Imprinting and Establishment of Ethology

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Imprinting and Establishment of Ethology

Overview

Although the term "ethology" dates back to 1859, it was only in the first half of the twentieth century that ethology—the systematic study of the function and evolution of behavior—expanded to become a recognized field of research. A key part of the development of this field was the widely recognized work of a number of animal behaviorists, notably zoologists Konrad Lorenz (1903-1989) of Austria, and Nikolaas Tinbergen (1907-1988) of the Netherlands. Lorenz gained prominence for his concept of filial imprinting, in which newly hatched geese will accept as their mother the first animal they see—even if that animal is a member of another species. Tinbergen is known for his research into the control and function of various animal behaviors. The two men, along with Austrian beecommunication researcher Karl von Frisch (1886-1982), shared the Nobel Prize in 1973 for their behavioral studies.

Background

At the turn of the century, the study of animal behavior was in its infancy. Animal behavior was not a cohesive and strong field on its own, but rather an outgrowth of numerous other disciplines, such as entomology or ornithology. As stated by Tinbergen in the foreword to The Oxford Companion to Animal Behavior (1987): "Biologists of my generation still remember the time when the study of animal behavior was not yet really accepted as a part of modern science, and was practiced by no more than a handful of individuals, who indulged in it either as a hobby or as a sideline to their 'real' work."

Lorenz, Tinbergen, Frisch, and others changed that viewpoint with their well-designed and provocative studies of animal behavior. One of these important research projects was a study of greylag geese by Lorenz. From 1935-38, he conducted field experiments of these birds and developed his concept of imprinting. For this work, he hatched goslings and presented himself to the goslings as they emerged from their shells. With the biological parents gone, the goslings fully accepted Lorenz as their mother, following him and calling him just as they would with their real mother. He later discovered that the goslings would accept any moving object as their foster mother, provided it was the first object they saw upon hatching. He called this behavior "imprinting." (Research in later years has indicated that some birds will even imprint on unmoving objects, provided they are of a color contrasting that of the environment.) Lorenz also identified this behavior in mallard ducks. In order to get the ducks to imprint on him, however, he also had to quack and squat so he was closer to their height. Through his work, he was able to demonstrate that imprinting occurred only during a very short time span, called a sensitive period.

In addition, Lorenz found that imprinting affected the goslings' and ducklings' selection of mates later in life. His research indicated that when certain animals are reared by foster parents of second species, the animals will approach members of the second species as mates when they mature. Even when these sexually imprinted animals were placed with members of their own species and eventually mated with them, they retained their imprinted preferences and, when given the choice, still approached the second species over their own. Sexual imprinting does not occur in all species, however. Cowbirds and cuckoos, for instance, typically lay their eggs in the nests of other birds, which then rear the young as their own. In the cases of these and other brood parasites, the young birds do not sexually imprint on the foster-parent species.

Tinbergen's studies of animal behavior extended from birds to insects. For his doctoral research, for example, he observed and dissected the behavior of digger wasps, and attempted to determine the causes of distinct activities. While conducting this work, he noted that each female wasp was able to pick out her own individual nest from the numerous nests located nearby. He then looked at the stimulus that keyed the female to the correct nest, and through various experiments, showed that the female located her nest via the tell-tale landmarks surrounding it. In addition, he found that the wasps identified their prey, which are honey bees, by first approaching an appropriately sized and moving object, then verifying that the target had the correct honey-bee odor, and finally gaining affirmation of its identity through either visual or tactile stimuli. Through this work, Tinbergen demonstrated the importance of distinct stimuli in triggering specific responses.

Influenced by other animal behaviorists, and in particular Oskar Heinroth (1871-1945), Lorenz and Tinbergen collaborated in the mid-1930s to flesh out the foundations of the emerging field of ethology, and promoted the field through their later writings.

Impact

The research of various animal behaviorists set the stage for the separate discipline of ethology. Oskar Heinroth made early contributions with his 1910-11 Ethology of the Anatidae, which discussed similarities and differences in the behaviors of different duck and goose species. Like Lorenz, he also observed imprinting in greylag geese.

Lorenz's work on imprinting identified irreversible patterns of behavior and illustrated the importance of learning in animal development. It also opened the doors to a wide array of studies on many animals, including humans, concerning the importance of exposure to various stimuli during the early stages of life. These topics, including the evolutionary processes that lead to the presence or absence of imprinting, are still very active areas of research today.

Lorenz expanded his ideas with a 1935 paper in which he described how the action of one individual can spark a separate action in another individual, and so on, so that a series of behaviors occur among the individuals in a group. The triggering action is called a releaser, and the responding action is called an innate releasing mechanism. Tinbergen also conducted research to expand this hypothesis. Tinbergen and Lorenz collaborated on a variety of studies, with Lorenz typically coming up with the ideas and Tinbergen designing experiments to test them. One of these collaborations led to their notion of fixed action patterns, in which animals follow a specific set of behaviors in response to environmental cues. For example, they found that the red spot on a mother gull's bill prompts the young to peck at the red spot. This, in turn, triggers the mother to regurgitate food to the waiting young.

Combined, the work of Lorenz and Tinbergen promoted discussion by scientists of many disciplines about the instinct-mediated learning and genetically driven motor skills present in many species of animals. Their descriptions and discussions of this complexity in behavior was a catalyst for other researchers to consider the effects of releasers, innate releasing mechanisms, and fixed action patterns specifically, as well as genetics and evolution on a broader level.

Tinbergen's 1951 book, The Study of Instinct, became the first comprehensive introduction to and review of ethology to be printed in English. The book is often credited with launching the new field into the prominence it enjoys today. Another book of note was Lorenz's On Aggression. In this popular though controversial 1966 publication, Lorenz began to apply to humans what he had learned about behavior from other animals. He considered whether humans share the causes for their aggressive behaviors with other animals. He offered the supposition that human aggression was an instinctive means of survival, and one that had become particularly dangerous, because weapons had developed faster than humans could adapt behaviorally to counteract their potential consequences.

Other scientists, too, saw connections between animal behavior and human psychology, and began to consider whether some of the ethologists' findings were applicable to humans. For example, scientists today are still debating whether human infants have a "sensitive period" when they are highly susceptible to stimuli from the environment, and if so, whether stimuli in infancy can have an effect on how smart, how creative, or how musically inclined a child will become later in life.

Because of the work of Lorenz, Tinbergen, Heinroth, and many others early in the twentieth century, ethology became a discipline of its own by the 1940s. Several universities began creating separate faculty positions in animal behavior, and many new students enrolled in animal-behavior courses and programs. By the 1950s, ethology had become a dynamic and almost multidisciplinary field. As Tinbergen noted in The Oxford Companion to Animal Behavior, students in this discipline read the work of and collaborated with psychologists, physiologists, ecologists, evolutionists, and even human sociologists in attempting to gain a broader understanding of animal behavior. He added, "As a consequence, the study of animal (and human) behavior has now become a vast cooperative effort, in which both specialization and collaboration with related sciences have their parts to play."

In 1973, Lorenz, Tinbergen, and Karl von Frisch, who made groundbreaking findings about the communication system in honey bees, shared the Nobel Prize in physiology or medicine for "their discoveries concerning organization of individual and social behavior patterns."

LESLIE A. MERTZ