Paedomorphosis has occurred when reproduction is seen in what was ancestrally a juvenile morphological stage. This can be the result of neoteny or progenesis.

Pedomorphosis may have two important evolutionary effects:

• It may stop recapitulation that occurs during the development of the organism.

• It may be important in the origin of higher taxa (see taxonomy). The first component of the argument is empirical. For many large groups of animals, the adults appear to resemble an early developmental stage of a possible ancestor.

The Mexican axolotl opposite is a famous example of paedomorphosis, retaining in maturity the feathery gills that related species lose in infancy.

Is the Mexican axolotl neotenous or progenetic?