Neoteny

Neoteny (/niˈɒtəni/), also called juvenilization, is the delaying or slowing of the physiological (or somatic) development of an organism, typically an animal. Neoteny is found in modern humans. In progenesis (also called paedogenesis), sexual development is accelerated. Neoteny (/niˈɒtəni/), also called juvenilization, is the delaying or slowing of the physiological (or somatic) development of an organism, typically an animal. Neoteny is found in modern humans. In progenesis (also called paedogenesis), sexual development is accelerated. Both neoteny and progenesis result in paedomorphism (or paedomorphosis), a type of heterochrony. Some authors define paedomorphism as the retention of larval traits, as seen in salamanders. Both neoteny and progenesis cause the retention in adults of traits previously seen only in the young. Such retention is important in evolutionary biology, domestication and evolutionary developmental biology. The origins of the concept of neoteny have been traced to the Bible (as argued by Ashley Montagu) and to the poet William Wordsworth's 'The Child is the father of the Man' (as argued by Barry Bogin). The term itself was invented in 1885 by Julius Kollmann as he described the axolotl's maturation while remaining in a tadpole-like aquatic stage complete with gills, unlike other adult amphibians like frogs and toads. 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'. For the opposite of 'neotenic', different authorities use either 'gerontomorphic' or 'peramorphic'. 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)'. In 1926 Louis Bolk described neoteny as the major process in humanization. In his 1977 book Ontogeny and Phylogeny, Stephen Jay Gould noted that Bolk's account constituted an attempted justification for 'scientific' racism and sexism, but acknowledged that Bolk had been right in the core idea that humans differ from other primates in becoming sexually mature in an infantile stage of body development. 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 and legs. 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. However, humans also have relatively large noses and long legs, both peramorphic (not neotenic) traits. Some evolutionary theorists have proposed that neoteny was a key feature in human evolution. Gould argued that the 'evolutionary story' of humans is one where we have been 'retaining to adulthood the originally juvenile features of our ancestors'. 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.' 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.' However, in light of some groups using neotony-based arguments to support racism, Gould also argued 'that the whole enterprise of ranking groups by degree of neoteny is fundamentally unjustified' (Gould, 1996, pg. 150). 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. Neoteny is seen in domesticated animals such as dogs and mice. 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. 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 domesticate more easily 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. 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' had the effect of enhancing the bond between humans and dogs. 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.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.