Neoteny ( /niːˈɒtɨniː/), also called juvenilization [2], is one of the two ways by which paedomorphism can arise. Paedomorphism is the retention by adults of traits previously seen only in juveniles, and is a subject studied in the field of developmental biology. In neoteny, the physiological (or somatic) development of an animal or organism is slowed or delayed. In contrast, in progenesis, sexual development occurs faster. Both processes result in paedomorphism.[3] 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.[4]
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).[5]
The word neoteny is borrowed from the German Neotenie, the latter constructed from the Greek νέος (neos, young) and τείνειν (teínein, tend to). The adjectivial form of the word is either "neotenous" or "neotenic".[6] The opposite of neoteny is either called "gerontomorphic"[7] or "peramorphic"[8].
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These are neotenous traits in humans: flattened face, [2] broadened face,[9] large brain,[2] hairless body,[2] hairless face,[10] small nose,[10] reduction of brow ridge,[2] small teeth,[2] small upper jaw (maxilla),[2] small lower jaw (mandible),[2] thinness of skull bones,[9] limbs proportionately short compared to torso length,[9] longer leg than arm length,[11] larger eyes,[12] and upright stance.[13] [7]
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".[14] 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."[2]
Delbert D. Thiessen claimed that "neoteny becomes more apparent as early primates evolved into later forms" and that primates have been "evolving toward flat face."[15] Stephen Jay Gould argued "that the whole enterprise of ranking groups by degree of neoteny is fundamentally unjustified." (Gould, 1996, pg. 150).[16]
In opposition, others believe neoteny has been the main cause of human evolution, because humans only retain some juvenile traits while relinquishing others.[17] For instance, the high leg-to-body ratio (long legs) of adult humans as opposed to human infants shows that there is not holistic trend in humans towards neoteny when compared to the other Great Apes.[17] [18]
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.[7] Brian Keith Hall also cites the long legs of humans as a peramorphic trait in sharp contrast to neoteny.[8]
Of course, an all or nothing approach is pointless, a combination of heterochronic processes is more likely and more reasonable (Vrba, 1996).
Ashley Montagu notes the following neotenous traits in women relative to men: more delicate skeleton, smoother ligament attachments, smaller mastoid processes, reduced brow ridges, more forward tilt of the head, narrower joints, less hairy, more delicate skin, 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 tearducts.[2]
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.[19] Michael R. Cunningham found, using a panel of "Asian", "Hispanic" and "White" judges, 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"[20] and his study led him to conclude that "large eyes" were the most "effective" of the "neonate cues".[20] Cunningham also said that "shiny" hair may be indicative of "neonate vitality".[20]
Cunningham noted a "difference" in the preferences of Asian and White judges with Asian judges preferring women with "less mature faces" and smaller mouths than the White judges.[20] Cunningham hypothesized that this difference in preference may stem from "ethnocentrism" since "Asian faces possess those qualities", so Cunningham re-analyzed the data with "11 Asian targets excluded" and concluded that "ethnocentrism was not a primary determinant of Asian preferences."[20] Using a panel of "Blacks" and "Whites" as judges, Cunningham found more neotenous faces were perceived as having both higher "femininity" and "sociability".[20]
In contrast, Cunningham found that faces that were "low in neoteny" were judged as "intimidating".[20] 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".[20] In a study of Italian women who have won beauty competitions, it was found that the Italian women who won the beauty competitions had faces characterized by more "babyness" traits compared to the "normal" women used as a reference.[21] In a study of 60 Caucasian female faces, the average facial composite of the 15 faces found most attractive differed from the facial composite of the whole by: a reduced lower facial region, a thinner jaw and a higher forehead.[22]
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, "Orientals", not whites, are "clearly" the most neotenized human race.[16]
Ashley Montagu mirrored this statement when he stated that the "Mongoloid skull, whether Chinese or Japanese" is the most neotenized human skull.[2] Ashley Montagu further claimed 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.[2] Ashley Montagu claimed that humans have more neotenized skulls than Australopithecus.[23]
Delbert D. Thiessen claimed that Homo Sapiens are more neotenized than Homo Erectus, Homo Erectus was more neotenized than Australopithicus, Great Apes are more neotenized than Old World monkeys and Old World monkeys are more neotenized than New World monkeys.[15]
Nancy Lynn Barrickman claimed Brian T. Shea found 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.[24] Ashley Montagu believed that part of the differences seen in the morphology of "modernlike types of man" can be attributed to different rates of "neotenous mutations" in their early populations.[25]
According to Ashley Montagu "The Mongoloid skull has proceeded further than in any other people."[2] "The Mongoloid skull, whether Chinese or Japanese, has been rather more neotenized than the Caucasoid or European."[2] "The female skull, it will be noted, is more pedomorphic in all human populations than the male skull."[2]
In Ashley 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".[2]
According to Clive Bromhall "Mongoloid races are explained in terms of being the most extreme pedomorphic humans."[26]
Richard Grossinger claimed "The intuition that advanced human development was pedomorphic rather than recapitulationary and accelerated was disturbing to many Eurocentric nineteenth century anthropologists."[27] "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."[27]
Stephen Oppenheimer claimed "An interesting hypothesis put forward by paleontologist Stephen Jay Gould many years ago was that the package of the Mongoloid anatomical changes could be explained by the phenomenon of neoteny, whereby an infantile or childlike body form is preserved in adult life. 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."[28] "[D]ecrease unnecessary muscle bulk, less tooth mass, thinner bones and smaller physical size; ...this follows the selective adaptive model of Mongoloid evolution."[28]
According to Ashley Montagu, Bushmen have the following neotenous traits relative to Caucasoids: "large brain", light skin pigment, less hairy, round-headed, bulging forehead, small cranial sinuses, flat roof of the nose, small face, small mastoid processes, wide eye separation, median eye fold, short stature and horizontal penis.[2]
According to Ashley Montagu, 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.[2]
Humans have been evolving toward greater "psychological-neoteny".[29] Highly-educated people and eminent scientists usually demonstrate more neotenous psychological traits,[30] and students with more of a "baby face" tend to "outperform" their less-neotenized peers in school.[31] In fact, the ability of an adult human to learn has long been considered a neotenous trait.[32] Physical neotenization in humans has, likewise, caused psychologically neotenous traits in humans: curiosity, playfulness, affection, sociality and an innate desire to cooperate.[33]
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. [34]
Down syndrome neotenizes the brain and body to the fetal state.[35] Down syndrome is characterized by decelerated maturation (neoteny), incomplete morphogenesis (vestigia) and atavisms.[36] Dr. Weihs considers Down syndrome to be a condition of "neoteny" that makes people "like a baby."[37]
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".[37]
Dr. Thomas Lamarre, professor of East Asian Studies and Art History at McGill University, claimed that after World War II Japanese people as shown in their manga (漫画) and anime (アニメ) became "fascinated" with "neoteny" and "cuteness".[38]
Domestication has involved selection for behavioral characteristics that characterize young animals so, since "behavior is rooted in biology", domestication has resulted in an array of similar neotenous physical traits having arisen in various domesticated animals.[41] Such neotenous physical traits in domesticated animals such as dogs, pigs, cats, and recently foxes are floppy ears, changes in reproductive cycle, curly tails, piebald coloration, fewer or shortened vertebra,[41] large eyes, rounded forehead, large ears and shortened muzzle.[42]