In behavioral biology, imprinting is an irreversible form of learning: During a mostly relatively short, genetically determined period of time ( sensitive phase ), the reaction to a certain stimulus from the environment is so permanently included in the behavioral repertoire that this reaction appears innate after it has been imprinted . In the context of instinct theory , the phenomenon of imprinting is interpreted as the appropriation of the reaction to a key stimulus .
The English word for imprinting is used today in genetics for a special form of expression of genes (→ genomic imprinting ), which can depend on which parent the allele comes from, i.e. in a completely different context than in Field of behavioral biology.
Learning by imprinting takes place without any consideration of reward or punishment . Learning through imprinting is therefore fundamentally different from a form of learning such as learning through experience or problem solving through trial and error .
- Imprinting is characterized by the fact that it can only take place in a certain period of time, which is therefore referred to as a sensitive phase of life . Embossing cannot be made up for. The age at which this phase can be demonstrated and how long it lasts can vary greatly depending on the species.
- Imprinting is irrevocable, what is learned through it is learned particularly quickly and effectively and retained for life ; at least the triggers acquired through imprinting (“ key stimuli ”) are preferred over the long term.
- By imprinting, only narrowly limited characteristics are learned, for example a certain reaction to a certain object in the environment or a certain behavior that can be clearly distinguished from other behaviors.
- Imprinting can take place in a period of time in which the imprinted behavior cannot yet be implemented.
Variants of imprint learning
There are basically two forms of embossing: With object embossing , the animal is embossed on a certain object, for example on a conspecific. With the motoric imprinting , the animal acquires certain sequences of movements ("actions"), for example the song of some bird species. In addition to the two “classic” imprinting processes, the follow-up imprinting and the sexual imprinting, which were already described in Konrad Lorenz's early work , comparable learning processes have been demonstrated, especially in the ecological area.
The follow-up imprinting ( filial imprinting ), especially in geese (Anserini), has been researched intensively . Geese of the most diverse species are so well suited as model animals "because the behaviors directed at the parent animal and the social companion can easily and permanently be fixed on the human carer, but a sexual imprint on humans is almost impossible with these birds." The geese chicks have to learn who their mother is after they hatch, so they do not have an innate “appearance” of the mother. In the first few hours after hatching, they prefer to approach all objects in their environment that move and regularly utter vocalizations. After a few minutes in the vicinity of such an object, the chicks follow it almost unconditionally. In the natural environment, this is the animal that has hatched the eggs and keeps all strange individuals away from the nest - i.e. the mother. In the experiment with chicks, which hatched in an incubator isolated from all noise, the young test animals could also be imprinted on a soccer ball or on a wooden box in a matter of minutes. Eckhard Hess found out from mallards that the sensitive period for the imprinting of this behavior around the 15th hour after hatching shows a maximum of imprintability.
Katharina Heinroth described the imprinting as a “lightning-fast learning process” in which the observer - according to Oskar Heinroth - develops the idea that the chicks hatching in an incubator “really look at you with the intention of memorizing the image exactly”. This observation, which Oskar Heinroth published for the first time in 1911, was described in detail in the 1930s as the phenomenon of imprinting , especially by Konrad Lorenz , precisely defined and analyzed in numerous experiments. He has therefore become known, among other things, as the “father of the gray geese”: Lorenz repeatedly made sure that only he himself stayed in the immediate vicinity after chicks hatched. As a result, the chicks were imprinted on Lorenz and followed him wherever he went. Equally impressive and entertaining literary descriptions of the behavior of his gray goose Martina as well as film recordings made this variant of the coinage one of the best known facts of classical comparative behavioral research .
In behavioral research, sexual imprinting is a form of acquiring knowledge about adequate sexual partners. A special feature of sexual imprinting is that, in addition to the two main characteristics (sensitive phase and irreversibility), it is also noticeable in that there is a very large gap between the time of imprinting on the object and the execution of the associated behavior: the sensitive phase is consistent completed before the animal becomes sexually mature.
Zebra finches, for example, are already sexually imprinted towards the end of the first month of life, but only become sexually mature weeks later. For example, if zebra finches are reared by Japanese gulls ( Lonchura striata ), they later show a clear preference for animals of the species they “adopted” during courtship. Ducks imprinted on domestic chickens are also known from scientific educational films.
Katharina Heinroth, the director of the Berlin zoo , which was largely destroyed by acts of war in 1945 , acquired a young male polar bear from the Nuremberg Zoo in the spring of 1951 , who was born in December 1950 and separated from his mother as soon as he was able to eat independently. He was given a brown bear of the same age to play with in Nuremberg - and therefore also in Berlin. After a while, the Berlin Zoo was also able to acquire a young female polar bear with whom the male polar bear lived together in an agreeable manner. When both polar bears were sexually mature, however, the male polar bear did not care for the female. But when a brown bear in the adjacent enclosure came into the rut and her smell wafted into the polar bear enclosure through a slide let into the opaque partition wall, the polar bear scratched and scraped the slide with all his might. Once Heinroth had the slide opened, whereupon the polar bear immediately switched to the neighboring cage: “She received him upright on his hind legs, hissing, with an open mouth and punching him with his front paws. He quickly got back into his cage. It is strange that the smell of the male brown bear alone could have shaped him sexually. The sensitive phase is therefore already in the first months after the first independent feeding. ”In the wild, the young polar bears often stay with their mother for longer than a year, so that incorrect imprinting is avoided.
In 2000, Bochum researchers reported a study on Javabronze males , in the course of which the adult animals received a red crown feather as an artificial ornament. The offspring they raised later clearly preferred conspecifics with red ornamental feathers. The male offspring of unadorned parents, on the other hand, rejected adorned females and courted unadorned females significantly more often.
The selection of a certain habitat for some animal species is also based on experiences in their earliest youth. As a local coinage (also: home imprint , habitat embossing , environment embossing or geographical imprint ), the irreversible learning certain characteristics referred to a specific place.
It has been proven through implementation experiments, for example, in salmon , which evidently learn the specific taste of the water through imprinting in which they spent their first weeks of life.
Many sea turtles, such as the Atlantic green sea turtles , have a magnetic sense and use the earth's magnetic field to orient themselves in order to return to laying eggs on the same beach for the first time years after hatching. It is assumed that the angle of inclination of the field lines of the magnetic field at the place of birth is permanently learned through imprinting.
Under food embossing some researchers understand a durable, seemingly certain to irreversible preference for food after one may enjoy: "So in different animal groups can cause a later Nahrungsbevorzugung rearing food that remains even after the meantime the other diet."
Imprint on humans
"Various writings have been made about imprinting in humans, and there are indeed many indications for their occurrence, but no strict evidence." Irenäus Eibl-Eibesfeldt , from whom this quote comes, also pointed out that in young people it is " There are sensitive periods in development ", in which, for example, basic trust , an emotional bond with parents and gender roles develop:" Since the term imprinting is originally used for irreversible learning processes, it is advisable to first speak of imprinting learning processes in humans. "
Bernhard Hassenstein took up this suggestion in his book Behavioral Biology of the Child and discussed whether the term embossing could be applied to the “special openness of the infant to the formation of bonds” (to his parental supervisor): “Some say yes because the characteristics match . ”Hassenstein, however, objected - like Eibl-Eibesfeldt - to this view that if the sensitive phase were to be minted, no re-minting or new minting would be possible. “With children, however, in special life situations and with special personality structures, a new bond can develop even at a later age.” Hassenstein therefore advocated using the term “learning similar to imprinting” in humans. With reference to the attachment theory developed by John Bowlby , which was largely developed through the ethological concept of imprinting, the Canadian psychologist Tobias Krettenauer also argued that attachment patterns are plastic and can be changed in the course of development: “Conversely, it can be concluded from this that attachment occurs in all phases of life is equally malleable, would of course also be questionable. "At the same time, Krettenauer provided a justification for this special position of humans in relation to the phenomenon of imprinting :" If the process of imprinting in human development is less prominent than in some animal species, then this indicates that the interaction between the system and the environment is much more complex in humans. "
When Konrad Lorenz was awarded the "Nobel Prize for Physiology or Medicine" in 1973, the official justification particularly emphasized his services to research into coinage. In fact, in the 1950s in Seewiesen , immediately after founding the Max Planck Institute for Behavioral Physiology , Lorenz initially supplemented his observations from the 1930s with additional experiments and, among other things, the differences between geese and ducks and the relationship between succession and sexuality Research into coinage. These studies, in turn, gave Klaus Immelmann the impetus to research how songbirds were shaped to sing. Occasionally Lorenz is therefore the "discovery" of the phenomenon coinage attributed, though Lorenz already in 1935 in his early work , the sidekick in the environment of the bird explicitly on previous work by Oskar Heinroth was referring, in a study published in 1911 review article on the behavior of ducks , the Had clearly described the phenomenon of “imprinting”; Lorenz later permanently introduced the term coining into biological terminology.
Oskar Heinroth is not the discoverer of the coinage either, although Heinroth's wife Katherina and many others in the German-speaking area have ascribed this achievement to him: Oskar Heinroth had a scientific predecessor in the British Douglas Alexander Spalding (approx. 1840–1877), who used this special learning method In February 1873, although scientifically correct as stamping in ("stamping", "imprinting") described, but rather hidden in Macmillan's magazine and without carrying out in-depth experiments. Nonetheless, this publication was quoted extensively and very benevolently by William James in his “Principles of Psychology” in 1890 , and Spalding is therefore sometimes considered the “real” discoverer of the coinage in the English-speaking world. However, Spalding's studies only became known to wider circles after 1954, when John Burdon Sanderson Haldane reissued them.
This, in turn, is hardly comprehensible even from a British point of view, because the historical trace of the supposed scientific first descriptions reaches back at least as far as Utopia , i.e. the early 16th century. In Thomas More states as follows literally on the agriculturally active Utopians: "Poultry dragging on in infinite quantities, with the help of an amazing device: The hens do not breed namely the egg itself, but it requires a large number of eggs a uniform Warmth out, thus awakens life and raises the chicks. As soon as these have slipped out of the shell, they run after the people like behind the mother hen and see them as this . "
Seen in this way, the discovery of the coinage cannot be absolutely determined, because the knowledge that ducks in particular are occasionally unreliable breeders and that it is best to slip their clutch of a hen in order not to lose it, is almost as old as animal breeding.
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