Paedomorphosis

The retention by adults of traits previously seen only in the young is important in developmental biology, and consequently in evolution. It occurs in two ways. In neoteny (/niːˈɒtᵻni/ /niːˈɒtni/ or /niːˈɒtəni/, also called juvenilization), the physiological (or somatic) development of an organism (typically an animal) is slowed or delayed. Neoteny is found in modern humans.

In contrast, in progenesis (paedogenesis), sexual development occurs faster. Both processes result in paedomorphism (or paedomorphosis), a type of heterochrony. Some authors define paedomorphism as the retention of larval traits, as seen in salamanders.

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 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.

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