Neoteny

Neoteny is a form of heterochrony in which an organism reaches sexual maturity while retaining traits characteristic of its juvenile stage. It can alter body form and development without delaying reproductive maturity.

Heterochrony: Evolutionary change in the timing or rate of developmental processes. Neoteny is one way altered developmental timing changes adult form.
Axolotl: A Mexican salamander that commonly reproduces while retaining larval features, including external gills. Its reproductive adults retain conspicuous aquatic larval anatomy.
Julius Kollmann: A nineteenth-century German anatomist who introduced the term neoteny. Kollmann named the phenomenon while discussing amphibian development.
Amphibian metamorphosis: The developmental transformation by which many amphibians change from aquatic larvae into adults. Neoteny can bypass or greatly reduce this transformation while allowing reproduction.
Progenesis: A form of paedomorphosis caused by accelerated reproductive development relative to body development. Like neoteny, it can yield adult juvenile features, but through earlier reproductive maturity.
Paedomorphosis: The evolutionary retention of ancestral juvenile features in adults of a descendant lineage. Neoteny is one developmental route by which paedomorphosis can arise.
Ambystoma mexicanum: The scientific name of the axolotl, a neotenic salamander native to Mexico. This species is the classic example of neoteny in amphibians.
Ernst Haeckel: A German biologist known for evolutionary theories of development and the biogenetic law. His recapitulation ideas shaped early debates about juvenile traits in adults.
Island gigantism: The evolutionary tendency for small-bodied animals to become larger on islands. Developmental timing changes, including neoteny, have been proposed in explanations of some size shifts.
Postdisplacement: A heterochronic change in which the onset of a developmental process occurs later. It differs from neoteny’s slowed development of juvenile traits relative to reproductive maturity.

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