Neoteny
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.
[11][12][13] 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.
[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] 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.
B. S. Haldane states a "major evolutionary trend in human beings" is "greater prolongation of childhood and retardation of maturity.
"[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.
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.
[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.
Ambystoma tigrinum retains its neoteny for a similar reason; however, the retention is permanent due to the lack of available resources throughout its lifetime.
[36] Under these environmental conditions, dispersal would be disadvantageous; heat is lost more rapidly through wings in colder climates.
[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.
Axolotl and olm are perennibranchiate salamander species which retain their juvenile aquatic form throughout adulthood, examples of full neoteny.
[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.
[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.
