The word neoteny rests on a Greek-Latin mix-up by its own inventor
Julius Kollmann coined neoteny in 1885 for the axolotl, which grows up without leaving its gilled larval body. He meant retaining youth, but seems to have confused a Greek verb meaning to stretch with the Latin one meaning to hold, so the name technically says stretching youth.
Neoteny is the slowing or delaying of an organism's development so that adults keep features normally seen only in the young. Humans show more of it than other primates: large heads, flat faces and fairly short arms compared with apes. In 1926 the anatomist Louis Bolk called it the main process that made us human. Stephen Jay Gould, writing in 1977, pointed out that Bolk's version was used to prop up racist and sexist claims, yet granted him the central insight that we reach sexual maturity in a body that stays infant-like. J. B. S. Haldane similarly described a lengthening childhood as a major human trend, and some researchers suspect sexual selection for youthful faces played a part.
Domestic animals are the classic example, but with a twist. Breeding for companionship pushed dogs toward puppyish traits like short snouts, big eyes and wide-set gazes, and the Cavalier King Charles Spaniel looks like a puppy for life. Yet a 2004 study of 310 wolf skulls and more than 700 dog skulls from 100 breeds concluded that neoteny cannot generally explain how dog skulls evolved. By 2011 the same researcher put it bluntly: dogs are not paedomorphic wolves.
In the wild the logic is often about energy. Metamorphosis is costly, so at high altitudes and in cold places salamanders that stay larval can survive better and breed more. Iodine plays a role too: salamander larvae that take in enough of it quickly transform into larger land-dwelling adults, while those in iodine-poor water stay small and aquatic. The axolotl and the cave-dwelling olm keep their gills for life, and fossil evidence suggests a Middle Jurassic amphibian did the same.
Insects in cold climates often skip wings, since wings shed heat fast. Aphids grow them only when a host plant runs short. Even cells show the pattern: one fruit fly sperm centriole keeps a juvenile structure.
Source: Neoteny
