paedomorphic

Paedomorphosis, or paedomorphism, is an evolutionary process in which the mature stage of an organism retains traits that are juvenile in the ancestral species. The term combines Greek words for “child” (paedo) and “form” (morphe). It is a form of heterochrony, an alteration in the timing or rate of developmental events. In paedomorphosis, the adult resembles the juvenile of its ancestor.

The two most common routes are neoteny, in which the tempo of development is slowed so juvenile characteristics persist into adulthood, and progenesis, in which sexual maturation occurs earlier than somatic development, yielding an adult with juvenile features. Other forms of heterochrony can alter or exaggerate traits, contributing to variations observed among related species.

Examples and significance: The axolotl (Ambystoma mexicanum) is the classic example of paedomorphosis in vertebrates, remaining aquatic and gilled as an adult. In mammals, paedomorphic trends are discussed in relation to domesticated dogs versus wolves and, to some extent, in humans compared with other primates, noting traits such as facial proportions and skull features, though interpretations vary and are debated. Paedomorphosis is a key concept in evolutionary biology, helping explain how developmental timing shapes morphology, diversity, and the appearance of species over time.

Relation to other concepts: It is distinct from peramorphosis, where adult traits are exaggerated beyond the ancestral adult form, and from broader heterochronic changes that do not involve retention of juvenile traits.