In heterochrony, the retention of ancestral juvenile characters by descendant adults. Paedomorphosis is if the rate of shape change is reduced or the period of operation is contracted such that a descendant adult passes through fewer growth changes and as such resembles a juvenile stage of its ancestor. This can occur by progenesis, neoteny, or post-displacement. This was coined by W. Garstang in the 1920s as part of the reaction to the Biogenetic Law when he recognized that ontogeny did not always recapitulate phylogeny but sometimes created it. The Biogenetic Law has been somewhat superseded by the concept of peramorphosis. Both processes are now recognized to play important roles in evolution. See Gould (1977) and McKinney and McNamara (1991).

the retention of juvenile characteristics by adult organisms.

retention of some junvenile features into the adult. Slowing down of development of juvenile features.See also neoteny