Neoteny

Neoteny is a form of heterochrony, a developmental change in the timing or rate of growth. In neoteny, somatic development proceeds more slowly than in the ancestral lineage, so the sexually mature individual retains juvenile or larval characteristics that would normally be lost at adulthood. In the broader sense, paedomorphosis refers to the retention of juvenile traits in adults; neoteny is the mechanism by which this retention occurs, whereas other forms of paedomorphosis (such as progenesis) involve changes in the onset of sexual maturity.

Examples of neoteny occur across diverse groups. The axolotl (Ambystoma mexicanum) is a classic case: individuals reach sexual maturity while retaining larval features such as external gills and an aquatic lifestyle. In domesticated dogs, several researchers have described neotenous traits relative to wolves, including skull morphology and sociable behavior, suggesting that selection during domestication favored juvenile characteristics in adults. The idea that domestication may promote neoteny remains a debated hypothesis but has influenced discussions of dog-wolf evolution.

In humans, some researchers have argued that neoteny contributes to certain craniofacial and behavioral traits when compared with other primates, though this interpretation is contested and part of broader debates about human evolution and development.

Neoteny is a central concept in evolutionary developmental biology (evo-devo). It helps explain how shifts in developmental timing can generate morphological and functional diversity without requiring new genes, and it is studied in zoology, paleontology, and comparative anatomy to understand growth, reproduction, and adaptation.