Neoteny

Neoteny is a type of heterochrony, specifically a developmental process in which juvenile characteristics are retained in the adult form. It is a form of paedomorphosis, where the adult of a species retains traits previously seen only in juveniles. In essence, neoteny results in a slowing down or retardation of the physiological development of an organism. This developmental delay affects somatic (bodily) features more than reproductive development, allowing the organism to reach sexual maturity while still possessing juvenile physical characteristics.

Neoteny can be driven by a variety of evolutionary pressures, including environmental factors that favor juvenile traits in the adult stage. It can lead to significant morphological and physiological differences between closely related species. The degree of neoteny can vary, with some species exhibiting only a few juvenile traits while others retain a more significant suite of them.

The term "neoteny" was coined by Julius Kollmann in 1885 to describe the retention of larval features in the axolotl salamander. However, the concept has since been applied to a broader range of organisms and evolutionary scenarios.

Neoteny is often contrasted with progenesis, another form of paedomorphosis. In progenesis, development is accelerated, leading to a premature cessation of growth and a smaller adult size. While both neoteny and progenesis result in paedomorphic adults, they achieve this through different developmental mechanisms (slowing down versus speeding up development, respectively).

The study of neoteny is important for understanding evolutionary processes, particularly the evolution of novel forms and the diversification of species. It provides insights into the complex interplay between genes, development, and the environment.