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Neoteny (), also called juvenilization,Montagu, A. (1989). Growing Young. Bergin & Garvey: CT. is the delaying or slowing of the Physiology, or somatic, development of an organism, typically an animal. Neoteny in modern humans is more significant than in other primates. In progenesis or paedogenesis, sexual development is accelerated.Volkenstein, M. V. 1994. Physical Approaches to Biological Evolution. Springer-Verlag: Berlin, [1].
Both neoteny and progenesis result in paedomorphism (as having the form typical of children) or paedomorphosis (changing towards forms typical of children), a type of heterochrony. 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.Schell, S. C. Handbook of Trematodes of North America North of Mexico, 1985, pg. 22Ginetsinskaya, T.A. Trematodes, Their Life Cycles, Biology and Evolution. Leningrad, USSR: Nauka 1968. Translated in 1988, [2].
The word neoteny is borrowed from the German language Neotenie, the latter constructed by Kollmann from the Greek language νέος ( neos, "young") and τείνειν ( teínein, "to stretch, to extend"). The adjective is either "neotenic" or "neotenous". Neoteny, The Free Dictionary. 2011. Accessed April 30, 2011. For the opposite of "neotenic", different authorities use either "gerontomorphic"Henke, W. (2007). Handbook of paleoanthropology, Volume 1. Springer Books, NY.Hetherington, R. (2010). The Climate Connection: Climate Change and Modern Human Evolution. Cambridge University Press. or "peramorphosis".Hall, B.K., Hallgrímsson, B. Monroe, W.S. (2008). Strickberger's evolution: the integration of genes, organisms and populations. Jones and Bartlett Publishers: Canada. 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.
When the role of dogs expanded from just being working dogs to also being companion dog, humans started selective breeding dogs for morphological neoteny, and this selective breeding for "neoteny or paedomorphism" "strengthened the human-canine bond." 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.Beck, A.M. & Katcher, A.H. (1996). Between Pets and People: The Importance of Companionship. West Lafayette, Indiana: Purdue University Press. 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.McGreevy, P.D. & Nicholas, F.W. (1999). Some Practical Solutions to Welfare Problems in Dog Breeding. In Animal Welfare. 8: 329–341.
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.Drake, Abby Grace, "Evolution and development of the skull morphology of canids: An investigation of morphological integration and heterochrony" (January 1, 2004). Doctoral Dissertations Available from Proquest. Paper AAI3136721. link By 2011, the findings by the same researcher were simply "Dogs are not paedomorphic wolves."
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. Under these environmental conditions, dispersal would be disadvantageous; heat is lost more rapidly through wings in colder climates. The Larviform female 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. 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.
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. 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. 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.
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.
share many physical characteristics with humans, including neotenous skulls. 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.
In some groups, such as the insect families Gerridae, Delphacidae and Ground beetle, energy costs result in neoteny; many species in these families have brachyptery, neotenous wings or aptery. Some cricket species shed their wings in adulthood; in the genus Ozopemon, males (thought to be the first example of neoteny in ) are significantly smaller than females due to inbreeding. In the termite Kalotermes flavicollis, neoteny is seen in molting females.
In other species, such as the northwestern salamander ( Ambystoma gracile), environmental conditionshigh altitude, in this casecause neoteny. Neoteny is also found in a few species of the crustacean family Ischnomesidae, which live in deep ocean water.
Neoteny is an ancient, pervasive phenomenon. In urodeles, many extant taxa are neotenic, and both morphological and histological data suggest that the Middle Jurassic taxon Marmorerpeton was neotenic.
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