Neoteny (pronounced /niːˈɒtɨniː/), also called juvenilization, is the retention, by adults in a species, of traits previously seen only in juveniles (a kind of pedomorphosis In developmental biology, pedomorphosis or juvenification is a phenotypic and/or genotypic change in which the adults of a species retain traits previously seen only in juveniles. Pedomorphosis was first proposed by Walter Garstang in 1922. The underlying mechanisms for this include heterochrony), and is a subject studied in the field of developmental biology Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy. In neoteny, the physiological Physiology is the science of the functioning of living systems. It is a subcategory of biology. In physiology, the scientific method is applied to determine how organisms, organ systems, organs, cells and biomolecules carry out the chemical or physical function that they have in a living system. The word physiology is from Ancient Greek: φύσις (or somatic The term somatic refers to cells of the body, rather than gametes (eggs or sperm). In humans, somatic cells contain two copies of each chromosome (diploid), whereas gametes only contain one copy of each chromosome (haploid). Although all somatic cells contain identical DNA, after exposure to specific enzymes, they evolve a variety of tissue-) development of an animal or organism is slowed or delayed (fallaciously, seen as a dilation of biological time). Ultimately this process results in the retention, in the adults of a species In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are often used, such as based on similarity of DNA or, of juvenile physical characteristics well into maturity. The English English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into South-East Scotland under the influence of the Anglian medieval kingdom of Northumbria. Following the economic, political, military, scientific, cultural, and colonial influence of Great Britain and the United Kingdom from the 18th century, and of word neoteny is borrowed from the German German (Deutsch, [ˈdɔʏtʃ] ) is a West Germanic language, thus related to and classified alongside English and Dutch. It is one of the world's major languages and the most widely spoken first language in the European Union. Globally, German is spoken by approximately 120 million native speakers and also by about 80 million non-native speakers Neotenie, the latter constructed from the Greek Greek , an independent branch of the Indo-European family of languages, is the language of the Greeks. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. In its ancient form, it is the language of classical ancient Greek literature and the New Testament of νέος (young) and τείνειν (tend to). The standard adjectival form is "neotenous"[2], although "neotenic" is often used.
In invertebrate An invertebrate is an animal without a backbone. The group includes 95% of all animal species — all animals except those in the chordate subphylum Vertebrata 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.
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In evolution
Neoteny plays a role in evolution Evolution is the change in the inherited traits of a population of organisms through successive generations. After a population splits into smaller groups, these groups evolve independently and may eventually diversify into new species. Ultimately, life is descended from a common ancestory through a long series of these speciation events,, 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 Mutations are changes in the DNA sequence of a cell's genome and are caused by radiation, viruses, transposons and mutagenic chemicals, as well as errors that occur during meiosis or DNA replication. They can also be induced by the organism itself, by cellular processes such as hypermutation in or interactions between genes A gene is a unit of heredity in a living organism. It is normally a stretch of DNA that codes for a type of protein or for an RNA chain that has a function in the organism. All living things depend on genes, as they specify all proteins and functional RNA chains. Genes hold the information to build and maintain an organism's cells and pass genetic 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:
- flightless birds Birds are winged, bipedal, endothermic (warm-blooded), egg-laying, vertebrate animals. There are around 10,000 living species, making them the most varied of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from the 5 cm (2 in) Bee Hummingbird to the 2.75 m (9 ft) Ostrich—physical proportions resemble those of the chicks of flighted birds;
- humans Humans are a species of animal known taxonomically as Homo sapiens , and are the only extant member of the Homo genus of bipedal primates in Hominidae, the great ape family. However, in some cases "human" is used to refer to any member of the genus Homo—with traits such as sparse body hair and enlarged heads reminiscent of 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.
- pets, such as dogs The dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The domestic dog has been one of the most widely kept working and companion animals in human history—which share many physical features with the immature wolf The grey wolf , often known simply as the wolf, is the largest wild member of the Canidae family. Though once abundant over much of Eurasia and North America, the grey wolf inhabits a reduced portion of its former range due to widespread destruction of its territory, human encroachment, and the resulting human-wolf encounters that sparked broad (these same traits were found during the development of the tame silver fox The domesticated silver fox is the result of nearly 50 years of experiments in the Soviet Union and Russia to domesticate the silver morph of the red fox. The breeding project was set up in the 1950s by the Soviet scientist Dmitri Belyaev. As a result of selective breeding, the new foxes not only have become tamer, but more dog-like as well). 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.
In humans
Neoteny in humans can be seen in different aspects. It can be compared with other great ape The Hominidae form a taxonomic family, including four extant genera: chimpanzees, gorillas, humans, and orangutans species, between the sexes and between individuals. Some examples include:
- the flatness of the human face compared with other primates A primate is a member of the biological order Primates (/praɪˈmeɪtiːz/ prī·mā′·tēz; Latin: "prime, first rank"), the group that contains prosimians (including lemurs, lorises, galagos and tarsiers ) and simians (monkeys and apes). With the exception of humans, who inhabit every continent on Earth,[a] most primates live in
- late arrival of the teeth
Compared with other species
The idea that adult humans exhibit certain neotenous (juvenile) features, not evinced in the great apes, is about a century old. Louis Bolk made a long list of such traits,[3] and Stephen Jay Gould Stephen Jay Gould was an American paleontologist, evolutionary biologist and historian of science. He was also one of the most influential and widely read writers of popular science of his generation. Gould spent most of his career teaching at Harvard University and working at the American Museum of Natural History in New York. In the latter years published a short list in Ontogeny and Phylogeny.[4] "Man, in his bodily development, is a primate foetus that has become sexually mature" (Bolk). The human capacity for long continued learning may be construed as a juvenile trait greatly extended. However, there are, of course, significant differences between juvenile chimpanzees and adult humans, most obviously in human abstract rational thought and language and, less obviously, in the human female sexual cycle.[5] Therefore, neoteny is just one aspect of the story of human evolution.
Another theory suggests that humans' neotenous characteristics were an evolutionary strategy that enabled Cro-Magnons The Cro-Magnon were the first early modern humans (early Homo sapiens sapiens) of the European Upper Paleolithic in Europe. The earliest known remains of Cro-Magnon-like humans are radiometrically dated to 35,000 before present (Homo sapiens) to gain predominance over H. neanderthalensis The Neanderthal or /neɪˈændərtɑːl/; also spelled Neandertal) is an extinct member of the Homo genus that is known from Pleistocene specimens found in Europe and parts of western and central Asia. Neanderthals are either classified as a subspecies (or race) of humans (Homo sapiens neanderthalensis) or as a separate species (Homo (and possibly H. erectus Homo erectus is an extinct species of hominid that originated in Africa—and spread as far as China and Java—from the end of the Pliocene epoch to the later Pleistocene, about 1.8 to 1.3 million years ago. There is still disagreement on the subject of the classification, ancestry, and progeny of H. erectus, with two major alternative hypotheses: and H. heidelbergensis Homo heidelbergensis is an extinct species of the genus Homo which may be the direct ancestor of both Homo neanderthalensis in Europe and Homo sapiens. The best evidence found for these hominin date between 600,000 and 400,000 years ago. H. heidelbergensis stone tool technology was very close to that of the Acheulean tools used by Homo erectus) by appealing to these species' nurturing instincts through paedomorphic In developmental biology, pedomorphosis or juvenification is a phenotypic and/or genotypic change in which the adults of a species retain traits previously seen only in juveniles. Pedomorphosis was first proposed by Walter Garstang in 1922. The underlying mechanisms for this include heterochrony cuteness Cuteness is a kind of attractiveness commonly associated with youth and appearance, as well as a scientific concept and analytical model in ethology, first introduced by Konrad Lorenz to avoid territorial aggression. Noted anthropologist Björn Kurtén explores this concept in his paleofictional Dance of the Tiger (1980).
Between sexes
While neoteny is not necessarily a physical state experienced by humans, paedomorphic characteristics in women are widely acknowledged as desirable by men Physical attractiveness is the perception of the physical traits of an individual human person as aesthetically pleasing or beautiful, and can include various implications such as sexual attractiveness and physique. What is considered physically attractive is dependent on three factors: universal perceptions common to all human cultures, cultural. For instance, vellus hair Vellus hairs are short, fine, light colored, and barely noticed hairs, which develop on most of the human body from childhood, regardless of sex. Exceptions include the lips, the backs of the ears, the palms of hands, the soles of the feet, certain external genital areas, the navel and scar tissue. The density of hair – the number of hair is a juvenile characteristic. However, while men develop longer, coarser, thicker, and darker terminal hair Terminal hairs are thick, long, and dark, as compared with vellus hair. During puberty, the increase in androgenic hormone levels causes vellus hair to be replaced with terminal hair in certain parts of the human body. These parts will have different levels of sensitivity to androgens, primarily of the testosterone family through sexual differentiation, women do not, leaving their vellus hair visible.
Desmond Morris Desmond John Morris is a British zoologist and ethologist, but is also known as a surrealist painter and popular author discussed the importance of neoteny in human biology in The Naked Ape and The Human Zoo.
Between races
In Ashley Montagu Montague Francis Ashley Montagu , was a British-American anthropologist and humanist who popularized issues such as race and gender and their relation to politics and development. He was the rapporteur, in 1950, of the UNESCO statement The Race Question. As a young man he changed his name to "Montague Francis Ashley-Montagu" and went by &'s list of "[n]eotenous structural traits in which Mongoloids... differ from Caucasoids", Montagu lists "Larger brain, larger braincase, broader skull, broader face, flat roof of the nose, inner eye fold, more protuberant eyes, lack of brow ridges, greater delicacy of bones, shallow mandibular fossa, small mastoid processes, stocky build, persistence of thymus gland into adult life, persistence of juvenile form of zygomatic muscle, persistence of juvenile form of superior lip muscle, later eruption of full dentition (except second and third molars), less hairy, fewer sweat glands, fewer hairs per square centimeter [and] long torso"[6] "Mongoloid subjects were found to have approximately 20% higher bone density at the angle of mandible than Caucasoid subjects."[7]
In other animals
One example of a neotenic trait in vertebrates Vertebrates are members of the subphylum Vertebrata, chordates with backbones or spinal columns. About 58,000 species of vertebrates have been described. Vertebrata is the largest subphylum of chordates, and contains many familiar groups of large land animals. Vertebrates comprise cyclostomes, bony fish, sharks and rays, amphibians, reptiles, is the salamander Salamander is a common name of approximately 500 species of amphibians. They are typically characterized by their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant species are grouped together as the Urodela. Most salamanders have four toes on their front species axolotl The axolotl , Ambystoma mexicanum, is the best known of the Mexican neotenic mole salamanders belonging to the Tiger Salamander complex. Larvae of this species fail to undergo metamorphosis, so the adults remain aquatic and gilled. The species originates from the lake underlying Mexico City and is also called ajolote (which is also the common name, which usually remains fully aquatic as it matures. Other salamanders, such as the widespread tiger salamander The Tiger Salamander is a species of Mole Salamander. The proper common name is the Eastern Tiger Salamander, as to differentiate from other closely related species of North America North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and in the western hemisphere. It is bordered on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the southeast by the Caribbean Sea, and on the west by the North Pacific Ocean; South America lies to the southeast, may retain the external gills A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist. The microscopic structure of a gill presents a large surface area to the external usually only present in immature individuals, as adults in some populations in marginal habitats A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant or other type of organism. It is the natural environment in which an organism lives, or the physical environment that surrounds (influences and is utilized by) a species population.[citation needed]. The amphibian Rough-skinned Newt The rough-skinned newt is a North American newt known for its strong poison 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.[8]
Progenesis
Neoteny and progenesis Progenesis is a mechanism in developmental biology that is associated with paedomorphosis. Progenesis refers to the attainment of sexual maturity by an organism still in its larval or juvenile stage and a secondary result of never experiencing later developmental stages. Organisms that are progenetic never achieve the adult form experienced by are both mechanisms that result in paedomorphosis In developmental biology, pedomorphosis or juvenification is a phenotypic and/or genotypic change in which the adults of a species retain traits previously seen only in juveniles. Peramorphosis is change in the reverse direction. Pedomorphosis was first proposed by Walter Garstang in 1922. The underlying mechanisms for this include heterochrony. Neoteny delays physiological, but not sexual, maturity. Comparatively, progenesis Progenesis is a mechanism in developmental biology that is associated with paedomorphosis. Progenesis refers to the attainment of sexual maturity by an organism still in its larval or juvenile stage and a secondary result of never experiencing later developmental stages. Organisms that are progenetic never achieve the adult form experienced by speeds up sexual, but not physiological, maturity. Progenetic organisms achieve sexual maturity in their juvenile state. This is most commonly found among certain amphibians Amphibians , such as frogs, toads, salamanders, newts, and caecilians, are ectothermic (or cold-blooded) animals that metamorphose from a juvenile water-breathing form, either to an adult air-breathing form, or to a paedomorph that retains some juvenile characteristics. Proteidae (mudpuppies and waterdogs) are good examples of paedomorphic species and insects Insects are a class within the arthropods that have a chitinous exoskeleton, a three-part body (head, thorax, and abdomen), three pairs of jointed legs, compound eyes, and two antennae. They are among the most diverse group of animals on the planet and include more than a million described species and represent more than half of all known living.
See also
- Baby face Baby face is a quality of human facial appearance. It is the retention of juvenile facial features through puberty and adulthood
- Cuteness Cuteness is a kind of attractiveness commonly associated with youth and appearance, as well as a scientific concept and analytical model in ethology, first introduced by Konrad Lorenz
- Heterochrony In biology, heterochrony is defined as a developmental change in the timing of events, leading to changes in size and shape. There are two main components, namely the onset and offset of a particular process, and (ii) the rate at which the process operates. A developmental process in one species can only be described as heterochronic in relation
- Paedogenesis
- Pedomorphosis In developmental biology, pedomorphosis or juvenification is a phenotypic and/or genotypic change in which the adults of a species retain traits previously seen only in juveniles. Pedomorphosis was first proposed by Walter Garstang in 1922. The underlying mechanisms for this include heterochrony
- Sexual selection
References
- ^ Budiansky, Stephen (1999). The Covenant of the Wild: Why animals chose domestication. Yale University Press. ISBN The International Standard Book Number is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster, now Emeritus Professor of Statistics at Trinity College, Dublin, for the booksellers and stationers W.H. Smith and others in 1966 0300079931.
- ^ http://www.thefreedictionary.com/neotenous
- ^ Bolk, L. 1926. Das Problem der Menschwerdung. Fischer, Jena.
- ^ short-list of 25 characters reprinted in Gould, Stephen Jay 1977. Ontogeny and phylogeny. Harvard. p357
- ^ Young J.Z. 1957; 2nd ed 1975. The life of mammals. Oxford.
- ^ Montagu, Ashley. Growing Young. Published by Greenwood Publishing Group, 1989 ISBN 0897891678
- ^ Ong. R.G. Evaluation of bone density in the mandibles of young Australian adults of Mongoloid and Caucasoid descent. PubMed. 1999. Accessed September 10, 2008. [1]
- ^ C. Michael Hogan (2008) Rough-skinned Newt (Taricha granulosa), Globaltwitcher, ed. N. Stromberg [2]
Further reading
- Nancy Minugh-Purvis & Kenneth J. McNamara, ed. (2002), Human Evolution through Developmental Change, Baltimore, Maryland: John Hopkins University Press, ISBN The International Standard Book Number is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster, now Emeritus Professor of Statistics at Trinity College, Dublin, for the booksellers and stationers W.H. Smith and others in 1966 0-8018-6732-0, http://books.google.com/books?id=v2_35-suaZEC&printsec=frontcover&dq=%22human+evolution%22+%22developmental+change%22&hl=en&ei=9xVFTIyhFInSuwOgtMSODQ&sa=X&oi=book_result&ct=result&resnum=1&ved=0CCgQ6AEwAA#v=onepage&q&f=false, retrieved 20 July 2010
- Trut, Lyudmila N. (1999). "Early Canid Domestication: The Farm-Fox Experiment" American Scientist. 87(2), 160-169. (A Russian study of pedomorphosis in a 40-year breeding program to domesticate silver foxes.)
External links
- DannyReviews.com—Ontogeny and Phylogeny, Stephen Jay Gould (book review), Danny Yee (October 16, 1992)
- DavidBrin.com—“Neoteny and Two-Way Sexual Selection in Human Evolution: A Paleo-Anthropological Speculation on the Origins of Secondary-Sexual Traits, Male Nurturing and the Child as a Sexual Image,” David Brin, PhD
- Neoteny.org—“Neoteny: The multidisciplinary implications of heterochronic theory”
- NIH.gov—“Ontogenetic study of the skull in modern humans and the common chimpanzees: neotenic hypothesis reconsidered with a tridimensional Procrustes analysis,” X. Penin, C. Berge, M. Baylac, American Journal of Physical Anthropology, vol 118, no 1, p 50-62 (May, 2002)
- NHM.org—“Neoteny/Juvenilization: Some dogs look and act forever young,” Natural History Museum of Los Angeles County
- Brown, Stuart (2008) Why play is vital -- no matter your age, neoteny at 14 minutes 40 seconds, TEDtalks, TED.com
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