Neoteny in the context of Evolutionary developmental biology

The concept of sexual selection was introduced by Charles Darwin as an element of his theory of natural selection. Sexual selection is a biological way one sex chooses a mate for the best reproductive success. Most compete with others of the same sex for the best mate to contribute their genome for future generations. This has shaped human evolution for many years, but reasons why humans choose their mates are not fully understood. Sexual selection is quite different in non-human animals than humans as they feel more of the evolutionary pressures to reproduce and can easily reject a mate. The role of sexual selection in human evolution has not been firmly established although neoteny has been cited as being caused by human sexual selection. It has been suggested that sexual selection played a part in the evolution of the anatomically modern human brain, i.e. the structures responsible for social intelligence underwent positive selection as a sexual ornamentation to be used in courtship rather than for survival itself, and that it has developed in ways outlined by Ronald Fisher in the Fisherian runaway model. Fisher also stated that the development of sexual selection was "more favourable" in humans.

The axolotl (/ˈæksəlɒtəl/ ; from Classical Nahuatl: āxōlōtl [aːˈʃoːloːtɬ] ) (Ambystoma mexicanum) is a species of paedomorphic mole salamander, meaning they mature without undergoing metamorphosis into the terrestrial adult form; the adults remain fully aquatic with obvious external gills. This trait, although somewhat unusual among the majority of amphibians, is not unique to axolotls. Furthermore, this is apparent as axolotls may be difficult to distinguish from the larval stage of other neotenic adult mole salamanders (Ambystoma spp.), such as the occasionally paedomorphic tiger salamander (A. tigrinum) which are widespread in North America; or with mudpuppies (Necturus spp.), which bear a superficial resemblance to axolotls, but are from a different family of salamanders.

Axolotls originally inhabited a system of interconnected wetlands and lakes in the Mexican highlands; they were known to inhabit the smaller lakes of Xochimilco and Chalco, and are also presumed to have inhabited the larger lakes of Texcoco and Zumpango. These waterways were mostly drained by Spanish settlers after the conquest of the Aztec Empire, leading to the destruction of much of the axolotl's natural habitat, which is now largely occupied by Mexico City. Despite this, they remained abundant enough to form part of the staple in the diet of native Mexica during the colonial era. Today, due to continued urbanization in Mexico City, which causes water pollution in the remaining waterways, as well as the introduction of invasive species such as tilapia and carp, the axolotls are now near extinction. This can be seen as the species has been listed as critically endangered in the wild, with a decreasing population of around 50 to 1,000 adult individuals, by the International Union for Conservation of Nature (IUCN), and is listed under Appendix II of the Convention on International Trade in Endangered Species (CITES).

The mole salamanders (genus Ambystoma) are a group of advanced salamanders endemic to North America. The group has become famous due to the study of the axolotl (A. mexicanum) in research on paedomorphosis, and the tiger salamander (A. tigrinum, A. mavortium) which is often sold as a pet, and is the official amphibian of four US states.

Kofiau is an island in the Raja Ampat Islands, in Southwest Papua, Indonesia. The island is primarily raised coral limestone with some volcanic hills, covered in low forest. The island is home to the endemic Kofiau paradise kingfisher and Kofiau monarch. A new form of the Green tree python has been found on Kofiau and Boo Island that retains its neotenic yellow coloration into adulthood.