Neoteny

Neonenia ( ancient Greek νέος - young, τείνειν - stretch) - a phenomenon observed in some arthropods, worms, amphibians, as well as in many plants, in which the maturity and end of ontogenesis occurs in early stages of development, for example, in larval stage. In this case, the individual may reach the adult stage or not reach it.

Axolotl

A typical example of neoteny is represented by axolotls , neotenic larvae of the amphibian- tailed amphibians of the genus Ambystoma , which, due to the hereditary deficiency of the thyroid hormone, remain at the larval stage. Axolotls are not inferior in size to adults. Sometimes axolotl metamorphosis occurs - with a gradual change in the conditions of existence ( drying up of the reservoir ) or with hormonal injection .

Neoteny is an important process from the point of view of evolution , since it causes the loss of a hard specialization, more typical for the final stages of development than for the larval ones.

In a broad sense, neoteny (juvenilization) is also understood as the manifestation of features in adult individuals, in different conditions (previously in the same species, in related species, in other populations) characteristic of children. For example, a person ( Homo sapiens ) differs from apes in the structure of the hair coat (the body hair region in humans coincides with those in the fetus of apes), as well as late ossification (including the skull ). Incomplete ossification is a juvenile characteristic . Later, the ossification of the skull does not prevent the growth of the brain .

In addition, there is a hypothesis that the macroevolution of the group of chordates is associated with neoteny. Representatives of the uncranial subtype ( Acrania ) are similar in organization to the larvae of representatives of the submarine subtype ( Tunicata ). Perhaps the uncranial descended from ancestors similar to the tunicates, as a result of neoteny. Uncranial - more primitive group compared with the third group of chordates - vertebrates ( Vertebrata ).

The transition in plants of a number of groups from tree to herbaceous (long neoteny), that is, the loss of the final stages of development, is also called neoteny and causes an increase in evolutionary plasticity ^[1] . An example of neoteny is also considered to be the simplification of the gametophyte in the series of ferns - seed plants , as well as the reduction of the sporophyte in bryophytes while maintaining reproductive functions in both cases.