Imprinting is used in psychology and ethology to describe any kind of learning that occurs at a particular age or stage of development. A phase-sensitive type of learning, it involves an organism recognizing the characteristics of certain stimuli that are subsequently "imprinted" onto the subject. Most occurrences involve learning to recognize one's parents or potential sexual partners, both of which have value for the survival of the species. Although most commonly observed in birds, this process has been observed in other species, leading to advances not only in the ability to assist various species but also in understanding how similar processes are involved in human development.
Imprinting was initially researched in detail by Konrad Lorenz, through his naturalistic studies of geese. The image of Lorenz followed by a family of goslings became familiar to many. Applications of this knowledge have been put to good use, ensuring that young raised in captivity learn survival skills, and, thus, can function in a relatively natural type of situation or even be re-introduced into the wild.
Outline of the theory
The most commonly found form of imprinting is known as "filial imprinting." Filial imprinting occurs when a young animal recognizes the characteristics of its parent. It is most obvious in nidifugous birds (who leave the nest shortly after hatching) and reptiles, who imprint on their parents.
Filial imprinting was first reported in domestic chickens, by the nineteenth century amateur biologist Douglas Spalding. It was rediscovered by the early ethologist Oskar Heinroth, and studied scientifically and popularized by his disciple, Konrad Lorenz in his work with graylag geese. Lorenz demonstrated how incubator-hatched geese would imprint on the first suitable, moving stimulus they saw within what he called a "critical period" of about 36 hours shortly after hatching. Being present with the goslings during their hatching, Lorenz found that the goslings would imprint on himself. As a result of this, he is often depicted being followed by a gaggle of geese who had imprinted on him.
Sexual imprinting is the process by which a young animal learns the characteristics of a desirable mate. For example, male zebra finches appear to prefer mates with the appearance of the female bird that rears them, rather than mates of their own type (Immelmann 1972).
Reverse sexual imprinting is also observed when two people, living in close domestic proximity during the first few years of their lives, become desensitized to sexual attraction and bonding to each other later on. This phenomenon, known as the Westermarck effect, was discovered by anthropologist Edvard Westermarck. The Westermarck effect has since been observed in many places and cultures, including in the Israeli kibbutz system, and the Shim-pua marriage customs of Taiwan, as well as in biologically-related families.
When the opposite situation occurs, for example where a brother and sister are raised separately, not knowing about one another, they may find one another highly sexually attractive when they meet as adults—a phenomenon known as genetic sexual attraction. This observation is consistent with the theory that the Westermarck effect evolved to suppress inbreeding.
Evidence of imprinting in neuroscience
A structure associated with imprinting was located on either side of the brain in the hyperstratium ventrale (IMHV). By removing this part of the brain from chicks, Horn (1985) demonstrated that the chicks no longer displayed imprinting tendencies. The hyperstratium ventrale is a part of the dorsal ventrical ridge (DVR), a common brain structure found in both reptiles and birds. The dorsal ventrical ridge has also been shown to operate in a similar fashion to mammals' memory mechanisms.
Other research has questioned whether Lorenz's account of imprinting may be somewhat incomplete. Studying the birds in their natural environment, it is argued that Lorenz lacked the objectivity that can be facilitated in a laboratory. The experimental approach of modern research has allowed for understanding of the specific learning processes that ultimately contribute to the behavior of imprinting.
With more controlled environments, it has been found that the release of endorphins in the brain, providing comforting feedback, is part of the process. Other laboratory evidence suggest that imprinting is a form of associative learning, not entirely instinctual, and may take place over longer periods of time and in more species than have been observed in natural settings.
Knowledge of the imprinting process has been put to good use in situations where young have been raised in captivity without the presence of adults of their species. Caregivers for birds hatched in captivity have developed techniques to teach them survival skills, based on using the imprinting process to cause the young to identify with humans (often disguised to mimic the colors and patterns of the adult birds) and so follow them, mimicking their behavior.
The Italian hang glider pilot Angelo d'Arrigo manipulated Lorenz's technique to re-introduce threatened species of raptors into the wild. D'Arrigo noted that the flight of a non-motorized hang glider is very similar to the flight patterns of migratory birds, since both use updrafts of thermal currents to gain altitude, permitting soaring flight over long distances. Birds hatched in captivity have no mentor birds to teach them their traditional migratory routes. D'Arrigo hatched chicks under the wing of his glider, and they imprinted on him. Subsequently, he taught the fledglings to fly and to hunt. The young birds followed him not only on the ground (as with Lorenz), but also in the air as he took the path of various migratory routes. He flew across the Sahara and over the Mediterranean Sea to Sicily with eagles, from Siberia to Iran with a flock of Siberian cranes, and over Mount Everest with Nepalese eagles. His wife continues his work of re-introducing a breeding pair of condors into their South American habitat.
In a project similar to d'Arrigo's efforts, orphaned Canadian Geese were trained to their normal migration route by the Canadian ultralight enthusiast Bill Lishman, as shown in the fact-based dramatic film, Fly Away Home.
Imprinting is an intriguing phenomenon, as it is the product of both genetic and environmental influences. It seems evident that the young of any creature should possess the ability to ensure their survival. Imprinting is an essential bond between the parent and their newborn, as it enables them to learn necessary skills and to secure their well-being during potentially dangerous times. Such imprinting is most obvious in nidifugous birds and reptiles, and is clearly an advantageous process since young that leave the nest early on are at great risk in unable to find its parents.
Sexual imprinting also can be understood as valuable in the survival of the species, allowing young to identify characteristics of appropriate potential mates.
Imprinting can also occur in mammals, albeit in somewhat different forms and involving more prolonged and complex forms of interaction. In the study of child development, the related process by which babies learn to distinguish their mothers, or caregivers, is known as attachment. The process begins in the womb, when an unborn baby starts to recognize the parent's voices, and continues as there is a strong parent-child bond that deepens through lengthier, more complex processes.
- Horn, Gabriel. 1985. Memory, Imprinting, and the Brain. Oxford: Clarendon Press.
- Hoffman, Howard S. 1996. Imprinting. Retrieved August 21, 2008.
- Immelmann, K. 1972. Sexual and other long-term aspects of imprinting in birds and other species. Advances in the Study of Behavior 4: 147–174.
- Westermarck, Edward A. 1921. The History of Human Marriage, 5th ed. London: Macmillan.
- Angelo d'Arrigo personal website. Retrieved September 17, 2007.
- Debra Lieberman, John Tooby and Leda Cosmides. "Does morality have a biological basis? An empirical test of the factors governing moral sentiments relating to incest." Accepted for publication in Proc. R. Soc. Lond. B November 2002. Available online at Citeseer. Retrieved September 17, 2007.
- Cardoso, SH and Sabbatini, RME. Learning who is your mother. The behavior of imprinting. Brain & Mind Magazine. Retrieved September 17, 2007.
- Nancy T. Burley, a researcher into imprinting in zebra finches. Retrieved September 17, 2007.
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