Paedomorphosis

Paedomorphosis is a term used to describe an evolutionary transformation via 'heterochrony' which is characterized by the retention of ancestral juvenile characters in later ontogenetic stages of descendants. Several distinct processes may underlie paedomorphic juvenilization: 'neoteny' involves a retardation of somatic development relative to the timing of sexual maturity and terminal size in descendants; 'progenesis' implies precocious sexual maturation such that previous adult features or shapes are never attained in descendants; and 'hypomorphosis' results when simple size decreases yields a juvenilized phenotype in descendants through truncation of ancestral allometric (size/shape) trajectories. Case studies of paedomorphosis ranging from snails to salamanders and porpoises to humans are considered here in terms of phenotypic transformations, genetic controls, and ecological contexts.