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'''Neoteny''' ({{IPA|niː.ɒ.tə.niː}}) is the retention, by adults in a species, of traits previously seen only in juveniles ([[pedomorphosis]]/paedomorphosis), 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. Ultimately this process results in the retention, in the adults of a [[species]], of juvenile physical characteristics well into maturity. The [[English language|English]] word ''neoteny'' is borrowed from the [[German language|German]] ''Neotenie'', the latter constructed from the [[Greek language|Greek]] ''νέος'' (young) and ''τείνειν'' (to extend). The standard [[adjectival]] form is "neotenous", although "neotenic" is often used.

In [[vertebrate]] biology, neoteny is most easily identified when sexually mature, completely viable juveniles or larvae are found. 

Specific individual traits that differ in descendant organisms, when compared to ancestors, are sometimes called ''neotenies''; [[human]]s, for example, appear to have several neotenies in comparison to [[chimpanzee]]s.

==Neoteny in evolution==

Neoteny plays a role in [[evolution]], as a means by which, over generations, a species can undergo a significant physical change. In such cases, a species’ neotenous form becomes its “normal” mature form, no longer dependent upon environmental triggers to inhibit maturity. The mechanism for this could be a [[mutation]] in, or interactions between: [[gene]]s involved in maturation, changing their function to impede this process.

Neoteny is not the only contributing factor affecting maturation in species that may have undergone neotenous changes over the course of their evolution, and its actual involvement in the following examples is not well understood: 
* flightless [[bird]]s&mdash;physical proportions resemble those of the chicks of flighted birds;
* [[human]]s&mdash;with traits such as sparse body hair and enlarged heads reminiscent of baby primates. [[Lactose tolerance]] in adults is a form of neoteny now considered normal in some European populations and their descendants while most other humans are lactose intolerant as adults. It corresponds to a mutation that permits the digestion of lactose beyond the lactation period.
* pets, such as [[Dog#Neoteny in the rapid evolution of diverse dog breeds|dog]]s&mdash;which share many physical features with the immature [[wolf]] (these same traits were found during the development of the [[tame silver fox]]).  Such puppy-like traits may have made early dogs seem "cute" and less threatening than wolves, leading to both natural and artificial selection of such dogs.

It is possible that the origin of the [[chordates]] (the phylum including all vertebrates) was the result of an instance of neoteny. Molecular evidence suggests that the nearest relatives of the chordates are the [[tunicates]], marine filter feeders. Although [[sessile]] in their adult, sexually mature form, tunicates have a [[motile]] larval dispersal form, which has a [[notochord]] similar to that found in chordates. At some point, the motile larvae of the tunicate became sexually mature before [[metamorphosis]]. As a sexually active [[pelagic]] organism it had considerable feeding and habitat colonization advantages over the sessile form, so was at an evolutionary advantage. However, the alternative - that the sessile form developed later and the pelagic form was ancestral - is also thought possible.[citation needed]

==Neoteny in humans==
Neoteny in humans can be seen in different aspects. It can be compared with other [[great ape]] species, between the sexes and between individuals.

===Other species===
There is controversy over whether adult humans exhibit certain neotenous features, or juvenile characteristics, that are not evidenced in other great ape species. [[Stephen Jay Gould]] was an advocate of the view that humans are a neotenous species of chimpanzee; the argument being that juvenile chimpanzees have an almost-identical bone structure to humans, and that the chimpanzee’s ability to learn seems to be cut off upon reaching maturity.

===Sexes===
While neoteny is not necessarily a physical state experienced by humans, [[paedomorphic]] characteristics in women are widely acknowledged as desirable by men [http://en.wikipedia.org/wiki/Physical_attractiveness#Determinants_of_female_physical_attractiveness]. For instance, [[vellus hair]] is a juvenile characteristic. However, while men develop longer, coarser, thicker, and darker [[terminal hair]] through [[sexual differentiation]], women do not, leaving their vellus hair visible.

[[Desmond Morris]] discusses the importance of neoteny in human biology in ''[[The Naked Ape]]'', ''[[The Human Animal]]'', and ''[[The Human Zoo (book)|The Human Zoo]]''.

===Individuals===
Paedomorphic variations not only exist between the sexes, but also between individuals, with some people displaying more characteristics of neoteny than others. This trend carries over to variations among ethnic groups as well.

Bruce Charlton, Reader in evolutionary psychiatry at [[Newcastle University]] [[U.K.]], suggests that there may be such a thing as "[[psychological neoteny]]." <ref>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. The article is also discussed by Matthew Hutson in [http://www.psychologytoday.com/articles/pto-20061201-000002.html The Peter Pan-demic], ''[[Psychology Today]]'' magazine, Nov/Dec 2006,  and by Clay Risen in [http://www.nytimes.com/2006/12/10/magazine/10section3a.t-3.html?ex=1323406800&en=3f6e0203d3bf81e6&ei=5090 Psychological Neoteny], ''[[The New York Times Magazine]]'', December 10, 2006</ref> Due to recent changes in culture, he says,  “In a psychological sense, some contemporary individuals never actually become adults.” Delayed maturity may be a consequence of later parenthood, itself caused by more prolonged formal education - especially among women <ref>Charlton BG, [http://www.hedweb.com/bgcharlton/psychological-neoteny.html Psychological neoteny and higher education: Associations with delayed parenthood] ''Medical Hypotheses''. 2007; 69: 237-40.</ref>

==Animal kingdom==
One example of a neotenic trait in [[vertebrate]]s is the [[salamander]] species [[axolotl]], which usually remains fully aquatic as it matures.  Other salamanders, such as the widespread [[tiger salamander]] of North America, may retain the external gills usually only present in immature individuals, as adults in some populations in marginal habitats.

==Neoteny and progenesis==
Neoteny and [[progenesis]] are both mechanisms that result in [[paedomorphosis]]. Neoteny delays physiological, but not sexual, maturity. Comparatively, [[progenesis]] speeds up sexual, but not physiological, maturity. Progenetic organisms achieve sexual maturity in their juvenile state. This is most commonly found among certain [[amphibia]]ns and [[insect]]s.

==See also==
*[[Cuteness]]
*[[Heterochrony]]
*[[Paedogenesis]]
*[[Pedomorphosis]]

==References==
{{reflist|2}}

==External links==
*[http://dannyreviews.com/h/Ontogeny_and_Phylogeny.html DannyReviews.com]&mdash;''Ontogeny and Phylogeny'', [[Stephen Jay Gould]] (book review), [[Danny Yee]] (October 16, 1992)
*[http://www.davidbrin.com/neotenyarticle1.html DavidBrin.com]&mdash;“Neoteny and Two-Way Sexual Selection in Human Evolution: A Paleo-Anthropological Speculation on the Origins of Secondary-Sexual Traits, Male Nurturing and the Child as a Sexual Image,” [[David Brin]], PhD
*[http://www.neoteny.org/ Neoteny.org]&mdash;“Neoteny: The multidisciplinary implications of heterochronic theory”
*[http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11953945 NIH.gov]&mdash;“Ontogenetic study of the skull in modern humans and the common chimpanzees: neotenic hypothesis reconsidered with a tridimensional Procrustes analysis,” X. Penin, C. Berge, M. Baylac, ''[[American Journal of Physical Anthropology]]'', vol 118, no 1, p 50-62 (May, 2002)
*[http://www.nhm.org/exhibitions/dogs/evolution/neoteny.html NHM.org]&mdash;“Neoteny/Juvenilization: Some dogs look and act forever young,” [[Natural History Museum of Los Angeles County]]
*Trut, Lyudmila N. (1999). "[http://www.floridalupine.org/publications/PDF/trut-fox-study.pdf Early Canid Domestication: The Farm-Fox Experiment]" ''American Scientist.'' '''87'''(2), 160-169. (A [[Russia]]n study of pedomorphosis in a 40-year breeding program to domesticate [[red fox|silver foxes]].)

[[Category:Developmental biology]]
[[Category:Evolution]]
[[Category:Evolutionary biology]]

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