high leg-to-body ratio (long legs) of adult humans as opposed to human infants shows that there is not a holistic trend in humans towards neoteny when compared to the other [[great apes]].<ref name="Rantala">Rantala, M.J. (2006). Evolution of nakedness in Homo sapiens. In Zoology. </ref>  <ref name "Shea">Shea BT. 1989. Heterochrony in human evolution: the case for neoteny reconsidered. American Journal of Physical Anthropology 80: 69-101.</ref> Andrew Arthur Abbie agrees, citing the gerontomorphic fleshy human nose and long human legs as contradicting the neoteny hominid evolution hypothesis, although he does believe humans are generally neotenous.<ref name="Henke" /> [[Brian K. Hall]] also cites the long legs of humans as a [[Peramorphosis|peramorphic]] trait, which is in sharp contrast to neoteny.<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>
+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 |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" />
-On the balance, an all or nothing approach could be regarded as pointless, with a combination of [[Heterochrony|heterochronic]] processes being more likely and more reasonable (Vrba, 1996).
-===Between sexes===
+== In humans ==
+{{main|Neoteny in humans}}
-[[Ashley Montagu]] notes the following neotenous traits in women relative to men: more delicate skeleton, smoother ligament attachments, smaller mastoid processes, reduced [[brow ridge]]s, more forward tilt of the head, narrower joints, less hairy, more delicate skin, retention of [[Lanugo|fetal body hair]], smaller body size, more backward tilt of pelvis, greater longevity, lower basal metabolism, faster heartbeat, greater extension of development periods, higher pitched voice and larger tear ducts.<ref name="Montagu" />
+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>
-Note that [[Cro-Magnon]] humans (40,000 to 10,000 years ago) differed from co-existing [[Neanderthal]]ers in the following ways: "higher forehead, less prominent brow ridges, smaller teeth, less robust bodies, and reduced sexual dimorphism."<ref>Greenspan and Shanker. ''The First Idea'', 2004, p. 167.</ref>
+== In domestic animals ==
-====Attractive women's faces====
-{{worldview|section|date=January 2012}}
-{{onesource|section|date=January 2012}}
-{{main|physical attractiveness}}
-In a cross-cultural study, more neotenized female faces were the most attractive to men while less neotenized female faces were the least attractive to men, regardless of the females' actual age.<ref>Jones, D. ''Sexual Selection, Physical Attractiveness and Facial Neoteny: Cross-Cultural Evidence and Implications''. p.723.</ref> Using a panel of "[[Asian people|Asian]]", "[[Hispanic]]" and "[[White people|White]]" judges, Michael R. Cunningham found that the Asian, Hispanic and White female faces found most attractive were those that had "neonate large eyes, greater distance between eyes, and small noses"<ref name="Cunningham" /> and his study led him to conclude that "large eyes" were the most "effective" of the "neonate cues".<ref name="Cunningham" /> Cunningham also said that "shiny" hair may be indicative of "neonate vitality".<ref name="Cunningham" />
+{{further|Domestication of animals}}
-Cunningham noted a "difference" in the preferences of Asian and White judges with Asian judges preferring women with "less mature faces" and smaller mouths than the White judges.<ref name="Cunningham" /> Cunningham hypothesized that this difference in preference may stem from "ethnocentrism" since "Asian faces possess those qualities", so Cunningham re-analyzed the data with "11 Asian targets excluded" and concluded that "ethnocentrism was not a primary determinant of Asian preferences."<ref name="Cunningham" /> Using a panel of "[[Black people|Blacks]]" and "Whites" as judges, Cunningham found more neotenous faces were perceived as having both higher "femininity" and "sociability".<ref name="Cunningham" />
+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>
-In contrast, Cunningham found that faces that were "low in neoteny" were judged as "intimidating".<ref name="Cunningham" /> Upon analyzing the results of his study Cunningham concluded that preference for "neonate features may display the least cross-cultural variability" in terms of "attractiveness ratings".<ref name="Cunningham">Cunningham, M., Roberts, A., & Vu, C. (1995). "Their ideas of beauty are, on the whole, the same as ours": consistency and variability in the cross-cultural perception of female physical attractiveness. Journal of Personality and Social Psychology, 68, 261-79. {{doi|10.1037/0022-3514.68.2.261}}</ref> In a study of Italian women who have won beauty competitions, it was found these women had faces characterized by more "babyness" traits compared to the "normal" women used as a reference.<ref name="Chiarella">Chiarella Sforza, Alberto Laino, Raoul D'Alessio, Gaia Grandi, Miriam Binelli and Virgilio Ferruccio Ferrario (2009) Soft-Tissue Facial Characteristics of Attractive Italian Women as Compared to Normal Women. The Angle Orthodontist: January 2009, Vol. 79, No. 1, pp. 17-23.</ref> In a study of sixty Caucasian female faces, the average facial composite of the fifteen faces found most attractive differed from the facial composite of the whole by having a reduced lower facial region, a thinner jaw, and a higher forehead.<ref>Perrett, D.I., May, K.A. & Yoshikawa, S. 1994. Facial shape and judgements of female attractiveness. Nature 368: 239-242. </ref>
+[[File:Unnatural selection, 2 heads, one species.jpg|thumb|Neoteny and reduction in skull size – [[grey wolf]] and [[chihuahua dog|chihuahua]] skulls]]
-===Between races and among primates===
-[[Image:Sapiens neanderthal comparison.jpg|350px|right|thumb|Ashley Montagu claims modern human skulls are more neotenized than [[Neanderthal]] skulls.<ref name="Montagu" />]]
-[[Stephen Jay Gould]] objected to the ranking of races as more or less neotenous. But Gould argued that if one used the terms set forth by 1920s proponents of racial neoteny, "Asians", not whites, are "clearly" the most neotenized human race.<ref name="mismeasure">Gould, S.J. (1996). The mismeasure of man. W.W. Norton and Company, N.Y.</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>
-[[Ashley Montagu]] mirrored this statement when he stated that the "[[Mongoloid race|Mongoloid skull]], whether [[Chinese people|Chinese]] or [[Japanese people|Japanese]]" is the most neotenized human skull.<ref name="Montagu" /> Ashley Montagu further claimed that the "[[European people|European]]" skull was less neotenized than the Mongoloid, with the "[[Australian Aborigine]]" skull less neotenized than the European and the [[Neanderthal]] skull even less neotenized than the Australian Aborigine skull.<ref name="Montagu" /> Ashley Montagu claimed that humans have more neotenized skulls than ''[[Australopithecus]]''.<ref>Montagu, A. Time, Morphology, and Neoteny in the Evolution of Man.</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>
-Delbert D. Thiessen claimed that ''[[Homo sapiens]]'' are more neotenized than ''[[Homo erectus]]'', ''Homo erectus'' was more neotenized than ''Australopithicus'', [[Great Ape]]s are more neotenized than [[Old World monkey]]s and Old World monkeys are more neotenized than [[New World monkey]]s.<ref name="Bitter" />
+== In other species ==
-Nancy Lynn Barrickman claimed Brian T. Shea found by multivariate analysis that [[Bonobo]]s are more neotenized than the [[common chimpanzee]], taking into account such features as the proportionately long torso length of the Bonobo.<ref>Barrickman, N.T. (2008). Evolutionary Relationship Between Life History and Brain Growth in Anthropoid Primates. Retrieved Jun 1, 2011, from dukespace.lib.duke.edu/dspace/.../D_Barrickman_Nancy_a_200812.pdf?.</ref> Ashley Montagu believed that part of the differences seen in the morphology of "modernlike types of man" can be attributed to different rates of "neotenous mutations" in their early populations.<ref>M. F. Ashley Montagu. Time, Morphology, and Neoteny in the Evolution of Man. In American Anthropologist, Volume 57, Issue 1 (February 1955) Pages: 13-27</ref>
+[[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.]]
-====Mongoloids====
-{{main|Mongoloid}}
-[[File:Heh Miao woman Mongoloid.png|thumb|200px|Heh [[Miao people|Miao]] woman (1911)]]
-According to [[Ashley Montagu]], "The Mongoloid skull has proceeded further than in any other people."<!--pg. 13--><ref name=Montagu />  "The Mongoloid skull, whether Chinese or Japanese, has been rather more neotenized than the Caucasoid or European."<!--pg. 13--><ref name=Montagu />  "The female skull, it will be noted, is more pedomorphic in all human populations than the male skull."<!--pg. 13--><ref name=Montagu>Montagu, Ashley. Growing Young. Published by Greenwood Publishing Group, 1989. ISBN 0-89789-167-8</ref>
+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>
-In Montagu's list of "[n]eotenous structural traits in which Mongoloids... differ from Caucasoids", Montagu lists "Larger brain, larger braincase, broader skull, broader face, flat roof of the nose, inner eye fold, more protuberant eyes, lack of brow ridges, greater delicacy of bones, shallow mandibular fossa, small mastoid processes, stocky build, persistence of thymus gland into adult life, persistence of juvenile form of zygomatic muscle, persistence of juvenile form of superior lip muscle, later eruption of full dentition (except second and third molars), less hairy, fewer sweat glands, fewer hairs per square centimeter [and] long torso".<!--pg 254--><ref name=Montagu />
+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" />
-An interpretation of a claim by zoologist [[Clive Bromhall]] is that "Mongoloid races are explained in terms of being the most extreme pedomorphic humans."<ref>Moxon, Steve. [http://www.human-nature.com/nibbs/03/moxon.html Book Review: ''The Eternal Child: An Explosive New Theory of Human Origins and Behaviour'' by Clive Bromhall"], ''Human Nature'' Volume 3: 402-405, Ebury Press, 4 September 2003.</ref>
+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" />
-[[Richard Grossinger]] claimed, "The intuition that advanced human development was pedomorphic rather than recapitulationary and accelerated was disturbing to many Eurocentric nineteenth century anthropologists."<!--pg 349 --><ref name=Grossinger />  "If juvenilization was the characteristic for advanced status, then it was clear that the Mongoloid races were more deeply fetalized in most respects and thus capable of the greatest development."<!--pg 349--><ref name=Grossinger>Grossinger, Richard. ''Embryogenesis''. Published by North Atlantic Books, 2000.
-ISBN 1-55643-359-X</ref>
+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" />
-[[Stephen Oppenheimer]] claimed, "An interesting hypothesis put forward by paleontologist [[Stephen Jay Gould]] many years ago was that the package of the Mongoloid anatomical changes could be explained by the phenomenon of neoteny, whereby an infantile or childlike body form is preserved in adult life.<!--pg. 217-->  Neoteny in [[hominids]] is still one of the simplest explanations of how we developed a disproportionately large brain so rapidly over the past few million years.<!--pg. 217-->  The relatively large brain and the forward rotation of the skull on the spinal column, and body hair loss, both characteristic of humans, are found in foetal [[chimpanzee|chimps]].<!--pg. 217-->  Gould suggested a mild intensification of neoteny in Mongoloids, in whom it has been given the name pedomorphy.<!--pg. 217-->  Such a mechanism is likely to involve only a few controller genes and could therefore happen over a relatively short evolutionary period.<!--pg. 217-->  It would also explain how the counterintuitive retrousse [turned up at the end] nose and relative loss of facial hair got into the package."<!--pg. 217--><ref name=Oppenheimer>Oppenheimer, Stephen. ''The Real Eve''. Published by Carroll & Graf Publishers, 2003. ISBN 0-7867-1192-2</ref> "[D]ecrease unnecessary muscle bulk, less tooth mass, thinner bones and smaller physical size;<!--pg. 218--> ...this follows the selective adaptive model of Mongoloid evolution."<!--pg. 218--><ref name=Oppenheimer />
+[[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" />
-====Bushmen====
-{{main|Bushmen}}
-According to Ashley Montagu, Bushmen have the following neotenous traits relative to Caucasoids: "large brain", light skin pigment, less hairy, round-headed, bulging forehead, small cranial sinuses, flat roof of the nose, small face, small mastoid processes, wide eye separation, median eye fold, short stature and horizontal penis.<ref name="Montagu" />
+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 |issue=1 |pages=95–118 |jstor=2096904 |doi=10.1146/annurev.es.11.110180.000523|bibcode=1980AnRES..11...95H }}</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|bibcode=1980AnRES..11...95H }}</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>
-====Negroids====
-[[File:Women of Equatorial Africa Negroid.png|thumb|300px|Women of [[Equatorial Africa]]]]
-{{main|Negroid}}
-According to Ashley Montagu, Negroids have the following neotenous traits relative to Caucasoids: flattish [[human nose|nose]], flat roof of the nose, small ears, narrower joints, frontal skull eminences, later closure of the premaxillary sutures, less hairy, longer eyelashes and cruciform pattern of the lower second and third molars.<ref name="Montagu" />
+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|bibcode=1978CaJZ...56.1377E }}</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>
-===Psychology===
-{{see also|memory and aging}}
-Humans have been evolving toward greater "psychological-neoteny".<ref name="Genius">Charlton BG. The rise of the boy-genius: psychological neoteny, science and modern life. Medical Hypotheses. 2006; 67: 679-81 </ref> Highly-educated people and eminent scientists usually demonstrate more neotenous psychological traits,<ref name=Charlton>See Charlton BG, [http://www.hedweb.com/bgcharlton/ed-boygenius.html The rise of the boy-genius: psychological neoteny, science and modern life]. ''Medical Hypotheses''. 2006; 67: 679–81.</ref> and students with more of a "baby face" tend to "outperform" their less-neotenized peers in school.<ref>Zebrowitz, L. A., Andreoletti, C., Collins, M. A., Lee, S. Y., & Blumenthal, J. (1998). Bright, bad, babyfaced boys: Appearance stereotypes do not always yield self-fulfilling prophecy effects. Journal of Personality & Social Psychology, 75, 1300-1320. </ref> In fact, the ability of an adult human to learn has long been considered a neotenous trait.<ref>Young J.Z. 1957; 2nd ed 1975. ''The life of mammals''. Oxford.</ref> Physical neotenization in humans has, likewise, caused psychologically neotenous traits in humans: curiosity, playfulness, affection, sociality and an innate desire to cooperate.<ref>Lehman, A. (2010). Evolution, Autism and Social Change. neoteny.org.</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>
-===Specific neotenies===
-Populations with a history of dairy farming have evolved to be [[lactose tolerance|lactose tolerant]] in adulthood whereas other populations generally lose the ability to break down lactose as they grow into adults. <ref name="Samuel">Johnson, S. Religion, Science and other Neotenous Behaviour. www.ugr.es/~sam/index_archivos/Essays/Neoteny.pdf</ref>
+== Subcellular neoteny ==
-===Down syndrome===
-[[Down syndrome]] neotenizes the brain and body to the fetal state.<ref>Opitz, John M. & Gilbert-Barness, Enid F.  (1990) Reflections on the Pathogenesis of Down Syndrome.  American Journal of Medical Genetics 7: p. 44 pmid 2149972</ref> Down syndrome is characterized by decelerated maturation (neoteny), incomplete morphogenesis (vestigia) and [[atavism]]s.<ref>Optiz, J.M. (1990). Reflections on the pathogenesis of Down syndrome. In American Journal of Medical Genetics Supplement. 7:38.</ref> Dr. Weihs considers Down syndrome to be a condition of "neoteny" that makes people "like a baby."<ref name="Richards" />
+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>
-He notes both the physical neoteny of people with Down syndrome: "round in shape," "bowed legs which tend to be short," "slanty eyes," a "long tongue" and "short fingers," and their mental neoteny: "unsexual," "playful," "affectionate," "mischievous" and "[[Imitation|imitative]]".<ref name="Richards">Richards, M.C. Toward wholeness: Rudolf Steiner education in America. 1980. University Press of New England, N.H.</ref>
-===Anime and manga===
+== See also ==
-{{See also|Kawaii}}
-Dr. [[Thomas Lamarre]], professor of East Asian Studies and Art History at [[McGill University]], claimed that after [[World War II]], Japanese people as shown in their {{nihongo|[[manga]]|漫画}} and {{nihongo|[[anime]]|アニメ}} became "fascinated" with neoteny and "[[cuteness]]".<ref>Lamarre, Thomas. [http://howietsui.com/pdf/concordiaprogram.pdf "The Theatre of Species: Race and Animals in Manga and Anime"], ''Comics, Japanese Popular Culture and Contemporary Art'', Concordia University Fine Arts Department of Art History. Retrieved May 27, 2011.</ref>
+* [[Ageing]]
-==In other species==
+* [[Cuteness]]
-* The [[axolotl]] is a salamander that retains its juvenile aquatic form throughout adulthood and [[tiger salamander]] and [[Rough-skinned Newt]] can both retain gills into adulthood.<ref>C. Michael Hogan (2008) ''Rough-skinned Newt (Taricha granulosa)'', Globaltwitcher, ed. N. Stromberg [http://www.globaltwitcher.com/artspec_information.asp?thingid=43182]</ref>
+* [[Kawaii]]
-* Flightless [[bird]]s' physical proportions resemble those of the chicks of flighted birds;
+* [[Larviform female]]
-* A plant species in the genus ''[[Oreostylidium]]'' neotenized to become mature earlier than other species in its genus in response to selective pressure.<ref>{{citation|last1 = Wagstaff|first1 = S J|last2 = Wege|first2 = J|year = 2002|url = http://www.amjbot.org/cgi/content/full/89/5/865|title = Patterns of diversification in New Zealand Stylidiaceae|journal = American Journal of Botany|volume = 89|issue = 5|pages = 865–874|doi = 10.3732/ajb.89.5.865}}.</ref>
+* [[Moe (slang)]]
+* [[Neotenic complex syndrome]]
+* [[Neotenin]]
-===Domestication===
+== References ==
+{{Reflist|30em}}
-Domestication has involved selection for behavioral characteristics that characterize young animals so, since "behavior is rooted in biology", domestication has resulted in an array of similar neotenous physical traits having arisen in various domesticated animals.<ref name="Trut">Trut, L. N. (1999). Early Canid Domestication: The Farm-Fox Experiment ''American Scientist.'' 87(2), 160-169. </ref>  Such neotenous physical traits in domesticated animals such as dogs, pigs, cats, and recently [[Domesticated silver fox|foxes]] are floppy ears, changes in reproductive cycle, curly tails, piebald coloration, fewer or shortened vertebra,<ref name="Trut" /> large eyes, rounded forehead, large ears and shortened muzzle.<ref>Bertone, J. (2006). Equine geriatric medicine and surgery. Saunders, MI.</ref>
-==See also==
+== Further reading ==
-*[[Cuteness]]
-*[[Sexual selection]]
-*[[Ageing]]
+* Bergstorm, Carl T. & Dugatkin, Lee Alan (2012). ''Evolution'', W.W. Norton {{ISBN|039391349X}}
-==References==
-{{reflist}}
+{{genarch}}
 [[Category:Developmental biology]]
 [[Category:Evolutionary biology]]
+[[Category:Taxonomy (biology)]]
-[[ca:Neotènia]]
-[[cs:Neotenie]]
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-[[es:Neotenia]]
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-[[he:נאוטניה]]
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-[[kk:Неотения]]
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