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In developmental biology, pedomorphosis or juvenification is a phenotypic and/or genotypic change in which the adults of a species retain traits previously seen only in juveniles. Peramorphosis is change in the reverse direction. Pedomorphosis is common in many animal species domesticated by humans, including dogs, chickens, pigs and cattle. It is believed to be a side-effect of the selective pressure of human-directed breeding for juvenile behavioral characteristics such as docility. Natural pedomorphosis occurs in many species of Amphibians, especially Ambystomatid and Protean salamanders. Pedomorphosis in amphibians can be obligate or facultative. An example of this would be some salamanders which retain the gills which, in most amphibians, are lost upon reaching adulthood. It's assumed that at some point in the past, their gills were lost just like all others, but some genetic change caused them to be retained, at a point where it was evolutionarily advantageous or neutral. There are several kinds of pedomorphism which may appear independently or in combination: Humans are thought to be pedomorphic, due to their flattened face, short jaw, and bulbous forehead compared to other adult primates.
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