The retention of juvenile somatic and psychic traits into adulthood. Neotony is the mechanism, one form of heterochrony, that allows Axalotl salamanders to reproduce as tadpoles. This "procrastination" of maturation isn't a rare phenomena in nature.
Changes in developmental timing can and do trigger whole suites of changes in individuals and species and it is widely believed that neotony is a major factor in what makes us human. For further reading......Stephen Jay Gould's book, Ontogeny and Phylogeny