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For the topic of soil formation, see Pedogenesis.
Human body proportion changes with age

Neoteny (/nˈɒtɨni/ /nˈɒtni/[1][2][3] or /nˈɒtəni/[4]), also called juvenilization,[5] is one of the three ways by which paedomorphism can arise. Paedomorphism or paedomorphosis is the retention by adults of traits previously seen only in the young, and is a subject studied in the field of developmental biology. In neoteny, the physiological (or somatic) development of an organism (typically an animal) is slowed or delayed. In contrast, in progenesis, sexual development occurs faster. Both processes result in paedomorphism.[6] 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.[7]

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).[8]

The word neoteny is borrowed from the German Neotenie, the latter constructed from the Greek νέος (neos, "young") and τείνειν (teínein, "to extend"). The adjective form of the word is either "neotenic" or "neotenous".[9] For the opposite of "neotenic", different authorities use either "gerontomorphic"[10] or "peramorphic".[11]

In humans[edit]

Neotenic traits in humans[edit]

Physical anthropologist Barry Bogin considers Betty Boop to be an example of neoteny[12]

These are neotenic traits in humans: flattened face,[5] broadened face,[13] large brain,[5] hairless body,[5] hairless face,[14] small nose,[14] reduction of brow ridge,[5] small teeth,[5] small upper jaw (maxilla),[5] small lower jaw (mandible),[5] thinness of skull bones,[13] limbs proportionately short compared to torso length,[13] longer leg than arm length,[15] larger eyes,[16] and upright stance.[10][17]

Human evolution[edit]

Main article: 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".[18] 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."[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."[19] 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).[20]

Stanley Greenspan and Stuart G. Shanker proposed a theory in 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 signaling, neotenous features, such as hair loss, allow for more efficient and rapid communication of socially important messages that are based on facially expressive emotional signaling.[21]

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.[22] 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.[22][23] 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.[10] Brian K. Hall also cites the long legs of humans as a peramorphic trait, which is in sharp contrast to neoteny.[11]

On the balance, an all or nothing approach could be regarded as pointless, with a combination of heterochronic processes being more likely and more reasonable (Vrba, 1996).

Between sexes[edit]

Ashley Montagu said that the following neotenous traits are in women when compared to men: more delicate skeleton, smoother ligament attachments, smaller mastoid processes, reduced brow ridges, more forward tilt of the head, narrower joints, less hairy, retention of 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.[5]

Cro-Magnon humans (40,000 to 10,000 years ago) differed from co-existing Neanderthals in the following ways: "higher forehead, less prominent brow ridges, smaller teeth, less robust bodies, and reduced sexual dimorphism."[24]

Attractive women's faces[edit]

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.[25] Using a panel of Asian, Hispanic and 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"[26] and his study led him to conclude that "large eyes" were the most "effective" of the "neonate cues".[26] Cunningham also said that "shiny" hair may be indicative of "neonate vitality".[26]

Cunningham said that there was a "difference" in the preferences of Asian and White judges. Cunningham said that Asian judges preferred women with "less mature faces" and smaller mouths than the White judges.[26] 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 he concluded that "ethnocentrism was not a primary determinant of Asian preferences."[26] Using a panel of Blacks and Whites as judges, Cunningham said that more neotenous faces were perceived as having both higher "femininity" and "sociability".[26]

In contrast, Cunningham said that faces that were "low in neoteny" were judged as "intimidating".[26] 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".[26] In a study of Italian women who have won beauty competitions, the study said that the women had faces characterized by more "babyness" traits compared to the "normal" women used as a reference.[27] In a study of sixty Caucasian female faces, the average facial composite of the fifteen faces considered most attractive differed from the facial composite of the whole by having a reduced lower facial region, a thinner jaw, and a higher forehead.[28]

Between races and among primates[edit]

Ashley Montagu said modern human skulls are more neotenized than Neanderthal skulls.[5]

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" are "clearly" the most neotenized human race.[20]

Similarly, Ashley Montagu said that the "Mongoloid skull, whether Chinese or Japanese" is the most neotenized human skull.[5] Ashley Montagu further said that the "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.[5] Ashley Montagu said that humans have more neotenized skulls than Australopithecus.[29]

Delbert D. Thiessen said that Homo sapiens are more neotenized than Homo erectus, Homo erectus was more neotenized than Australopithecus, Great Apes are more neotenized than Old World monkeys and Old World monkeys are more neotenized than New World monkeys.[19]

Nancy Lynn Barrickman said that Brian T. Shea concluded by multivariate analysis that Bonobos are more neotenized than the common chimpanzee, taking into account such features as the proportionately long torso length of the Bonobo.[30] Ashley Montagu said 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.[31]


Main article: Mongoloid
Heh Miao woman (1911)

Ashley Montagu said, "The Mongoloid skull has proceeded further than in any other people."[5] "The Mongoloid skull, whether Chinese or Japanese, has been rather more neotenized than the Caucasoid or European."[5] "The female skull, it will be noted, is more pedomorphic in all human populations than the male skull."[5]

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".[5]

An interpretation of a claim by zoologist Clive Bromhall is that "Mongoloid races are explained in terms of being the most extreme pedomorphic humans."[32]

Richard Grossinger said, "The intuition that advanced human development was pedomorphic rather than recapitulationary and accelerated was disturbing to many Eurocentric nineteenth century anthropologists."[33] "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."[33]

Stephen Oppenheimer said, "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. 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. 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 chimps. Gould suggested a mild intensification of neoteny in Mongoloids, in whom it has been given the name pedomorphy. Such a mechanism is likely to involve only a few controller genes and could therefore happen over a relatively short evolutionary period. It would also explain how the counterintuitive retrousse [turned up at the end] nose and relative loss of facial hair got into the package."[34] "[D]ecrease unnecessary muscle bulk, less tooth mass, thinner bones and smaller physical size; ...this follows the selective adaptive model of Mongoloid evolution."[34]

San people[edit]

Main article: San people

Ashley Montagu said that the San 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.[5]


Main article: Negroid

Ashley Montagu said that Negroids have the following neotenous traits relative to Caucasoids: flattish 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.[5]


Humans have been evolving toward greater "psychological neoteny."[35] Dr. Bruce Charlton, a Newcastle University psychology professor, said what looks like immaturity — or in his terms, the “retention of youthful attitudes and behaviors into later adulthood” — is actually a valuable developmental characteristic, which he calls psychological neoteny.[36] Highly educated people and eminent scientists demonstrate more neotenous psychological traits.[37] In fact, the ability of an adult human to learn is considered a neotenous trait.[38] Physical neotenization in humans has, likewise, caused psychologically neotenous traits in humans: curiosity, playfulness, affection, sociality and an innate desire to cooperate.[39]

Specific neotenies[edit]

Populations with a history of dairy farming have evolved to be lactose tolerant in adulthood whereas other populations generally lose the ability to break down lactose as they grow into adults.[40]

Down syndrome[edit]

Down syndrome neotenizes the brain and body.[41] Down syndrome is characterized by decelerated maturation (neoteny), incomplete morphogenesis (vestigia) and atavisms.[42] Dr. Weihs[who?] considers Down syndrome to be a condition of "neoteny" that makes people "like a baby."[43]

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 "imitative".[43]

Anime and manga[edit]

See also: Kawaii

Dr. Thomas LaMarre, professor of East Asian Studies and Art History at McGill University, said that after World War II, Japanese people as shown in their manga (漫画?) and anime (アニメ?) became "fascinated" with neoteny and "cuteness".[44]

Neoteny in other species[edit]

Neoteny has been observed in many other species. Neoteny in amphibians seems to be the most widely studied aside from humans; many examples of neoteny in amphibians stem from studies done mainly on salamanders. There is also a general prevalence of increased neoteny within domesticated animals like dogs. Neoteny has also been noted in species similar to humans, like chimpanzees. The neotenous traits in chimpanzees that resemble those within humans may give some insight into the evolutionary history of humans. What can be gathered from many studies on neoteny is that organisms with similar lineages tend to neotenize similar features, meaning they retain related features from the juvenile form into adulthood. Finally, there are two main reasons for the occurrence of neoteny: it can either be a result of the benefit of retaining juvenile characteristics due to an environment that favors those characteristics over the adult form, or the retention of juvenile characteristics leads to greater survival because those characteristics are less costly in terms of energy expenditure.

It is important to note the difference between partial and full neoteny when looking at other species in order to distinguish between juvenile traits that are only advantageous in the short term and traits that provide a benefit throughout the organism’s life; this might then provide some insight into the cause of neoteny in those species. Partial neoteny is the retention of the larval form beyond the usual age of maturation with the possibility of the development of sexual organs progenesis, but eventually the organism still matures into the adult form; this can be seen in Lithobates clamitans. Full neoteny is seen in Ambystoma tigrinum. This species is part of a larger group, perrenobranchiates, which remain in their larval form for the duration of their life. This means that they are capable of reproducing and they do not mature into adult forms. [45] The species Rana Clamata exhibits partial neoteny when it delays its maturation through the winter season because it is not advantageous for it to metamorphose into the adult form until there are more resources available since it can find those resources much more easily in the larval form. This would fall under both of the main causes of neoteny; the energy required to survive in the winter as a newly formed adult is too costly, so the organism exhibits neotenous characteristics until a time when it is capable of better survival as an adult. Ambystoma tigrinum retains its neotenous features for a similar reason, however the retention is permanent due to the lack of resources available throughout its lifetime. This is another example of an environmental cause of neoteny in that the species retains juvenile characteristics because the environment limits the ability of the organism to fully come into its adult form. A few species of birds show partial neoteny. A couple examples of such species are Chiroxiphia linearis and Chiroxiphia caudata. The males of both species retain their juvenile plumage into adulthood, but they eventually lose it once they are fully mature. [46] In certain species of birds the retention of juvenile plumage is often linked to the molting times within each species. In order to ensure there is no overlap between the molting and mating times, the birds may show partial neoteny in regards to their plumage so that the males do not attain their bright adult plumage before the females are prepared to mate. In this instance, neoteny is present because there is no need for the males to molt early and it would be a waste of energy for them to try to mate when the females are not yet prepared.

Neoteny is seen more in domesticated animals like dogs and mice.[47] 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.[47] 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. Oftentimes, 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 reproductive cycle, curly tails, piebald coloration, fewer or shortened vertebra, large eyes, rounded forehead, large ears, and shortened muzzle.[48][49]

Neoteny is commonly seen in flightless insects like the females in the order Strepsiptera. The flightless trait in insects has evolved many separate times; environments that may have contributed to the separate evolution of this trait are: high altitudes, isolation on islands, and insects that reside in colder climates.[50] These environmental factors may be responsible for the flightless trait, because in these situations it would be disadvantageous to have a population that is more dispersed, so flightlessness would be favored due to the boundaries it poses to dispersal. Also, in cooler temperatures heat is lost more rapidly through wings, thus the circumstance favors flightlessness. 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. Flightlessness in some female insects has been linked to higher fecundity, this would increase the fitness of the individual because the female is producing more offspring and therefore passing on more of her genes.[51] In those instances, neoteny occurs because it is more advantageous for the females to remain flightless in order to conserve energy which thereby increases their fecundity. Aphids are a great example of insects that may never develop wings due to their environmental setting. If resources are abundant there is no need to grow wings and disperse. When the nutrition of a host plant is abundant aphids may not grow wings and stay there for the duration of their life, however if the resources become diminished the offspring may develop wings in order to disperse to other host plants.[52]

Two common environments that tend to favor neoteny are high-altitude and cool environments because neotenous individuals have a higher fitness than those that metamorphose into the adult form. This is because the energy required for metamorphosis is too costly for the individual’s fitness, also the conditions favor neoteny due to the ability of neotenous individuals to utilize the available resources more easily.[53] This trend can be seen in the comparison of salamander species of lower and higher altitudes. The neotenous individuals have higher survivorship as well as higher fecundity than the salamanders that had gone to the adult form in the higher altitude and cooler environment.[54] Insects in cooler environments tend to show neoteny in flight because wings have a high surface area and lose heat quickly, thus it is not advantageous for insects in that environment to metamorphose into adults.[55]

Many species of salamander, and amphibians in general, are known to have neotenized characteristics because of the environment they live in. The axolotl is a species of salamander that retains its juvenile aquatic form throughout adulthood, which is an excellent example of full neoteny.[45] Gills are a common juvenile characteristic in amphibians that are kept after maturation; an example of this would be a comparison of the tiger salamander and the rough-skinned newt, both of which retain gills into adulthood.[45] These species are better able to survive when they retain certain juvenile features, like gills, that allow them access to both aquatic and land environments.

Pygmy chimpanzees (Bonobos) share many physical characteristics with humans. A prime example are their neotenous skulls.[56] The shape of their skull does not change into adulthood, it only increases in size. This is due to sexual dimorphism and an evolutionary change in timing of development.[57] Juveniles became sexually mature before their bodies had fully developed into adulthood, and due to some selective advantage the neotenic structure of the skull remained in later generations.

More examples of neoteny can be seen in these other species:

1. Species in which energy costs result in neoteny-

2. Species in which the environmental conditions cause neoteny-

In design[edit]

Neoteny in design differs from biological neoteny as it refers to the purposeful integration and simulation of neotenous traits in anything that requires technical design from fictional characters, clothing, cartoons, art, food or any other form of artistic expression. By inserting neotenous traits, it can make certain subjects gain a cuter, more innocent or more wholesome appearance. Neoteny in design seeks to appeal to potential consumers in hopes of either increasing sales or improving the reception or approval of the target or potential audience by inciting an adoring reaction to something intended to be "cute". A popular series featuring cute characters is the Pokémon franchise. For more information on cuteness in Japanese popular culture see kawaii. For a specific type of designed cuteness, see moe.

By making their product or artwork display neotenous traits, designers attempt to sway people to enjoy or desire their product, because it appears childish, adorable, soft or otherwise desirable. By making a product cute, the nucleus accumbens in the human brain is targeted and elicits a protective or coddling response, which encourages an individual to acquire (purchase) said item. By designing items, characters, food or anything else in this manner, product designers attempt to create the same reaction to a product that a human baby could create. This is one reason that certain cute products become so collectable and sought after, such as stuffed animals, dolls, toys, miniature figurines and models and even pets. Through design, producers can encourage the same protective feeling in people as what would usually be felt when seeing a lost child.

In another sense, neoteny in design can also pertain to making media seem more humorous or carefree. Cartoons marketed to children and their parents will usually not deal with adult problems or use crude language because this makes them non-childlike (or non-neotenous). Crude humor or slapstick comedy often rely on elements that even young children find amusing such as farting, burping, silly faces and minor physical harm. Such comedy is often labeled as crude because it calls upon neotenous habits that are generally seen as being outside of civilized society.

See also[edit]


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