Neoteny
Neotenie or Neotänie ( Gr. Νέος neos 'young' and τείνειν teínein 'stretch', 'expand') describes in zoology the onset of sexual maturity in the larval state without metamorphosis , e.g. B. in tailed amphibians . The term was coined in 1885 by the zoologist Julius Kollmann while studying developmental delays in tadpoles.
The term was later used in domestication research for the phenomenon of youthfulness, the retention of youth traits.
Neoteny in the sense of sexually mature larval form
The best-known example is the axolotl , Ambystoma mexicanum , a newt from the cross-toothed newt family that lives in Lake Xochimilco in Mexico . This species becomes sexually mature in a late larval stage - with developed legs but still with gills. Physiologically, the neoteny is triggered by an underactive thyroid , which genetically causes insufficient amounts of maturation hormones to be produced, or by a severe deficiency of mineral iodine in the water. If you feed axolotl with such hormones, they mature into adult animals and, like the closely related tiger salamanders , go ashore.
Neoteny occurs in many tail amphibians of different families, but there are different forms of this phenomenon. In iodine-poor mountain waters, permanent larvae of newts and salamanders occasionally occur, but these can be metamorphosed with the help of thyroid hormones . This phenomenon occurs not only with domestic newts such as the mountain newt, but also with the American transverse-tooth newts, to which the axolotl belongs. On the other hand, some other species, regardless of the iodine content of the water, have switched to a permanent larvae lifestyle that cannot be induced to transform into land animals even by hormone administration. A typical example of this phenomenon is the European olm .
Neoteny is also found in some species of insects, such as moths , beetles, and fan-winged birds .
Accelerated development of reproductive functions is also known as pedogenesis .
Neoteny as youthfulness
Neoteny in animals
In mammals , too , one speaks of neoteny when these are youthful characteristics in connection with domestication , such as B. keep a shortened snout, a special coat pattern or floppy ears. Through the neotenic characteristics and the child-like schema embodied by them, a caring and caring behavior is activated in humans, which leads to a selection advantage for the corresponding animal. Pets in particular often show such characteristics.
Neotenic features in mammals (especially caused by domestication ) have been clearly described by Hermann von Nathusius , Louis Bolk and various modern research groups. For example, a Russian research group that has selected foxes for tameness over 40 generations describes a large number of neotenic traits that occurred in this selected fox population.
Nevertheless, neoteny is not, as has often been assumed since the 1920s, a general phenomenon of domestication.
Neoteny in botany
Neoteny states that youth structures can be preserved in the long term. For example, herbs can be viewed as the fixed youth stages of woody plants. An example is paeonia (peony), in which the original forms are lignified and show secondary growth in thickness. In phylogeny , less and less secondary wood was formed and the parenchymal pith and medullary rays broadened. Ultimately, only the primary xylem remained and herbaceous forms emerged.
In a few carnivorous plants , trap mechanisms develop only in their youth stage, but in most of them the carnivory remains throughout life. The carnivory brings the plants immense advantages over non-carnivorous plants. While plants that are not carnivorous are in constant competition for nutrients in nutrient-poor areas, carnivorous plants have a much broader spectrum of foods, so the trapping mechanisms in some carnivorous plants develop extremely early, sometimes even before the cotyledons. These observations suggest that the origin of carnivory has to do with seedling establishment and that the formation of traps in adult plants is a case of neoteny.
Neoteny in humans
From 1921 Emile Devaux applied this term to the origin of man. Around the same time, the Dutch anatomist Lodewijk (Louis) Bolk developed his theory of fetalization. According to this, the human being is a monkey that is severely delayed in its development - or a monkey fetus that has prematurely reached sexual maturity. It was also claimed that the “ Mongolids ” were more “pedomorphic” (“racial neoteny”).
Bolk cited the following features on the skull as arguments for this:
- the size and roundness of the head
- the small part of the face compared to the whole head
- the late ossification of the skull sutures
- the position of the foramen magnum
and other anatomical features in humans:
- the upright gait as stopped embryonic development
- the strong, non-splayed and non-opposable big toes
- the ventrally directed vaginal canal
- the sparse body hair
- the lack of pigmentation
Bolk also assessed man's long lifespan as an indication of this theory.
The neoteny hypothesis of hominization is not in contrast to other explanatory models for, for example, walking upright. While the savannah hypothesis, among other things , tried to provide an explanatory model under which selection conditions this special human trait developed, the neoteny hypothesis explains how these traits could have come about physiologically. The mechanism of neoteny represents a form of pre-adaptation .
Individual evidence
- ↑ a b Erik Zimen: The dog - descent, behavior, man and dog . Goldmann, 1992, ISBN 3-442-12397-6 .
- ^ Benjamin A. Pierce & Hobart M. Smith (1979): Neoteny or Paedogenesis? In: Journal of Herpetology. Volume 13, Number 1, pp. 119-121.
- ↑ LN Trut et al .: An Experiment on Fox Domestication and Debatable Issues of Evolution of the Dog. Russian Journal of Genetics, June 2004, pp. 644-655 ( doi: 10.1023 / B: RUGE.0000033312.92773.c1 )
- ↑ L. Bolk: The problem of becoming human , Jena 1926 (source after Zimen Der Hund ).
- ↑ Prof. Rainer Knußmann, Handbook of Comparative Biology and Human Genetics of Humans, 1996.