What is imprinting?

Introduction

Imprinting is an important type of behavior by which an animal learns specific concepts and identifies certain objects or individuals that are essential for survival. Imprinting events almost always occur very early in the life of an animal, during critical periods or time frames when the animal is most sensitive to environmental cues and influences. The phenomenon occurs in a variety of species, but it is most pronounced in the homeothermic (warm-blooded) and socially oriented higher vertebrate species, especially mammals and birds.

Imprinting is learned behavior. Most learned behavior falls within the domain of exogenous behavior, or behavior that an animal obtains by its experiences with fellow conspecifics (members of the same species) and the environment. Imprinting, however, is predominantly, if not exclusively, an endogenous behavior
, which is a behavior that is genetically encoded within the individual. An individual is born with the capacity to imprint. The animal’s cellular biochemistry and physiology will determine when in its development the imprinting will occur. The only environmental influence of any consequence in imprinting is the object of the imprint during the critical period. Ethologists, scientists who study animal behavior, debate the extent of endogenous and exogenous influences on animal behavior. Most behaviors involve a combination of both, although one type may be more pronounced than the other.

The capacity for an animal to imprint is genetically determined and, therefore, is inherited. This type of behavior is to the animal’s advantage for critical situations that must be correctly handled the first time they occur. Such behaviors include the identification of one’s parents (especially one’s mother), the ability to navigate, the ability to identify danger, and even the tendency to perform the language of one’s own species. Imprinting behaviors generally are of high survival value and hence must be programmed into the individual via the genes. Biological research has failed to identify many of the genes that are responsible for imprinting behaviors, although the hormonal basis of imprinting is well understood. Most imprinting studies have focused on the environmental signals and developmental state of the individual during the occurrence of imprinting.

Maternal Imprinting

These studies have involved mammals and birds, warm-blooded species that have high social bonding, which seems to be a prerequisite for imprinting. The most famous imprinting studies were performed by the animal behaviorists and Nobel laureates Konrad Lorenz
and Nikolaas Tinbergen. They and their many colleagues detailed analyses of imprinting in a variety of species, in particular waterfowl such as geese and ducks. The maternal imprinting behavior of the newborn gosling or duckling on the first moving object that it sees is the most striking example of imprinting behavior.

The maternal imprint is the means by which a newborn identifies its mother and the mother identifies its young. In birds, the newborn chick follows the first moving object that it sees, an object that should be its mother. The critical imprinting period is within a few hours after hatching. The chick visually will lock on its moving mother and follow it wherever it goes until the chick reaches adulthood. The act of imprinting not only allows for the identification of one’s parents but also serves as a trigger for all subsequent social interactions with members of one’s own species. As has been established in numerous experiments, a newborn gosling that first sees a female duck will imprint on the duck and follow it endlessly. On reaching adulthood, the grown goose, which has been raised in the social environment of ducks, will attempt to behave as a duck, even to the point of mating. Newborn goslings, ducklings, and chicks can easily imprint on humans.

In mammals, imprinting relies not only on visual cues (specific visible physical objects or patterns that an animal learns to associate with certain concepts) but also on physical contact and smell. Newborn infants imprint on their mothers, and vice versa, by direct contact, sight, and smell during the critical period, which usually occurs within twenty hours following birth. The newborn and its mother must come into direct contact with each other’s skin and become familiarized with each other’s smell. The latter phenomenon involves the release of special hormones called pheromones from each individual’s body. Pheromones trigger a biochemical response in the body of the recipient individual, in this case leading to a locked identification pattern for the other involved individual. If direct contact between mother and infant is not maintained during the critical imprinting period, then the mother may reject the infant because she is unfamiliar with its scent. In such a case, the infant’s life would be in jeopardy unless it were claimed by a substitute mother. Even in this situation, the failure to imprint would trigger subsequent psychological trauma in the infant, possibly leading to aberrant social behavior in later life.

Bird Migration and Danger Recognition

Although maternal imprinting in mammal and bird species is the best-documented example of imprinting behavior, imprinting may be involved in other types of learned behavior. In migratory bird species, ethologists have attempted to explain how bird populations navigate from their summer nesting sites to their wintering sites and back every year without error. Different species manage to navigate in different fashions. The indigo bunting, for example, navigates via the patterns of stars in the sky at night. Indigo bunting chicks imprint on the celestial star patterns for their summer nesting site during a specific critical period, a fact that was determined by the rearrangement of planetarium stars for chicks by research scientists.

Further research studies on birds also implicate imprinting in danger recognition and identification of one’s species-specific call or song. Young birds of many species identify predatory birds, such as hawks, falcons, and owls, by the outline of the predator’s body during flight or attack and by special markings on the predator’s body. Experiments also have demonstrated that unhatched birds can hear their mother’s call or song; birds may imprint on their own species’ call or song before they hatch. These studies reiterate the fact that imprinting is associated with a critical period during early development in which survival-related behaviors must become firmly established.

Human Imprinting

Imprinting is of considerable interest to psychologists because of its role in the learning process for humans. Humans imprint in much the same fashion as other mammals. The extended lifetime, long childhood, and great capacity for learning and intelligence make imprinting in humans an important area of study. Active research on imprinting is continually being conducted with humans, primates, marine mammals (such as dolphins, whales, and seals), and many other mammals, as well as with a large variety of bird species. Comparisons among the behaviors of these many species yield considerable similarities in the mechanisms of imprinting. These similarities underscore the importance of imprinting events in the life, survival, and socialization of the individual.

With humans, maternal imprinting occurs much as with other mammals. The infant and its mother must be in direct contact during the hours following birth. During this critical period, there is an exchange of pheromones between mother and infant, an exchange that, to a large extent, will bond the two. Such bonding immediately following birth can occur between infant and father in the same manner. Many psychologists stress the importance of both parents being present at the time of a child’s delivery and making contact with the child during the critical hours of the first day following birth. Familiarization is important not only for the child but for the parents as well because all three are imprinting on one another.

Failure of maternal or paternal imprinting during the critical period following birth can have drastic consequences in humans. The necessary, and poorly understood, biochemical changes that occur in the bodies of a child and parent during the critical period will not occur if there is no direct contact and, therefore, no transfer of imprinting pheromones. Consequently, familiarization and acceptance between the involved individuals may not occur, even if intense contact is maintained after the end of the critical period. The psychological impact on the child and on the parents may be profound, perhaps not immediately, but in later years. Studies on this problem are extremely limited because of the difficulty of tracing cause-and-effect relationships over many years when many behaviors are involved. There is some evidence, however, that indicates that failure to imprint may be associated with such things as learning disabilities, child-parent conflicts, and abnormal adolescent behavior. Nevertheless, other cases of imprinting failure seem to have no effect, as can be seen in tens of thousands of adopted children. The success or failure of maternal imprinting in humans is a subject of considerable importance in terms of how maternal imprinting affects human behavior and social interactions in later life.

Different human cultures maintain distinct methods of child rearing. In some cultures, children are reared by family servants or relatives from birth onward, not by the mother. Some cultures wrap infants very tightly so that they can barely move; other cultures are more permissive. Child and adolescent psychology focuses attention on early life experiences that could have great influence on later social behavior. The success or failure of imprinting, along with other early childhood experiences, may be a factor in later social behaviors such as competitiveness, interaction with individuals of the opposite sex, mating, and maintenance of a stable family structure. Even criminal behavior and psychological abnormalities may be traceable to such early childhood events.

Experiments

Imprinting studies conducted with nonhuman mammals and bird species are much easier than those with humans because the researcher has the freedom to conduct controlled experiments that test many different variables, thereby identifying the factors that influence an individual animal’s ability to imprint. For bird species, a famous experiment is the moving ball experiment. A newly hatched chick is isolated in a chamber within which a suspended ball revolves around the center of the chamber. The researcher can test not only movement as an imprinting trigger but also other variables, such as critical imprinting time after hatching, color as an imprinting factor, and variations in the shape of the ball as imprinting factors. Other experiments involve switching eggs between different species (for example, placing a duck egg among geese eggs).

For mammals, imprinting has been observed in many species, such as humans, chimpanzees, gorillas, dolphins, elephant seals, wolves, and cattle. In most of these species, the failure of a mother to come into contact with its newborn almost always results in rejection of the child. In species such as elephant seals, smell is the primary means by which a mother identifies its pups. Maternal imprinting is of critical importance in a mammalian child’s subsequent social development. Replacement of a newborn monkey’s natural mother with a “doll” substitute leads to irreparable damage; the infant will be socially and sexually repressed in its later encounters with other monkeys. These and other studies establish imprinting as a required learning behavior for the successful survival and socialization of all birds and nonhuman mammals.

Biology and Behavior

Animal behaviorists and psychologists attempt to identify the key factors that are responsible for imprinting in mammalian and avian species. Numerous factors, including vocal cues (specific sounds, frequency, and language that an animal learns to associate with certain concepts) and visual cues, are probably involved, although the strongest two factors appear to be direct skin contact and the exchange of pheromones that are detectable by smell. The maternal imprinting behavior is the most intensively studied imprinting phenomenon, though imprinting appears to occur in diverse behaviors such as mating, migratory navigation, and certain forms of communication.

Imprinting attracts the interest of psychologists because it occurs at critical periods in an individual’s life; because subsequent developmental, social, and behavioral events hinge on what happens during the imprinting event; and because imprinting occurs at the genetic or biochemical level. Biochemically, imprinting relies on the production and release of pheromones, molecules that have a specific structure and that can be manufactured in the laboratory. The identification and mass production of these pheromones could possibly produce treatments for some behavioral abnormalities.

As an endogenous (instinctive) form of learning, imprinting relies on the highly complex nervous and endocrine systems of birds and mammals. It also appears limited to social behavior, a major characteristic of these species. The complex nervous systems involve a highly developed brain, vocal communication, well-developed eyes, and a keen sense of smell. The endocrine systems of these species produce a variety of hormones, including the pheromones that are involved in imprinting, mating, and territoriality. Understanding the nervous and endocrine regulation of behavior at all levels is of major interest to biological and psychological researchers. Such studies may prove to be fruitful in the discovery of the origin and nature of animal consciousness.

Imprinting may be contrasted with exogenous forms of learning. One type of exogenous learning is conditioning, in which individuals learn by repeated exposure to a stimulus, by association of the concept stimulus with apparently unrelated phenomena and objects, or by a system of reward and punishment administered by parents. Other exogenous learning forms include habituation (getting used to something) and trial and error. All learned behaviors are a combination of endogenous and exogenous factors.

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