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Neoteny (IPA: /niːˈɒtɨniː/), also called juvenilization, is the retention, by
adults in a species, of traits previously seen only in juveniles (pedomorphosis
/paedomorphosis), 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 (alternatively, seen as a dilation of biological
time). 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 (tend to). The standard adjectival form is
"neotenous",[citation needed] although "neotenic" is often used.
In vertebrate biology, neoteny is most easily identified when sexually mature,
completely viable juveniles or larvae are found.
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.
Contents
[hide]
o 2.1 Compared to other species
o 2.2 Between sexes
o 2.3 Between individuals
[edit] In evolution
Neoteny 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, changing
their function to impede this process.
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:
flighted birds;
baby primates. Lactose tolerance in adults is a form of neoteny now considered
normal in certain populations that traditionally consume cow's milk while most
other humans are lactose intolerant as adults. It corresponds to a mutation
that permits the digestion of lactose beyond the lactation period.
(these same traits were found during the development of the tame silver fox).
Such puppy-like traits may have made early dogs seem "cute" and less
threatening than wolves, leading to both natural and artificial selection of
such dogs.
It is possible that the origin of the chordates (the phylum including all
vertebrates) was the result of an instance of neoteny. Molecular evidence
suggests that the nearest relatives of the chordates are the tunicates, marine
filter feeders. Although sessile in their adult, sexually mature form,
tunicates have a motile larval dispersal form, which has a notochord similar to
that found in chordates. At some point, the motile larvae of the tunicate
became sexually mature before metamorphosis. As a sexually active pelagic
organism it had considerable feeding and habitat colonization advantages over
the sessile form, so was at an evolutionary advantage. However, the alternative
- that the sessile form developed later and the pelagic form was ancestral - is
also thought possible (based on the fact that many jellyfish undergo the
reverse: a sessile polyp phase, followed by the familiar soft, highly mobile
adult form).
[edit] In humans
see:The Naked Ape
Neoteny in humans can be seen in different aspects. It can be compared with
other great ape species, between the sexes and between individuals. Some
examples include:
doesn't fully complete growth until about 23, also at birth a human has only
32% of the brain size it will eventually have.[citation needed]
[edit] Compared to other species
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 is 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.
Another theory suggests that humans' neotenous characteristics were an
evolutionary strategy that enabled Cro-Magnons (Homo sapiens) to gain
predominance over H. neanderthalensis (and possibly H. erectus and H.
heidelbergensis) by appealing to these species' nurturing instincts through
paedomorphic cuteness to avoid territorial aggression. Noted anthropologist Bj
rn Kurt n explores this concept in his paleofictional Dance of the Tiger
(1980).
[edit] Between sexes
While neoteny is not necessarily a physical state experienced by humans,
paedomorphic characteristics in women are widely acknowledged as desirable by
men. For instance, vellus hair is a juvenile characteristic. However, while men
develop longer, coarser, thicker, and darker terminal hair through sexual
differentiation, women do not, leaving their vellus hair visible.
Desmond Morris discusses the importance of neoteny in human biology in The
Naked Ape and The Human Zoo.
[edit] Between individuals
Paedomorphic variations also 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.
Bruce Charlton, Reader in evolutionary psychiatry at Newcastle University, UK,
suggests that there may be such a thing as "psychological neoteny." [2] Due to
recent changes in culture, he says, In a psychological sense, some
contemporary individuals never actually become adults. Delayed maturity might
be a consequence of later parenthood, itself caused by more prolonged formal
education. [3]
Similarly, Juliet Schor suggests in Born to Buy that people raised in a modern
consumer culture never attain an adult level of self-sufficiency. These
"infantilized adults" remain dependent on mass-produced products in the same
way that a child is dependent upon parents.
[edit] In other animals
One example of a neotenic trait in vertebrates is the salamander species
axolotl, which usually remains fully aquatic as it matures. Other salamanders,
such as the widespread tiger salamander of North America, may retain the
external gills usually only present in immature individuals, as adults in some
populations in marginal habitats. The amphibian Rough-skinned Newt exhibits
neoteny in numerous populations, with noted preference in certain geographic
areas; moreover, the phenomenon of gill retention in this newt manifests
gradations of neoteny in some populations, such that partial gill retention is
seen in some individuals.[4]
[edit] Neoteny and progenesis
Neoteny and progenesis are both mechanisms that result in paedomorphosis.
Neoteny delays physiological, but not sexual, maturity. Comparatively,
progenesis speeds up sexual, but not physiological, maturity. Progenetic
organisms achieve sexual maturity in their juvenile state. This is most
commonly found among certain amphibians and insects.