Neoteny

neotenicpaedomorphicpaedomorphosisneotenouspedomorphosispedomorphicprogenesispaedogenesisyouthfulnessneotenes
Neoteny, also called juvenilization, is the delaying or slowing of the physiological (or somatic) development of an organism, typically an animal.wikipedia
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Neoteny in humans

neotenousmodern humansneoteny
Neoteny is found in modern humans.
Neotenic features of the head include the globular skull; thinness of skull bones; the reduction of the brow ridge; the large brain; the flattened and broadened face; the hairless face; hair on (top of) the head; larger eyes; ear shape; small nose; small teeth; and the small maxilla (upper jaw) and mandible (lower jaw).

Larva

larvaelarvalgrubs
Some authors define paedomorphism as the retention of larval traits, as seen in salamanders.
This is a type of neoteny.

Salamander

salamandersUrodelaurodele amphibians
Some authors define paedomorphism as the retention of larval traits, as seen in salamanders.
Some neotenic species such as the mudpuppy (Necturus maculosus) retain their gills throughout their lives, but most species lose them at metamorphosis.

Sexual selection in humans

Sexual selection in human evolutionsexual selectionsexually selected
These neotenic changes may have been brought about by sexual selection in human evolution.
The role of sexual selection in human evolution has not been firmly established although neoteny has been cited as being caused by human sexual selection.

Evolutionary developmental biology

evo-devoevolutionary developmental biologistevolutionary development
Such retention is important in evolutionary biology, domestication and evolutionary developmental biology.
The evolutionary embryologist Gavin de Beer anticipated evolutionary developmental biology in his 1930 book Embryos and Ancestors, by showing that evolution could occur by heterochrony, such as in the retention of juvenile features in the adult.

Human evolution

evolutionearly manevolution of humans
Some evolutionary theorists have proposed that neoteny was a key feature in human evolution.
The smaller birth canal became a limiting factor to brain size increases in early humans and prompted a shorter gestation period leading to the relative immaturity of human offspring, who are unable to walk much before 12 months and have greater neoteny, compared to other primates, who are mobile at a much earlier age.

Amphibian

Amphibiaamphibiansamphibious
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.
Members of several salamander families have become paedomorphic and either fail to complete their metamorphosis or retain some larval characteristics as adults.

Stephen Jay Gould

Stephen J. GouldGouldGould, Stephen Jay
In his 1977 book Ontogeny and Phylogeny, 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.
In this book he emphasized the process of heterochrony, which encompasses two distinct processes: neoteny and terminal additions.

Ontogeny and Phylogeny (book)

Ontogeny and Phylogeny
In his 1977 book Ontogeny and Phylogeny, 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.
The second half of the book details how modern concepts such as heterochrony (changes in developmental timing) and neoteny (the retardation of developmental expression or growth rates) influence macroevolution (major evolutionary transitions).

Axolotl

Ambystoma mexicanumaxolotlsA-X-O-L-O-T-L
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. Axolotl and olm are species of salamander that retains their juvenile aquatic form throughout adulthood, examples of full neoteny. Full neoteny is seen in Ambystoma mexicanum and some populations of Ambystoma tigrinum, which remain in their larval form for the duration of their life.
The axolotl (, from ; plural axolotls or rarely axolomeh ), Ambystoma mexicanum, also known as the Mexican walking fish, is a neotenic salamander related to the tiger salamander.

Julius Kollmann

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.
In 1884 Kollmann introduced the term "neoteny" to define the transformation process where animals such as newts mature sexually while still in the larval form.

Heterochrony

heterochronicperamorphicperamorphosis
Both neoteny and progenesis result in paedomorphism (or paedomorphosis), a type of heterochrony.
Paedomorphosis can be the result of neoteny, the retention of juvenile traits into the adult form as a result of retardation of somatic development, or of progenesis, the acceleration of developmental processes such that the juvenile form becomes a sexually mature adult.

Strepsiptera

strepsipteranstylopidTwisted-wing flies
Neoteny is commonly seen in flightless insects like the females in the order Strepsiptera.
Females, in all families except the Mengenillidae, are not known to leave their hosts and are neotenic in form, lacking wings, legs, and eyes.

Olm

Proteus anguinusProteusblack olm
Axolotl and olm are species of salamander that retains their juvenile aquatic form throughout adulthood, examples of full neoteny.
It also exhibits neoteny, retaining larval characteristics like external gills into adulthood, like some American amphibians, the axolotl and the mudpuppies (Necturus).

Tiger salamander

Ambystoma tigrinumEastern tiger salamanderA. tigrinum
Full neoteny is seen in Ambystoma mexicanum and some populations of Ambystoma tigrinum, which remain in their larval form for the duration of their life.
These are the neotenes, and are particularly common where terrestrial conditions are poor.

Bonobo

bonobosPan paniscuspygmy chimpanzee
Pygmy chimpanzees (bonobos) share many physical characteristics with humans.
Multivariate analysis has shown bonobos are more neotenized than the common chimpanzee, taking into account such features as the proportionately long torso length of the bonobo.

Northwestern salamander

Ambystoma gracileA. gracileAmybstoma gracile
In other species, environmental conditions cause neoteny, as in the northwestern salamander (Ambystoma gracile), where higher altitude is correlated with greater neotenic tendencies, perhaps to help conserve energy as mentioned above.
Populations with neotenic adults are widespread; the frequency of gilled adults increases with altitude such that adults at low and intermediate altitudes are almost all terrestrial, while adults at very high elevations are mostly neotenic.

Cuteness

cutejuvenile characteristicsappealing
Desmond Collins, who was an Extension Lecturer of Archaeology at London University, said that the lengthened youth period of humans is part of neoteny.

Metamorphosis

metamorphosemetamorphosedmetamorphosing
Another couple of main points to note about insects are that the females in certain groups become sexually mature without metamorphosing into adulthood, and some insects which grow up in certain conditions do not ever develop wings.
The Salamander development is highly diverse; some species go through a dramatic reorganization when transitioning from aquatic larvae to terrestrial adults, while others, such as the Axolotl, display paedomorphosis and never develop into terrestrial adults.

Physiology

physiologistphysiologicalphysiologically
Neoteny, also called juvenilization, is the delaying or slowing of the physiological (or somatic) development of an organism, typically an animal.

Somatic (biology)

somaticsomasomatic cells
Neoteny, also called juvenilization, is the delaying or slowing of the physiological (or somatic) development of an organism, typically an animal.

Puberty

pubescentpubescencesexual development
In progenesis (also called paedogenesis), sexual development is accelerated.

Evolutionary biology

evolutionary biologistevolutionary biologistsevolutionary
Such retention is important in evolutionary biology, domestication and evolutionary developmental biology.

Domestication

domesticateddomesticdomesticate
Such retention is important in evolutionary biology, domestication and evolutionary developmental biology.

Ashley Montagu

Ashley MontagueMontagu, AshleyIsrael Ehrenberg
The origins of the concept of neoteny have been traced to the Bible (as argued by Ashley Montagu) and to the poet William Wordsworth's "The Child is the father of the Man" (as argued by Barry Bogin).