Hubbry Logo
NeotenyNeotenyMain
Open search
Neoteny
Community hub
Neoteny
logo
7 pages, 0 posts
0 subscribers
Be the first to start a discussion here.
Be the first to start a discussion here.
Contribute something
Neoteny
Neoteny
Neoteny
View on Wikipedia
from Wikipedia

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

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

History and etymology

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

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

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

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

In humans

[edit]
Main article: Neoteny in humans

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

In domestic animals

[edit]
Further information: Domestication of animals

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

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

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

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

In other animals

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

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

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

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

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

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

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

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

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

Subcellular neoteny

[edit]

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

See also

[edit]

References

[edit]

Further reading

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Neoteny

View on Grokipedia
from Grokipedia
Neoteny is a biological process in which an organism retains juvenile or larval characteristics into adulthood, typically through the retardation of somatic development relative to the timing of sexual maturation, resulting in a form of paedomorphosis known as paedomorphosis by prolongation of growth. This heterochronic shift distinguishes neoteny from progenesis, where sexual maturity accelerates while somatic traits remain juvenile, and has been observed across taxa, particularly in amphibians such as the axolotl (Ambystoma mexicanum), which maintains external gills, aquatic lifestyle, and larval morphology throughout life despite reproductive capability. In evolutionary contexts, neoteny facilitates adaptation by preserving traits advantageous in stable or protected environments, as seen in facultative neoteny among salamanders where individuals may bypass metamorphosis under favorable conditions. Hypotheses regarding human evolution invoke neoteny to explain the retention of ape-like juvenile features, including a globular skull and reduced facial prognathism, with molecular evidence indicating delayed gene expression patterns in the brain that prolong developmental plasticity. These neotenic traits in humans, such as relatively large eyes and small noses, can evoke psychological responses including protective instincts and attraction through the "baby schema" effect, similar to reactions elicited by infants or young animals. While empirical support exists for transcriptional neoteny in human prefrontal cortex development, broader claims linking it causally to cognitive advancements remain subjects of ongoing research, emphasizing heterochrony's role in morphological and physiological diversity without overstating adaptive universality.

Definition and Conceptual Foundations

Precise Biological Definition

Neoteny constitutes a distinct category of , defined as an evolutionary shift involving a reduction in the rate of somatic development relative to the ancestral condition, while reproductive maturation proceeds at a comparable or unaltered pace. itself encompasses any genetically controlled alteration in the timing, rate, or duration of developmental events compared to an , often manifesting as changes in growth trajectories that yield morphological novelty. In neoteny, this deceleration specifically targets non-reproductive somatic traits, such as skeletal or organ maturation, leading to the retention of juvenile or larval features—e.g., proportions, pigmentation, or appendages—within sexually mature adults. This process differs from progenesis, the other primary mechanism producing paedomorphosis (the broader phenotypic outcome of juvenilized adulthood), wherein overall development is truncated by an acceleration of sexual maturation, affecting the entire rather than selectively slowing somatic growth. Neoteny's selective impact on growth rates enables modular evolutionary changes, where specific body regions or traits retain ancestral juvenile forms without compromising reproductive timing, as evidenced in quantitative analyses of developmental trajectories in vertebrates. Genetic underpinnings, such as regulatory shifts in hormone-sensitive pathways, underpin this rate disparity, though neoteny is observable phenotypically without necessitating molecular dissection. The term originates from classical studies distinguishing neoteny's rate-based mechanism from timing offsets like paedogenesis, emphasizing causal realism in developmental evolution: somatic retardation preserves adaptive juvenile morphologies under selection pressures favoring early reproduction. Empirical validation comes from comparative ontogenies, where neotenic lineages exhibit extended larval-like phases, quantifiable via allometric scaling of trait sizes against age or size proxies. This definition holds across taxa, from amphibians displaying facultative neoteny under environmental cues to domesticated mammals, underscoring its role in adaptive paedomorphosis without implying uniform juvenilization across all traits. ![Diagram illustrating heterochrony processes including neoteny][float-right] refers to evolutionary changes in the timing, rate, or duration of developmental events, serving as a broad framework encompassing as one specific mechanism. specifically involves a retardation in the rate of somatic development relative to sexual maturation, allowing juvenile morphological traits—such as large heads, short limbs, and reduced —to persist into adulthood without altering the timing of reproductive maturity. This contrasts with progenesis, another process, where somatic development is truncated due to accelerated sexual maturation, resulting in paedomorphic adults that achieve reproductive capability earlier but with incomplete . Paedomorphosis describes the phenotypic outcome of retaining ancestral juvenile traits in descendant adults, achievable through either neoteny or progenesis, but it is not synonymous with neoteny itself. In neoteny, the extended somatic juvenility arises from a slower developmental tempo, as observed in species like the (Ambystoma mexicanum), where is delayed indefinitely while gonadal development proceeds. Progenesis, by comparison, shortens the overall lifespan of developmental phases, often linked to ecological pressures favoring rapid reproduction, such as in certain salamanders where paedomorphic forms mature sexually in larval habitats without somatic advancement. Neoteny must also be differentiated from peramorphosis, the opposing heterochronic category involving extended or accelerated development beyond ancestral adult forms, such as through hypermorphosis (prolonged growth) or (faster somatic rates). While neoteny and related paedomorphic processes reduce morphological by conserving early ontogenetic stages, peramorphic shifts, like those in some mammalian cranial , extend development to produce novel adult traits. These distinctions highlight neoteny's role in evolutionary paedomorphosis via rate hypomorphosis, distinct from truncation-based mechanisms, with empirical support from comparative studies in amphibians showing divergent life-history outcomes: neoteny often sustains longer lifespans, whereas progenesis correlates with abbreviated generation times.

Evolutionary Significance

Neoteny represents a key heterochronic mechanism in , characterized by the prolongation of somatic development relative to reproductive maturation, resulting in paedomorphic adult forms that retain larval or juvenile traits. This process facilitates evolutionary novelty by decoupling morphological maturation from gonadal development, allowing organisms to achieve without completing ontogenetic trajectories that might be maladaptive in specific environments. In s of the genus Ambystoma, for instance, neoteny has evolved independently multiple times, enabling facultative shifts between metamorphic and paedomorphic life histories that enhance in stable aquatic habitats where terrestrial imposes high energetic costs. The adaptive value of neoteny lies in its promotion of developmental plasticity, which can buffer against environmental variability and open novel ecological niches. By retaining traits such as gills or reduced , neotenic forms avoid the risks of , such as or predation during transition, thereby increasing lifetime in predator-poor or resource-limited settings. Empirical studies on Ambystoma demonstrate that neotenic populations often exhibit higher densities in permanent water bodies, with genetic underpinnings involving thyroid hormone signaling pathways that regulate suppression. This plasticity not only sustains populations in marginal habitats but also serves as a precursor for , as isolated neotenic lineages accumulate distinct adaptations over generations. Evolutionarily, neoteny contrasts with peramorphic processes by favoring peramorphosis through retardation rather than acceleration, potentially accelerating diversification rates in lineages prone to . In like beetles, multiple ancient origins of neoteny underscore its recurrent utility in generating morphological disparity via simple shifts in developmental timing, independent of major genomic reorganizations. While neoteny's prevalence across amphibians, , and mammals suggests broad selective advantages—such as enhanced learning capacity or reduced somatic investment—its fixation depends on ecological contexts where juvenile traits confer fitness benefits without compromising . Causal analyses indicate that neoteny thrives in environments with low extrinsic mortality and abundant juvenile resources, aligning with life-history theory predictions for delayed maturation strategies.

Historical Development

Etymology and Early Observations

The term "neoteny" was coined in 1884 by German anatomist Julius Kollmann, derived from the Greek neos ("young") and teinein ("to stretch" or "hold"), denoting the prolongation of juvenile traits into . Kollmann introduced the concept while examining the (Ambystoma mexicanum), a that attains reproductive capability in its larval form, complete with external gills and aquatic adaptations, bypassing typical to a terrestrial adult stage. This observation highlighted neoteny as a distinct heterochronic process, where somatic development lags behind gonadal maturation. Earlier recognition of similar phenomena predated the term, with naturalists documenting persistent larval traits in amphibians. In 1875, interpreted such cases as atavistic reversions to ancestral gill-breathing aquatic forms, suggesting neoteny reflected a return to primitive conditions rather than a novel evolutionary . Observations of neotenic salamanders, including Ambystoma , revealed facultative neoteny, where individuals could metamorphose under certain environmental cues like iodine availability, but often remained paedomorphic in stable aquatic habitats. These findings, primarily from and North American populations, underscored neoteny's prevalence in urodeles, influencing subsequent evolutionary theories on developmental plasticity.

Key Theoretical Contributions

Julius Kollmann coined the term "neoteny" in 1885 to denote the retention of larval or juvenile traits into , particularly as observed in salamanders like the , where aquatic gill-bearing forms reproduce without undergoing to terrestrial adulthood. This concept built on earlier observations of paedogenesis but emphasized the evolutionary potential of delayed somatic maturation relative to reproductive timing. In 1926, Dutch anatomist Louis Bolk advanced neoteny into a broader explanatory framework known as the fetalization or retardation theory, positing that involved a systematic slowing of developmental rates compared to other , resulting in the persistence of fetal characteristics—such as a globular , reduced , and expansion—into adulthood. Bolk argued this retardation affected multiple organ systems, linking neoteny not only to morphology but to extended dependency and plasticity, though later critiques noted inconsistencies in comparing and ontogenies across disparate traits. Julian Huxley refined the theoretical scope of neoteny in 1927 by integrating it into the study of —shifts in developmental timing—as a mechanism of evolutionary change, distinguishing neoteny specifically as the retardation of somatic (body) development while gonadal maturation proceeds on schedule, in contrast to progenesis, where somatic growth is truncated to achieve early with juvenile form. Huxley's framework highlighted how such dissociations could generate paedomorphic adults, providing a quantitative basis for modeling heterochronic evolution beyond qualitative descriptions. Gavin de Beer, in his 1930 book Embryos and Ancestors, synthesized neoteny within a critique of strict , proposing that evolutionary novelties often arise through paedomorphosis via neoteny, where ancestral juvenile stages become fixed in descendant adults, enabling in which different body parts develop at independent rates. De Beer's analysis of embryos demonstrated how neoteny facilitates by preserving plasticity and reducing specialization, influencing subsequent evo-devo research on developmental constraints.

Underlying Mechanisms

Genetic and Molecular Bases

Neoteny arises from genetic alterations that delay or truncate the expression of genes responsible for morphological and physiological traits, often involving regulatory elements that control developmental timing. These changes can manifest as in transcription factors, signaling pathways, or cis-regulatory sequences, leading to prolonged juvenile profiles. In vertebrates, such mechanisms frequently implicate heterochronic shifts in developmental programs, where juvenile states are stabilized through inhibitory feedback loops or reduced sensitivity to maturation signals. In amphibians, particularly the (Ambystoma mexicanum), neoteny is genetically controlled by a single recessive that prevents , resulting in retention of larval gills and aquatic morphology into adulthood. This , dominant in related species like the for inducing , disrupts hormone-mediated signaling, which normally triggers tissue remodeling. Laboratory strains exhibit neoteny due to artificial selection, with genetic analyses revealing high and fixation of neotenic traits independent of wild populations. In mammals, including humans, molecular evidence points to neoteny in neural development through duplications and regulatory evolution. Human-specific paralogs SRGAP2B and SRGAP2C, arising from segmental duplications approximately 2-3 million years ago, inhibit the ancestral SRGAP2A protein, thereby reducing its suppression of SYNGAP1 and prolonging maturation. Proteomic studies across confirm delayed synaptic protein maturation in humans compared to chimpanzees, correlating with extended periods of . Transcriptional analyses further show human retaining fetal-like patterns into postnatal stages, unlike faster-maturing non-human primates. Broader molecular bases include heterochronic shifts in microRNAs or splicing factors that fine-tune timing, as seen in comparative genomic studies of paedomorphic traits. For instance, balancing of splicing regulators is required for synaptic neoteny, where imbalances mimic neurodevelopmental disorders. These mechanisms underscore neoteny's role in evolutionary divergence, though direct causation remains inferred from comparative data rather than experimental recapitulation in most cases.

Developmental and Hormonal Processes

Neoteny arises from heterochronic developmental shifts that retard somatic maturation relative to gonadal development, resulting in the retention of larval or juvenile morphological, physiological, and behavioral traits in reproductively mature individuals. This retardation can be facultative, allowing under certain environmental cues, or obligate, as seen in species like the (Ambystoma mexicanum). In amphibians, hormonal control primarily involves the hypothalamus-pituitary-thyroid (HPT) axis, where insufficient thyroid hormone (TH) signaling maintains neoteny by blocking metamorphosis. Neotenic forms exhibit low endogenous TH titers throughout larval stages, failing to surge as in metamorphic conspecifics, due to defects in hypothalamic corticotropin-releasing hormone (CRH) stimulation of thyrotropin (TSH) or downstream responsiveness. Exogenous administration of TH, such as thyroxine (T4) or triiodothyronine (T3), induces metamorphosis in facultatively neotenic species like the axolotl, confirming functional TH receptors (TRs) but highlighting upstream regulatory failures. Quantitative trait loci (QTL), including met1, modulate TH sensitivity, implicating genes like nradd (involved in neural apoptosis) and pou1f1 (pituitary transcription factor) in neotenic differentiation. Obligate neoteny in urodeles such as Necturus maculosus involves tissue-specific insensitivity to TH despite a functional HPT system, preventing somatic remodeling like gill resorption or limb elongation. induction requires not only TH but also TSH or hypothalamic stimulation, underscoring neoteny as a deviation in endocrine integration rather than TH absence alone. In domesticated mammals, neotenic traits emerge from selection pressures favoring tameness, which retard overall developmental rates and correlate with adrenal hypofunction and lowered stress hormones like . Experimental domestication demonstrates hormonal shifts, including reduced ACTH, contributing to paedomorphic features such as floppy ears and shortened muzzles, though direct TH mediation remains less established than in amphibians. These processes suggest neoteny involves conserved heterochronic mechanisms modulated by endocrine timing, with amphibians providing the clearest hormonal models.

Manifestations in Animals

Neoteny in Amphibians and Aquatic Species

Neoteny in amphibians primarily occurs among (order Urodela), where it manifests as paedomorphosis—the retention of larval traits such as , aquatic locomotion, and a flattened into , bypassing metamorphic transformation to terrestrial forms. This phenomenon is documented in nine of the ten salamander families, often as an alternative life history to . Paedomorphic salamanders exhibit delayed somatic development relative to reproductive maturation, enabling in stable aquatic habitats while avoiding the physiological costs and mortality risks associated with terrestrial transition. The axolotl (Ambystoma mexicanum), endemic to Lake Xochimilco and surrounding waters in central Mexico, represents a prominent example of neoteny, with wild populations predominantly paedomorphic and retaining juvenile features like feathery external gills for branchial respiration, lidless eyes, and permeable skin throughout adulthood. These salamanders reach sexual maturity at lengths of 15–45 cm without endogenous thyroid hormone surges sufficient for metamorphosis, though exogenous thyroxine administration can induce it experimentally, confirming the underlying hormonal mechanism. Neoteny in axolotls is linked to permanent aquatic environments with low predation pressure from large fish, conferring advantages like enhanced regenerative capacity, as evidenced by their ability to regrow limbs, spinal cord, and even parts of the heart and brain. However, habitat degradation has critically endangered wild axolotls, with populations declining over 90% since the 1980s due to pollution and introduced species. Facultative neoteny, where individuals can either metamorphose or remain paedomorphic based on environmental cues, is observed in species like the (Ambystoma tigrinum and related Ambystoma complex), with neotenic forms predominant in high-elevation, fishless lakes where cooler temperatures and resource stability favor larval retention. Evolutionary analyses indicate neoteny evolved multiple times in Ambystoma, often correlating with of isolated aquatic niches at elevations above 2,000 meters, where yields lower fitness due to risks and energy demands. Similarly, the mudpuppy (Necturus maculosus) exhibits paedomorphosis, remaining fully aquatic with gilled larvae-like morphology across its range in eastern North American rivers and lakes. In other amphibian groups, neoteny is rarer; for instance, paedomorphosis in the Ezo salamander (Hynobius retardatus) of involves facultative retention of larval traits in specific pond habitats, documented since observations in the . Among strictly aquatic species beyond , true neoteny is less common, though heterochronic shifts akin to paedomorphosis occur in some lineages, such as delayed maturation in certain cave-adapted populations, but these lack the pronounced larval-adult dissociation seen in salamanders. Overall, amphibian neoteny underscores adaptive plasticity in life cycles, with genetic underpinnings involving pathway genes like thrb and environmental modulation via iodine availability.

Neoteny in Domesticated Mammals

Domesticated mammals frequently display neoteny as part of the , where artificial selection for traits like tameness results in the retention of juvenile morphological, behavioral, and physiological features into adulthood. Common neotenic manifestations include shortened muzzles, floppy ears, reduced , depigmented patches, smaller teeth, and prolonged juvenile playfulness or nonseasonal estrus cycles. These changes arise not from direct selection for morphology but as pleiotropic effects linked to reduced neural crest cell activity during development, which influences craniofacial structure, pigmentation, and adrenal function. The Russian silver fox (Vulpes vulpes) experiment, initiated by Dmitry Belyaev in 1959, provides experimental evidence: foxes selected solely for reduced fear and aggression toward humans over 10-15 generations exhibited neotenic traits such as floppy ears, curled tails, coats, and widened skulls resembling juveniles, with 18-35% of classified as "elite tame" by the fourth generation. This rapid emergence—within 4-6 generations for some traits—demonstrated neoteny as a of tameness selection, with genetic analyses identifying QTLs associated with both and morphology. In dogs (Canis familiaris), neoteny is evident when compared to ancestral wolves (Canis lupus). Zoologist Desmond Morris observed in his 1969 book The Human Zoo that domesticated dogs are "rather juvenile versions of their wild counterparts," highlighting the retention of juvenile traits such as prolonged dependency and playfulness into adulthood, in contrast to adult wolves. Adult dogs retain pup-like proportions, including larger crania relative to body size, shorter snouts, pronounced forehead stops, and softer facial features that enhance expressiveness, diverging from wolves' more robust adult morphology. Brain size reduction averages 10-15% in dogs versus wolves, correlating with juvenile-like docility. Similar patterns occur in domesticated cats (Felis catus), with smaller brains (about 25% reduction from wildcats) and juvenile facial rounding; guinea pigs (Cavia porcellus), showing prolonged infancy and reduced aggression; and pigs (Sus domesticus), featuring floppy ears and curly tails absent in wild boars. Rats (Rattus norvegicus) selected for tameness likewise display neotenic white spotting and behavioral juvenility.
  • Morphological traits: Floppy ears (dogs, foxes, pigs), shortened muzzles (dogs, cats, foxes), (foxes, dogs, rats).
  • Behavioral traits: Extended playfulness and reduced (foxes, dogs, rats).
  • Physiological traits: Smaller adrenal glands and nonseasonal (multiple ).
While these neotenic shifts enhance adaptability to human environments, they may confer costs like to predators in feral populations, underscoring the trade-offs of . Recent genomic studies confirm shared genetic underpinnings across , such as variants in neural crest-related genes, supporting neoteny's role in syndrome covariation.

Neoteny in Wild Mammals and Other Taxa

In wild mammals, neoteny manifests prominently in the (Heterocephalus glaber), a eusocial subterranean native to arid regions of , where adults retain juvenile-like developmental patterns contributing to exceptional exceeding 30 years despite a small body size of approximately 35-40 grams. This species exhibits delayed somatic maturation, with processes such as hematopoiesis mirroring embryonic or juvenile states in other ; for instance, occurs in both and , an extramedullary site predominant in fetal mammals but atypical in adults. Neotenic features extend to neural development, where maturation proceeds slowly, preserving plasticity and correlating with resistance to age-related pathologies like neurodegeneration. These traits are hypothesized to underpin the naked mole-rat's cancer resistance, hypoxia tolerance, and , adaptations suited to its colony-based, low-oxygen burrow environment where reproduction is restricted to few breeders, reducing selection pressure for rapid aging. Unlike domesticated mammals, where neoteny often arises from artificial selection for tameness, the naked mole-rat's neoteny appears evolutionarily conserved, linked to in highly cooperative species, as evidenced by comparative genomic analyses showing retained juvenile profiles into adulthood. Examples of neoteny in wild non-mammalian taxa beyond amphibians are scarce and typically facultative rather than . In certain reptilian lineages, such as some blind cave-dwelling species, paedomorphic traits like retained larval pigmentation or reduced occur sporadically under environmental stress, but these do not constitute full neoteny as defined by retarded somatic development with reproductive maturity. Avian taxa show no well-documented neoteny in wild populations, though some flightless island endemics display paedomorphosis in skeletal proportions, potentially as a byproduct of rather than heterochronic shifts. Overall, neoteny in wild taxa outside social mammals and amphibians remains underexplored, with most empirical data emphasizing its role in niche adaptations like extended juvenility for ecological persistence.

Neoteny in Human Biology and Evolution

Anatomical and Morphological Evidence

Humans retain several cranial features characteristic of juvenile great apes, including a globular skull shape, thin cranial vault bones, and a reduced supraorbital torus or brow ridge. These traits contrast with the more prognathic, robust skulls of adult chimpanzees and gorillas, where facial projection and supraorbital development increase markedly during ontogeny. Morphometric analyses of fossil hominins show a progressive reduction in facial prognathism and midfacial retraction in Homo sapiens compared to earlier species like Homo erectus, aligning adult human profiles more closely with juvenile australopithecine or ape forms. The human face exhibits paedomorphic proportions, such as a broadened, flattened midface with vertically shortened dimensions, large relative eye orbits, and reduced nasal and maxillary prominence—features that persist into adulthood unlike in other , where somatic maturation elongates and projects the face. Dental evidence supports this, with smaller, less robust and delayed eruption patterns resembling those of immature , though absolute size reduction may reflect dietary shifts rather than pure heterochronic retardation. Skeletal morphology further indicates neotenic retention, including a gracile postcranial with reduced muscle attachments, elongated limbs relative to trunk length (particularly longer legs than arms), and an absence of structures like the present in adult male . Comparative ontogenetic studies reveal that while shape changes mimic paedomorphosis through retarded growth trajectories in and cranial elements, braincase expansion involves peramorphic extension, achieving larger absolute volumes than ancestral juveniles. This dissociation—retardation in somatic traits alongside extension in neural ones—underlies claims of neoteny in , though critics argue it represents mosaic rather than uniform juvenilization.

Behavioral and Cognitive Correlates

Neotenic morphological features in adult humans, such as relatively large eyes, small noses, and rounded faces, serve as cues that psychologically trigger protective instincts, affection, and attraction, distinct from the biological process of neoteny itself but rooted in evolutionary adaptations for caregiving. This phenomenon, known as the baby schema or Kindchenschema, was conceptualized by Konrad Lorenz as a set of infantile traits that elicit nurturing responses, promoting social bonding and similar to reactions observed toward juveniles in other species like kittens or puppies. neoteny manifests behaviorally through the retention of juvenile traits such as prolonged playfulness and exploratory tendencies into adulthood, distinguishing from other where such behaviors diminish sharply post-infancy. Adult engage in play at rates exceeding those of adult great apes, facilitating social bonding, , and the rehearsal of complex skills, with observed across cultures as a mechanism for physical and emotional . This extension correlates with neoteny's role in promoting affiliative and social structures, as evidenced by comparative studies showing reduced adult play in species with shorter developmental windows. Cognitively, neoteny supports extended periods of neural plasticity and delayed maturation, enabling cumulative learning and abstract reasoning beyond what is typical in other mammals. Synaptic density in human peaks between ages 8 and 10—60% higher than adult levels in visual areas and 50% in frontal regions—far later than in macaques, where peaks occur by 2–4 months, allowing prolonged and refinement into the third decade. This delay fosters enhanced , , and , with transcriptional profiles revealing that 38% of analyzed genes in humans exhibit neotenic expression patterns, particularly in , compared to chimpanzees. Empirical comparative data underscore these correlates: species with longer juvenile phases, including s, show superior performance in problem-solving and social learning tasks, with human rearing periods extending through safe, iterative exploration akin to juvenile states in other taxa. Such traits likely contributed to human evolutionary success by amplifying adaptability, though they remain subject to environmental modulation, as seen in studies of adversity delaying prefrontal-amygdala connectivity maturation beyond typical timelines.

Empirical Measurements and Comparative Data

Empirical assessments of neoteny in humans often quantify craniofacial morphology through geometric and ontogenetic scaling. Comparative studies of development reveal that adult crania retain proportions resembling juvenile great apes, with reduced facial and a relatively larger . For instance, in chimpanzees (Pan troglodytes), postnatal facial growth extends the muzzle forward, resulting in adult facial length comprising approximately 50-60% of total cranial length, whereas in humans, this ratio stabilizes earlier at around 30-40%, preserving a more globular, infantile vault shape. Landmark-based analyses confirm that human adults occupy a distinct morphospace, offset from adult apes toward their juvenile forms along allometric trajectories, with shape differences emerging early in due to divergent growth rates in the viscerocranium. Brain size metrics further support neotenic patterns, as humans exhibit prolonged postnatal encephalization. At birth, human brain volume averages 350-400 cm³, representing less than 25% of adult size (≈1,350 cm³), the lowest relative value among primates; chimpanzees achieve ≈30-40% at birth (adult ≈400 cm³). This delay correlates with extended cortical folding and gyrification, where human prefrontal regions mature over 20-25 years, compared to 10-15 years in apes. Molecular data provide transcriptional evidence of neoteny, particularly in . Analysis of 7,958 genes across s, chimpanzees, and rhesus macaques identified 299 heterochronic shifts among 3,075 comparable transcripts, with 38% (114 genes) indicating human neoteny—wherein adult profiles resemble juvenile chimpanzee states more closely than adult chimpanzee ones (FDR=10%, P=2×10⁻⁴). These neotenic genes, affecting ≈4% of the cortical transcriptome, enrich in gray matter regions and peak in divergence around age 10, underscoring slower maturation in s relative to apes.
FeatureHuman AdultChimpanzee AdultJuvenile Ape Similarity to Human Adult
Relative Brain Size at Birth (% adult)<25%≈30-40%N/A
Facial Length/Cranial Length Ratio30-40%50-60%High (retains infantile proportions)
Heterochronic Genes (Neoteny %)38% of shiftsBaseline (0% reference)Adult human ≈ juvenile chimp
</section_text>

Controversies and Critiques

Debates on Human Neoteny

The hypothesis of pronounced neoteny in humans, involving the retention of juvenile primate traits into adulthood through developmental retardation, has been central to discussions of hominid evolution since Louis Bolk's early 20th-century fetalization theory and Stephen Jay Gould's 1977 emphasis on heterochrony in Ontogeny and Phylogeny. Proponents argue this paedomorphosis—specifically neoteny via slowed somatic maturation relative to neural growth—explains traits like reduced facial prognathism, larger relative brain size, and prolonged behavioral plasticity, facilitating cognitive advancements. Empirical morphometric data supports facial paedomorphosis in Homo compared to great apes, with studies showing negative allometry in the splanchnocranium (face) alongside positive scaling in the neurocranium (braincase), correlating with increased encephalization and inferred cognitive capacity. Critics, however, contend that neoteny oversimplifies evolutionary , as the lineage exhibits a mosaic of paedomorphic and peramorphic (growth-extending) processes rather than uniform retardation. Barry Shea (1989) argued that while prolongs growth duration, this does not necessitate the dissociation of neural from somatic rates implied by strict neoteny; chimpanzee-like juvenile features are not simply "frozen" but modified through rate hypomorphosis and extension in specific modules, such as expansion via peramorphosis. Morphometric analyses confirm this hybrid pattern: display coordinated ontogenetic scaling with lateral transpositions yielding paedomorphic facial reduction but hypermorphic volumes exceeding ancestral adults, challenging Gould's retardation model as insufficiently granular. Further critiques highlight biological misapplications, particularly for locomotor adaptations; neoteny doctrine erroneously attributes bipedal traits (e.g., sigmoidal vertebral column, pelvic reorientation) to fetal retention, yet comparative reveals these emerge postnatally in s and are absent in anthropoid embryos, indicating novel rather than paedomorphosis. This misunderstanding risks by underemphasizing socio-cultural and ecological drivers in human phylogeny, as erect posture evolves through geohistorical selection independent of juvenile retention. Behavioral neoteny—extended play, learning periods, and —faces similar scrutiny, with evidence suggesting adaptive prolongation of rather than true neoteny, as adult human integrates extended maturation without reverting to prepubertal states. Recent integrations with hypotheses revive neoteny debates by linking paedomorphic traits (e.g., reduced , neotenic facial cues) to selection for , but empirical genetic and data remain contested, with critics noting insufficient causal links between and behavioral syndromes akin to domesticated animals. Overall, while neoteny illuminates select human traits, debates underscore the need for multifaceted heterochronic models over monocausal explanations.

Challenges in Domestication Syndrome Explanations

One prominent explanation for the —a cluster of traits including neotenous features like retained juvenile morphology, smaller skulls, and larger relative eye size in adults—posits mild deficits in cell (NCC) development during embryogenesis, leading to pleiotropic effects on multiple tissues. This hypothesis, articulated in 2014, suggests that selection for reduced inadvertently disrupts NCC migration and proliferation, which contribute to craniofacial structures, pigmentation, adrenal glands, and other syndrome-associated elements. However, empirical support remains indirect, relying on correlations rather than causal demonstrations, such as genomic signatures of selection on NCC-related genes without confirming their role in trait origins. A core challenge lies in the syndrome's lack of universality across domesticated taxa, undermining unified mechanistic accounts. Traits purportedly linked to NCC deficits, including neotenous paedomorphosis (e.g., shortened snouts and globular skulls), floppy ears, and , appear inconsistently; for instance, domesticated pigs and chickens exhibit increased relative contrary to expected reductions, while sheep and ducks show no such decrease. Similarly, neotenous behavioral retention, such as prolonged playfulness, varies widely and does not align predictably with morphological changes. Analyses of over 200 domesticated breeds indicate only a small core of shared traits (e.g., tameness and docility), with peripherals like curly tails or white spotting absent in many lineages, suggesting correlated via linkage or independent selection rather than a singular pleiotropic pathway. Experimental models, such as Belyaev's silver fox from onward, face scrutiny for overstating tameness as the causal driver. Many syndrome traits, including and skeletal modifications akin to neoteny, pre-existed in the farmed founder populations before for friendliness, as evidenced by comparisons with pre- farm foxes and wild counterparts. In rats domesticated over 25 generations without explicit tameness criteria, similar pigmentation and vertebral changes emerged, pointing to broader factors like regimes. Alternatives, such as endocrine disruptions from Belyaev's 1979 or shared reproductive perturbations (e.g., altered breeding and male selection biases), better account for specific traits like spotting without invoking NCC universality. For neoteny specifically, explanations invoking systemic —delayed maturation across traits—struggle against evidence of modular developmental shifts, where juvenile retention in morphology does not consistently extend to or across . Genomic surveys reveal polygenic architectures for individual traits, challenging the notion of a master regulator like NCC deficits producing coordinated paedomorphosis; instead, likely amplifies pre-existing standing variation through relaxed and human preferences, yielding variable outcomes. These inconsistencies highlight the need for species-specific causal tests, as overarching models risk conflating with mechanism.

Methodological and Interpretive Issues

One persistent methodological challenge in neoteny research stems from the imprecise demarcation between neoteny—a specific heterochronic process involving the retardation of somatic developmental rates while maintaining ancestral maturation timing—and the broader category of paedomorphosis, which encompasses outcomes like progenesis (accelerated reproductive maturation with truncated somatic growth). This conflation, evident in early evolutionary literature, complicates the identification of true neoteny versus other paedomorphic mechanisms, as ancestral juvenile traits can be retained through multiple heterochronic pathways without invoking rate hypomorphosis. Quantifying neoteny demands high-resolution ontogenetic data to compare developmental trajectories across taxa or lineages, yet such data are often scarce, particularly for fossil records where intermediate stages are absent, hindering accurate reconstruction of ancestral timing and rates. Distinguishing pure rate changes (hallmark of neoteny) from phase shifts or size-related offsets proves notoriously difficult without complete serial sampling, as acknowledged in paleobiological analyses; for instance, detailed embryonic or larval sequences are rarely preserved, leading to reliance on proxy metrics like allometric slopes. Traditional allometric methods exacerbate this, as divergent heterochronic processes can generate convergent growth patterns, yielding flawed inferences about underlying mechanisms; multivariate approaches introduce "dimensionality bias," where high-dimensional shape data obscure specific heterochronic modes. Interpretively, neoteny's evolutionary role is often overstated without robust causal evidence, as correlations between juvenile trait retention and adaptations (e.g., in metamorphosis or mammalian ) do not confirm neoteny as the driver rather than a pleiotropic byproduct of selection on correlated traits like derivatives. In , claims of pervasive neoteny—popularized by figures like —face critique for neglecting peramorphic elements, such as hypermorphic expansion and steeper allometric slopes in cranial traits, resulting in rather than uniform paedomorphosis; human growth rates are not globally retarded, undermining the hypothesis's coherence. These interpretive pitfalls are compounded by potential anthropocentric biases in source selection, where academic narratives favoring as a master process may undervalue alternative explanations like independent trait or environmental plasticity. Emerging comparative and event-pairing protocols offer partial remedies by integrating geometric with phylogenetic frameworks to detect signals more reliably, yet they still grapple with equifinality—where similar adult morphologies arise from disparate developmental shifts—and require validation against molecular timing data. In domesticated taxa, interpretive issues arise from conflating neotenous morphology with cognitive or behavioral outcomes, as meta-analyses reveal no consistent domestication-induced cognitive deficits despite paedomorphic appearances, suggesting interpretive overreach in linking neoteny to "dumbed-down" phenotypes. Overall, these challenges underscore the need for multidisciplinary integration of genomic, , and experimental data to disentangle neoteny's contributions from confounding .

Recent Advances and Future Directions

Genomic and Subcellular Insights

, the evolutionary alteration in the timing or rate of developmental events, underpins neoteny at the genomic level through changes in regulatory elements controlling timing. Recent studies highlight shifts in regulation, such as prolonged expression of miR156 in neotenic plant species like , which delays vegetative phase transitions without abolishing adult traits, suggesting conserved mechanisms across taxa for retaining juvenile forms via heterochronic timing adjustments. In animals, genomic sequencing of neotenic salamanders in the Ambystoma complex reveals evolutionary signatures in large genomes, including expansions in transposable elements and gene families linked to developmental retardation, enabling facultative neoteny as a reproductive strategy. At the subcellular level, proteomic analyses of synaptic development demonstrate neoteny in human neocortical synapses, where postsynaptic density maturation proceeds 2-3 times slower than in macaques or mice, retaining juvenile profiles into adolescence due to elevated Rho guanine nucleotide exchange factors (RhoGEFs) that prolong perinatal plasticity phases. This extended synaptic neoteny correlates with enhanced cognitive flexibility, as evidenced by delayed proteome shifts in human prefrontal cortex samples analyzed via mass spectrometry across species and developmental stages. Xenotransplantation experiments further confirm that human cortical pyramidal neurons maintain a prolonged neotenic timescale even in the faster-developing mouse environment, dependent on species-specific extracellular matrix and inhibitory interactions between proteins like SRGAP2 and SYNGAP1. Transcriptomic data reinforce these findings, showing human brain gene expression patterns exhibit neoteny, with significant postnatal changes delayed relative to chimpanzees, particularly in , enriching for genes involved in neural growth and enriched in gray matter. These molecular delays likely contribute to extended neurodevelopmental windows, though they also associate with vulnerabilities in disorders like via prolonged plasticity. Overall, integrating genomic, proteomic, and cellular data points to regulatory in timing genes and pathways as key to neotenic , with human-specific variants in developmental regulators emerging from comparative sequencing of hominins and .

Ecological and Experimental Studies

Ecological studies have identified associations between neoteny and specific environmental conditions in populations. In mole s of the Ambystoma, neoteny evolves preferentially in occupying habitats with lower diversity, such as permanent aquatic ponds, where facultative neoteny allows reproductive maturity without under stable conditions. Analysis of 19 Ambystoma revealed that transitions to neoteny occur at rates comparable to reversals, suggesting a "goldilocks zone" of favoring retention of larval traits. Similarly, s with larger genomes are predominantly found in permanent aquatic habitats, linking paedomorphosis to reduced terrestrial pressures. In introduced populations of paedomorphic newts, such as Lissotriton vulgaris, neoteny persists due to novel gene-environment interactions in altered habitats. Experimental manipulations in laboratory settings have elucidated mechanisms underlying neoteny, particularly in urodele amphibians like the (Ambystoma mexicanum). Exposure to exogenous , such as thyroxine, induces in neotenic axolotls, overriding genetic predispositions for paedomorphosis and resulting in resorption and terrestrial adaptations. A 2018 study demonstrated that induced metamorphosis restructures bacterial communities in axolotl organs, highlighting microbial influences on developmental transitions. Comparative experiments between neotenic axolotls and metamorphic tiger salamanders (Ambystoma tigrinum) show differences in limb regeneration capacity, with neotenic forms exhibiting superior regenerative potential tied to prolonged larval states. Recent 2025 investigations revealed increased neuronal and glial complexity in metamorphic axolotl brains compared to neotenic counterparts, suggesting neoteny constrains neural maturation. Environmental stressors in controlled experiments promote retention of juvenile traits, supporting adaptive hypotheses for neoteny. A 2025 study found that delays in amphibians, enhancing survival in unstable aquatic environments by preserving regenerative abilities. These findings underscore neoteny's role in balancing reproductive timing with ecological pressures, with ongoing research exploring genomic underpinnings in wild-derived populations.

References

  1. https://anthropogeny.sdsc.edu/moca/topics/neoteny-biological
  2. https://pages.uoregon.edu/titus/herp_old/neoteny.htm
  3. https://pmc.ncbi.nlm.nih.gov/articles/PMC10999947/
  4. https://pmc.ncbi.nlm.nih.gov/articles/PMC2659716/
  5. https://carta.anthropogeny.org/moca/topics/neoteny-biological
  6. https://www.pnas.org/doi/10.1073/pnas.0811620106
  7. https://evolution-outreach.biomedcentral.com/articles/10.1007/s12052-012-0420-3
  8. https://royalsocietypublishing.org/doi/10.1098/rspb.2000.1168
  9. https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2435.13708
  10. https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.01349/full
  11. https://pmc.ncbi.nlm.nih.gov/articles/PMC1690691/
  12. https://pmc.ncbi.nlm.nih.gov/articles/PMC2596372/
  13. https://www.etymonline.com/word/neoteny
  14. https://www.alphadictionary.com/goodword/word/neoteny
  15. https://www.biologydiscussion.com/zoology/amphibians/neoteny-history-factors-and-significance-amphibians/40967
  16. https://pubmed.ncbi.nlm.nih.gov/10423830/
  17. http://www.ludus-vitalis.org/ojs/index.php/ludus/article/viewFile/116/115
  18. https://royalsocietypublishing.org/doi/10.1098/rstb.2022.0078
  19. https://www.pnas.org/doi/10.1073/pnas.2510697122
  20. https://bioone.org/journals/zoological-science/volume-13/issue-6/zsj.13.765/Heterochrony-and-Neotenic-Salamanders--Possible-Clues-for-Understanding-the/10.2108/zsj.13.765.full
  21. https://pmc.ncbi.nlm.nih.gov/articles/PMC9536427/
  22. https://www.cell.com/neuron/fulltext/S0896-6273(24)00645-7
  23. https://pmc.ncbi.nlm.nih.gov/articles/PMC10576238/
  24. https://www.biorxiv.org/content/10.1101/2023.03.01.530630v1.full.pdf
  25. https://www.nature.com/articles/s41576-022-00568-4
  26. https://www.frontiersin.org/journals/endocrinology/articles/10.3389/fendo.2019.00237/full
  27. https://pubmed.ncbi.nlm.nih.gov/14576183/
  28. https://pubmed.ncbi.nlm.nih.gov/8877439/
  29. https://pmc.ncbi.nlm.nih.gov/articles/PMC4096361/
  30. https://link.springer.com/article/10.1023/B:RUGE.0000033312.92773.c1
  31. https://www.sciencedirect.com/science/article/abs/pii/S0031938417304304
  32. https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/dvdy.479
  33. https://www.journals.uchicago.edu/doi/10.1086/418540
  34. https://academic.oup.com/endo/article/145/2/760/2500402
  35. https://www.sciencedirect.com/science/article/abs/pii/S0016648085710313
  36. https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/dvdy.520
  37. https://zoologicalletters.biomedcentral.com/articles/10.1186/s40851-021-00183-x
  38. https://www.sciencedirect.com/science/article/pii/S2589004220304533
  39. https://evolution-outreach.biomedcentral.com/articles/10.1186/s12052-018-0090-x
  40. https://pmc.ncbi.nlm.nih.gov/articles/PMC2763232/
  41. https://www.pbs.org/wnet/nature/dogs-that-changed-the-world-photo-essay-from-wolf-to-dog/1278/
  42. https://pmc.ncbi.nlm.nih.gov/articles/PMC8836321/
  43. https://journals.physiology.org/doi/10.1152/physrev.00040.2015
  44. https://www.embopress.org/doi/10.15252/embj.2021109694
  45. https://www.buckinstitute.org/blog/naked-mole-rats-live-slow-die-old/
  46. https://pubmed.ncbi.nlm.nih.gov/28202600/
  47. https://www.izw-berlin.de/en/the-naked-mole-rat-an-alternative-model-species-for-biomedical-ageing-research.html
  48. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/neoteny
  49. https://pubmed.ncbi.nlm.nih.gov/11953945/
  50. https://pmc.ncbi.nlm.nih.gov/articles/PMC122156/
  51. https://onlinelibrary.wiley.com/doi/abs/10.1002/ajpa.1330320505
  52. https://worldofpaleoanthropology.org/2024/02/13/baby-faces-how-neoteny-affected-our-evolution-guest-post-by-mekhi/
  53. https://pmc.ncbi.nlm.nih.gov/articles/PMC4782005/
  54. https://stanford.edu/~knutson/ans/ansch15.pdf
  55. http://www.ijhssnet.com/journals/Vol_5_No_2_February_2015/4.pdf
  56. https://www.sciencedirect.com/science/article/am/pii/S0149763423000933
  57. https://pmc.ncbi.nlm.nih.gov/articles/PMC11852096/
  58. https://pmc.ncbi.nlm.nih.gov/articles/PMC6935437/
  59. https://www.acesin.letras.ufrj.br/uploads/2/7/1/1/27113691/neoteny.pdf
  60. http://www.filogenetica.org/cursos/deluna/morfometria/antropologicas/humanchimp.pdf
  61. https://www.sciencedirect.com/science/article/abs/pii/S0047248404000521
  62. https://www.researchgate.net/publication/8522734_Comparison_of_Cranial_Ontogenetic_Trajectories_Among_Great_Apes_and_Humans
  63. https://www.nature.com/articles/s41559-023-02253-z
  64. https://www.pathwayz.org/Tree/Plain/APE%2BVS.%2BHOMININ%2BSKULLS
  65. https://www.pnas.org/doi/10.1073/pnas.0900544106
  66. https://pmc.ncbi.nlm.nih.gov/articles/PMC9420405/
  67. https://www.jstage.jst.go.jp/article/agcjchikyukagaku/45/1/45_KJ00005307043/_article/-char/en
  68. https://pmc.ncbi.nlm.nih.gov/articles/PMC8633120/
  69. https://www.sciencedirect.com/science/article/pii/S0149763423003767
  70. https://www.cell.com/trends/ecology-evolution/abstract/S0169-5347%2820%2930224-X
  71. https://royalsocietypublishing.org/doi/10.1098/rspb.2022.2464
  72. https://www.sciencedirect.com/science/article/pii/S0169534719303027
  73. https://www.researchgate.net/publication/296857923_Paedomorphosis_neoteny_and_evolution
  74. https://www.cambridge.org/core/journals/paleobiology/article/new-method-for-quantifying-heterochrony-in-evolutionary-lineages/83D03C714E53A22BDB5FAE894617C462
  75. http://jameslamsdell.com/s/Lamsdell-2021-A-new-method-for-quantifying-heterochrony.pdf
  76. https://www.sciencedirect.com/science/article/pii/S0022519385700045
  77. https://geosci.uchicago.edu/~mwebster/Webster_and_Zelditch_2005.pdf
  78. https://pubmed.ncbi.nlm.nih.gov/8928718/
  79. https://pmc.ncbi.nlm.nih.gov/articles/PMC10658192/
  80. https://bioone.org/journals/paleobiology/volume-47/issue-2/pab.2020.17/A-new-method-for-quantifying-heterochrony-in-evolutionary-lineages/10.1017/pab.2020.17.full
  81. https://www.swansea.ac.uk/press-office/news-events/news/2024/05/a-neverland-for-salamanders-researchers-discover-neoteny-goldilocks-zone.php
  82. https://pmc.ncbi.nlm.nih.gov/articles/PMC6784731/
  83. https://neobiota.pensoft.net/article/152115/
  84. https://earth.org/?endangered-species=axolotl-endangered-species-spotlight
  85. https://www.nature.com/articles/s41598-018-29373-y
  86. https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.70060
  87. https://pmc.ncbi.nlm.nih.gov/articles/PMC11923732/
  88. https://www.sciencedirect.com/science/article/pii/S2589004225013392
Add your contribution
Related Hubs
Contribute something
User Avatar
No comments yet.