Neoteny describes a process by which paedomorphism is achieved, and is a subject studied in the field of developmental biology. In neoteny, the physiological (or somatic) development of an animal or organism is slowed or delayed. Ultimately this process results in the retention, in the adults of a species, of juvenile physical characteristics well into maturity. The English word neoteny is borrowed from the German Neotenie, the latter constructed from the Greek νέος (young) and τείνειν (to extend).
Specific individual traits that differ in descendant organisms, when compared to ancestors, are sometimes called neotenies; humans, for example, appear to have several neotenies in comparison to chimpanzees.
Neoteny in humans
There is controversy over whether adult humans exhibit certain neotenous features, or juvenile characteristics, that are not evidenced in other great ape species. Stephen Jay Gould was an advocate of the view that humans are a neotenous species of chimpanzee; the argument being that juvenile chimpanzees have an almost-identical bone structure to humans, and that the chimpanzee�s ability to learn seems to be cut off upon reaching maturity.
While neoteny is not necessarily a physical state experienced by humans, paedomorphic characteristics in women are widely acknowledged as desirable by men (see Sexual attraction). Desmond Morris discusses the importance of neoteny in human sociobiology in The Naked Ape, The Human Animal, and the The Human Zoo.
It is also worthy to note that paedomorphic variations not only exist between the sexes, but also between individuals, with some people displaying more characteristics of neoteny than others. This trend carries over to variations among ethnic groups as well.
One example of a neotenic trait in vertebrates is the salamander species axolotl, which usually remains fully aquatic as it matures.
It is also theorized that the phylum Chordata first originated as a result of paedomorphism occurring in a highly primitive animal such as a sponge or coral.
Neoteny and progenesis
Neoteny and progenesis are both mechanisms that result in paedomorphosis. Neoteny delays physiological and sexual maturity. Comparatively, progenesis halts development of the organism before achieving the adult maturity experienced by its ancestors. Progenetic organisms achieve sexual maturity in this juvenile state and is found among certain amphibians and insects.
Neoteny also plays a role in evolution, as a means by which, over generations, a species can undergo a significant physical change. In such cases, a species� neotenous form becomes its �normal� mature form, no longer dependent upon environmental triggers to inhibit maturity. The mechanism for this could be a mutation in, or interactions between, genes involved in maturation, inhibiting their function.
To be neotenous needs a realisation of its condition. It affects all the primates. Most of the chimps studied, for example, lose their neoteny at about 2-3 years. Most adult humans lose their neoteny between the 14th and 17th year. But in some, neoteny remains; and that is a quest to learn and get better and find out things.
Neoteny is not the only contributing factor affecting maturation in species that may have undergone neotenous changes over the course of their evolution, and its actual involvement in the following examples is not well understood:
- flightless birds- physical proportions resemble those of the chicks of flighted birds;
- humans- with traits such as sparse body hair and enlarged heads reminiscent of baby primates.
- dogs- which share many physical features with the immature wolf
Neoteny has been written about by Kollman (inventor of the term), Bolk, Portmann, and Gould. Louis Bolk best stated the case in 1926 with this famous line: "man is a primate fetus that has become sexually mature". The human fetal growth rate period actually lasts about 22 months - at birth we are simply an extrauterine fetus at the 9 month stage with our brain still growing at the rapid fetal rate, thus did nature solve the birth canal bottleneck problem for producing big brained humans. A series of increasingly neotenic mutations probably account for mechanism of the amazing 4 fold increase in hominid brain size over the past 3 million years, and our outward appearance owes much to this phenomenon (i.e. all adult humans look like a huge primate fetus that can walk). It was once acceptable to point out in textbooks that neoteny related traits in the races of man seem to differ, with Negroids (Africans) being the least neotenic, Mongoloids (Asians) being the most neotenic, and Caucasoids (Europeans) being not quite as neotenic as Asians for several traits, including the important brain to body size ratio and in having less body hair, but more neotenic in regard to pigmentation of hair, skin, and eyes. The empirical support for this distinction is quite compelling, but it has become a somewhat sensitive subject.