neotenic

Neotenic is an adjective used in biology to describe an organism that retains juvenile or larval characteristics into its adult stage. The concept is tied to neoteny, a form of heterochrony in which changes in the timing or rate of development lead to adults that resemble the younger, juvenile form of the species.

In practical terms, neoteny occurs when an individual reaches sexual maturity while somatic development remains paused or slowed, producing an adult with traits typically seen only in earlier life stages. When adult morphology closely resembles a juvenile, this pattern is often referred to as paedomorphosis. Neoteny can influence morphology, physiology, and behavior, and it is discussed within the broader framework of evolutionary development.

Famous examples include the axolotl (Ambystoma mexicanum), a salamander that remains in larval form with gills and aquatic adaptations yet becomes sexually mature. Other paedomorphic salamanders show similar patterns. Neoteny is also a topic of discussion in humans and domesticated animals, where some researchers describe retained juvenile traits—such as specific craniofacial proportions or social behaviors—as neotenic relative to related taxa. While not universal, these discussions highlight neoteny as a potential factor in the evolution of morphology and life-history strategies.

Importance and scope: understanding neoteny provides insight into how developmental timing shapes evolutionary outcomes. It is studied across evolutionary biology, developmental biology, and zoology, and is contrasted with other forms of heterochrony that alter the course of development in different ways.