Ethology

Abstract

Ethology is the branch of the behavioral sciences that studies animal behavior from a biological standpoint, observing it in the natural environment and asking not only how it works but what it is for and how it evolved. It emerged in the mid-twentieth century from the fieldwork of Konrad Lorenz, Nikolaas Tinbergen, and Karl von Frisch, who treated behavior as a product of evolution, to be described as carefully as anatomy. This article sets out its core ideas: the ethogram and the fixed action pattern, the sign stimulus that releases it, the four complementary questions Tinbergen posed of any behavior, the sensitive period of imprinting, and referential signals. Three interactive demonstrations let the reader release a fixed action pattern, trace the sensitive period for imprinting, and weigh the survival value of a predator-specific alarm call.

Keywords: ethology, fixed action pattern, imprinting

Ethology is the study of animal behavior as a biological phenomenon: something that has a physiological cause, a course of development, a function that bears on survival and reproduction, and an evolutionary history. Its defining commitment is to observe animals doing what they naturally do, in the settings to which they are adapted, before bringing them into the laboratory, and to treat every behavior pattern as a trait shaped by natural selection. This posture set ethology apart from the comparative psychology of its day, which studied a few convenient species at artificial tasks in the laboratory and sought general laws of learning. Where the psychologist asked how an animal learns, the ethologist asked first what the animal is built to do, and the answer began with patient description. The founding statement of the field was Tinbergen's insistence that ethology is the biological study of behavior, answerable to the same standards of observation and experiment as the rest of zoology (Tinbergen, 1963).

What Ethology Is

Ethology is best understood by its questions and its method rather than by a list of animals or behaviors. The method is naturalistic observation disciplined by experiment: the ethologist begins by compiling an ethogram, a complete catalogue of the behavior patterns a species performs, and only then designs experiments that manipulate the natural situation to isolate what causes a behavior and what it accomplishes. The questions are biological. A behavior, for the ethologist, is a phenotype like a bone or an enzyme, produced by machinery inside the animal, assembled over the course of development, maintained in the population because it contributes to survival and reproduction, and inherited from ancestors in modified form. This is why ethology grew up inside zoology rather than psychology, and why its founders drew their examples from the courtship of sticklebacks, the egg-retrieval of geese, and the dance of honeybees rather than from rats in mazes. The discipline crystallized around the conviction, argued forcefully by Konrad Lorenz, that behavior evolves in the same way morphology does and can be used, like a shared bone, to reconstruct the evolutionary relationships among species (Lorenz, 1958). That conviction gave the field a research program: describe behavior exactly, find its immediate triggers, and explain both its function and its phylogeny.

The Founding of Ethology

Modern ethology has three founders, and the 1973 Nobel Prize in Physiology or Medicine that they shared marked the moment biology formally recognized behavior as its subject. Konrad Lorenz, working in Austria, supplied much of the early conceptual vocabulary, including the fixed action pattern, the innate releasing mechanism, and imprinting, and he championed the comparative method that treats behavior as evolved. Nikolaas Tinbergen, a Dutch biologist who later built a research school at Oxford, supplied the experimental rigor, devising elegant field experiments that tested ethological ideas against nature rather than merely illustrating them. Karl von Frisch, in Munich, decoded the waggle dance of the honeybee, showing that a returning forager communicates the direction and distance of a food source to her nestmates through a symbolic movement, one of the first demonstrations that a non-human animal transmits abstract information. The three brought complementary strengths, and the field they founded fused careful description, evolutionary reasoning, and controlled experiment into a single enterprise. The history of that fusion, and of the tangled relations between Lorenz and Tinbergen across the upheavals of the mid-century, has been documented in detail by later historians of the discipline (Burkhardt, 2005). What unites the founders is a single methodological insistence, most clearly voiced by Tinbergen: that a science of behavior must ask, and keep distinct, several different kinds of question at once (Tinbergen, 1963).

Fixed Action Patterns and Sign Stimuli

The classical unit of ethological analysis is the fixed action pattern: a stereotyped, species-typical sequence of movements that, once triggered, runs to completion in much the same form every time, even if the stimulus that started it is removed. A greylag goose that sees an egg outside its nest will rise, extend its neck, and roll the egg back with the underside of its bill; remove the egg mid-roll and the goose completes the retrieving movement over empty ground. What triggers such a pattern is not the whole object but a sign stimulus, a specific and often surprisingly simple feature that the animal's nervous system is tuned to detect. Lorenz and Tinbergen proposed that a dedicated innate releasing mechanism links the sign stimulus to the motor pattern, so that the right key opens a fixed behavioral lock (Tinbergen, 1951). A male three-spined stickleback attacks other males not because it recognizes a rival but because it detects the red belly they display in the breeding season; crude models with a red underside draw more attack than an accurate stickleback model without one. The most striking evidence that the animal responds to an isolated feature rather than the natural object is the supernormal stimulus: an exaggerated dummy that exceeds the natural releaser on the relevant dimension can elicit a stronger response than the real thing, as when a bird will preferentially try to retrieve an artificially enormous egg in place of its own. The demonstration below lets the reader vary the redness and size of a herring gull's bill spot, the sign stimulus that releases pecking in the chick, and watch the response climb into the supernormal range.

Tinbergen's Four Questions

Ethology's most enduring contribution to the whole of biology is a simple observation about explanation: any behavior can be explained in four different and complementary ways, and the explanations do not compete. Tinbergen distinguished the behavior's mechanism, meaning the physiological and perceptual machinery that produces it here and now; its development, meaning how it is assembled over the life of the individual; its function, meaning the survival or reproductive advantage that keeps it in the population; and its evolution, meaning the phylogenetic history through which it arose (Tinbergen, 1963). The first two are proximate questions, about how a behavior works; the last two are ultimate questions, about why it exists. A full account of birdsong answers all four: the neural song system and hormones that generate the song, the mix of inherited template and tutor learning by which a young bird acquires it, the mate attraction and territory defense it serves, and the ancestral vocalizations from which it descends. Many apparent disputes in the study of behavior dissolve once one notices that the antagonists are answering different questions. The framework has proved durable enough that later biologists have refined rather than replaced it, sharpening in particular the line between the proximate causes of Tinbergen's first two questions and the ultimate, evolutionary causes of the last two, and warning against the common error of treating an answer at one level as if it excluded the others (Bateson & Laland, 2013).

Figure 1

Tinbergen's Four Questions as a Two-by-Two of Explanatory Levels

Imprinting and the Sensitive Period

Nothing did more to dissolve the old opposition between innate and learned behavior than the ethological study of imprinting. Lorenz famously observed that a newly hatched greylag gosling will follow and become socially attached to the first conspicuous moving object it encounters, ordinarily its mother but, in his experiments, Lorenz himself. Filial imprinting of this kind is most evident in precocial species, which hatch mobile and open-eyed and must identify a parent to follow at once, rather than in altricial species whose young are born helpless and tended in a nest. Imprinting is neither a simple reflex nor ordinary learning. It is a learning process, because the young animal acquires the specific features of whatever it imprints on, yet it is constrained by biology in ways ordinary learning is not: it occurs only during a sensitive period early in life, it requires little or no reinforcement, and once formed it is highly resistant to change. The systematic experimental analysis of these properties, distinguishing the timing of the sensitive period, the stimuli that are effective, and the conditions under which the attachment can be reversed, was carried out in the 1960s and after, and it revealed imprinting to be a graded and interactive process rather than the instantaneous stamping the metaphor suggests (Bateson, 1966). Imprinting matters beyond its own case because it is the clearest instance of a general ethological truth: development is a collaboration between an inherited predisposition and the experience that arrives on a biological timetable, so the question is never whether a behavior is innate or learned but how the two are woven together. That conclusion was forced in part by a sharp critique from comparative psychology. Daniel Lehrman argued that Lorenz's notion of innate behavior explained nothing, because to call a behavior inherited merely relabels the developmental process that actually has to be traced, and the debate that followed pushed ethology toward the interactionist analysis of development it holds today (Lehrman, 1953). The demonstration below traces how the strength of filial imprinting depends on the age at which a precocial bird first meets a moving object, peaking within a sensitive window and falling away on either side.

Communication and Referential Signals

Animals signal to one another constantly, in postures, colors, calls, and movements, and ethology asks what these signals mean and what they are for. Many signals evolved from other behavior by a process Tinbergen called ritualization, in which an incidental movement, a preparatory intention movement or a displacement activity performed under conflict, becomes exaggerated, stereotyped, and emancipated from its original cause to serve as a display (Tinbergen, 1952). The deepest question about animal signals is whether they carry information about the world or merely broadcast the signaler's arousal. The classic answer came from the vervet monkey. Vervets give acoustically distinct alarm calls for their three main predators, and each call elicits a different and appropriate escape: the leopard call sends the troop into the trees, the eagle call makes them look up and dash into cover, and the snake call makes them stand and scan the ground. Because the calls can be played back from a hidden speaker with no predator present and still produce the correct, predator-specific response, they function as referential signals that designate a class of danger rather than simply expressing fear (Seyfarth et al., 1980). Table 1 sets out the three calls, the predator each specifies, and the distinct escape it elicits. Signaling is also embedded in the wider social life of animals, whose group living brings benefits of defense and information but also costs, including the faster spread of parasites and disease through a well-connected society, a trade-off that shapes how sociality itself evolves (Kappeler et al., 2015). The demonstration below lets the reader sound each vervet alarm and see why a predator-specific signal is worth far more to the receiver than an undifferentiated cry of alarm.

Worked Example

Why should a signal specify which predator is present rather than simply announce danger? The value of reference can be made exact with a small survival model. Suppose a vervet troop faces three predators with different frequencies: a leopard on 50 percent of encounters, an eagle on 30 percent, and a snake on 20 percent. For each predator there is one correct escape, and taking it yields a high survival probability: 0.90 against the leopard, 0.85 against the eagle, and 0.80 against the snake. A predator-specific alarm call always cues the correct escape, so the expected survival per encounter under referential calling is the weighted average 0.50 times 0.90 plus 0.30 times 0.85 plus 0.20 times 0.80, which is 0.45 plus 0.255 plus 0.16, or 0.865.

Now suppose instead the troop had only a single undifferentiated alarm call. A monkey hearing it knows danger is near but not which escape to make, and must in effect guess among the three responses, one of which is right and two of which are wrong. Taking the wrong escape is dangerous: fleeing into a tree is fatal against an eagle, which hunts from above. Let the survival probabilities for a wrong escape be 0.30 against the leopard, 0.25 against the eagle, and 0.40 against the snake. With a one-in-three chance of the correct response, expected survival against the leopard is one third of 0.90 plus two thirds of 0.30, which is 0.50; against the eagle, one third of 0.85 plus two thirds of 0.25, which is about 0.45; and against the snake, one third of 0.80 plus two thirds of 0.40, which is about 0.53. Weighting these by predator frequency gives 0.50 times 0.50 plus 0.30 times 0.45 plus 0.20 times 0.53, or about 0.49.

The referential system therefore raises expected survival from roughly 0.49 to 0.865 per predator encounter, an advantage of about 37 percentage points. That difference, compounded across the many encounters of a lifetime, is a powerful selection pressure favoring calls that classify the threat, and it explains why a signal that names the danger can be so richly rewarded by natural selection (Seyfarth et al., 1980). The numbers here are illustrative rather than measured, but the structure is general: reference pays whenever different situations demand different responses and the cost of the wrong response is high.

Discussion

Ethology transformed the study of behavior by insisting that behavior is biology and must be explained as evolution explains everything else, and its central ideas have long since diffused into psychology, neuroscience, and behavioral ecology. The fixed action pattern and the sign stimulus gave a rigorous vocabulary for species-typical behavior; imprinting dismantled the innate-versus-learned dichotomy and replaced it with a developmental account; and Tinbergen's four questions supplied a framework for keeping distinct explanations from being mistaken for rivals. The discipline's boldest and most contested extension concerns the animal mind. Donald Griffin argued that the machinery of behavior does not exhaust its subject and that the possibility of animal awareness deserves scientific study rather than dismissal, launching the program of cognitive ethology (Griffin, 1976). The claim remains difficult, because consciousness in another species is not directly observable, and a strand of contemporary work argues that the practical questions ethology can actually answer, about what an animal needs and whether those needs are met, can and should be addressed through behavior and physiology without first settling the intractable question of subjective experience (Dawkins, 2017). The tension is a productive one. What is not in doubt is the field's founding wager, now thoroughly vindicated: that the behavior of animals is as lawful, as evolved, and as open to disciplined study as any structure in the body, and that watching animals carefully in the world they are built for is where that study begins.

Current Directions

Contemporary ethology has moved well beyond its classical concerns while keeping their evolutionary frame. One major current is the biology of animal culture. Long-term field studies of great apes have documented behavioral traditions, from tool techniques to social customs, that vary between populations, are transmitted by social learning rather than genetics, and satisfy the criteria for culture, extending the reach of evolutionary biology into a domain once thought uniquely human (Whiten, 2017). A second current runs into molecular biology. The old category of instinct is being reopened by work on how genes and experience jointly build behavior, with epigenetic mechanisms, the chemical marks that switch genes on and off without altering the DNA sequence, emerging as a route by which the environment tunes the developmental programs that produce species-typical behavior (Robinson & Barron, 2017). A third current turns the comparative method on the human animal. The tools of ethology and comparative cognition are increasingly used to ask precisely what, if anything, is unique about human minds, isolating the specific cognitive capacities, in social learning, teaching, and cumulative culture, that distinguish our species against the backdrop of its close relatives (Laland & Seed, 2021). Together these directions describe a field that has kept Tinbergen's four questions as its scaffold while pushing outward to culture, to molecules, and to the evolutionary origins of human cognition itself.

Common Misconceptions

Ethology is just anecdotal nature watching, not real experimental science.

Observation is where ethology starts, not where it stops. Its founders built precise field and laboratory experiments, isolating the single feature that releases a behavior with dummy stimuli and testing signal meaning with hidden-speaker playbacks, and the field holds its claims to the same evidentiary standard as the rest of biology (Tinbergen, 1951).

A behavior is either innate or learned.

This dichotomy is exactly what ethology dismantled. Imprinting is a learning process that is nonetheless constrained by an inherited timetable and predisposition, and modern work shows genes and experience interacting through epigenetic mechanisms; the real question is always how nature and nurture are woven together, not which one acts alone (Robinson & Barron, 2017).

Imprinting happens instantly and can never be undone.

Experimental analysis shows imprinting to be graded rather than all-or-none: its strength depends on the age at exposure and on the amount of experience, it is confined to a sensitive period rather than a single instant, and under some conditions it can be partly reversed. The stamping metaphor overstates a real but limited constraint (Bateson, 1966).

Animal alarm calls are just involuntary expressions of fear.

Some signals do broadcast arousal, but not all. Vervet alarm calls are predator-specific and elicit the appropriate escape even when played from a hidden speaker with no predator present, which means the call designates a class of danger rather than merely venting emotion, and functions as a genuinely referential signal (Seyfarth et al., 1980).

Glossary

Altricial.

Born or hatched in a helpless, undeveloped state and dependent on parental care, as in songbirds and humans; contrasted with precocial.

Cognitive ethology.

The study, initiated by Donald Griffin, of the mental experiences and awareness of animals as a legitimate biological question.

Displacement activity.

An apparently irrelevant behavior, such as preening or grooming, performed when an animal is caught between conflicting drives; a common evolutionary source of signals.

Ethogram.

A systematic catalogue of all the behavior patterns a species performs, the descriptive foundation of any ethological study.

Ethology.

The biological study of animal behavior in its natural context, emphasizing its mechanism, development, function, and evolution.

Fixed action pattern.

A stereotyped, species-typical sequence of movements that, once released, runs to completion in a constant form even if the triggering stimulus is removed.

Imprinting.

A form of learning, confined to a sensitive period early in life, by which a young animal forms a lasting attachment to a parent, object, or class of individuals.

Innate releasing mechanism.

The hypothesized perceptual filter that detects a sign stimulus and, in response, releases the corresponding fixed action pattern.

Instinct.

A traditional term for inherited, species-typical behavior that develops reliably without specific training; now understood as the product of interacting genes and experience.

Precocial.

Born or hatched in a relatively mature, mobile state, as in geese and ducks, the condition in which filial imprinting is most clearly seen.

Proximate cause.

An explanation of a behavior in terms of its immediate mechanism or its development, answering how the behavior works.

Referential signal.

A communication signal that designates a specific external object or event, such as a predator-specific alarm call, rather than merely expressing the signaler's internal state.

Ritualization.

The evolutionary process by which an ordinary movement becomes exaggerated and stereotyped into a communicative display.

Sensitive period.

A limited window in development during which a particular experience, such as the object of imprinting, has its greatest and most lasting effect.

Sign stimulus.

A specific feature of an object or situation that, on its own, releases a fixed action pattern; also called a releaser when it functions in communication.

Supernormal stimulus.

An exaggerated version of a sign stimulus that elicits a stronger response than the natural stimulus does, revealing which feature the animal is tuned to.

Ultimate cause.

An explanation of a behavior in terms of its function or its evolutionary history, answering why the behavior exists.

Key Researchers

Marian Stamp Dawkins (b. 1945). Ethologist at the University of Oxford; her work on animal welfare argues that the questions of what animals need and whether those needs are met can be answered behaviorally, without first resolving the problem of animal consciousness. Faculty Page - ORCID - Wikipedia

Karl von Frisch (1886-1982). Ethologist at the University of Munich and Nobel laureate; he decoded the honeybee waggle dance, showing that a forager communicates the direction and distance of food to her nestmates. Wikipedia - Wikidata

Donald R. Griffin (1915-2003). Zoologist at Rockefeller University; he discovered echolocation in bats and later founded cognitive ethology, arguing that animal awareness is a proper subject of biological study. Wikipedia - Wikidata

Robert A. Hinde (1923-2016). Ethologist at the University of Cambridge; he integrated ethology with developmental and comparative psychology and mentored a generation of researchers studying behavior and social relationships. Wikipedia - Wikidata

Kevin N. Laland. Evolutionary biologist at the University of St Andrews; his work on social learning, niche construction, and cultural evolution has helped update the ethological account of how behavior develops and evolves. Faculty Page - ORCID - Wikipedia

Konrad Lorenz (1903-1989). One of the founders of ethology and a Nobel laureate; he introduced the fixed action pattern, the innate releasing mechanism, and imprinting, and championed the comparative study of behavior as evolved. Wikipedia - Wikidata

Nikolaas Tinbergen (1907-1988). Ethologist at the University of Oxford and Nobel laureate; his four questions gave biology its canonical statement of complementary levels of explanation, and his field experiments set the discipline's methodological standard. Wikipedia - Wikidata

Andrew Whiten. Psychologist at the University of St Andrews; his long-term studies of social learning and traditions in great apes established that animal culture is real and extends the scope of evolutionary biology. Faculty Page - ORCID - Wikidata

Frequently Asked Questions

What is ethology?
Ethology is the biological study of animal behavior, especially behavior observed in the natural environment to which a species is adapted. It treats each behavior pattern as an evolved trait and asks four kinds of question about it: how it works, how it develops, what it is for, and how it evolved (Tinbergen, 1963).

How does ethology differ from comparative psychology?
The two fields both study animal behavior but grew from different roots. Comparative psychology arose within psychology and traditionally studied a few species at controlled laboratory tasks, seeking general laws of learning, whereas ethology arose within zoology and began from naturalistic observation of species-typical behavior in the wild, emphasizing evolution and function. The traditions have largely converged in modern behavioral science.

What are Tinbergen's four questions?
They are the four complementary explanations any behavior can be given: its mechanism (the machinery that produces it), its development (how it is assembled over a lifetime), its function (the survival or reproductive advantage it confers), and its evolution (its phylogenetic history). The first two are proximate and the last two are ultimate (Tinbergen, 1963).

What is a fixed action pattern?
A fixed action pattern is a stereotyped, species-typical sequence of movements that runs to completion once triggered, even if the triggering stimulus is removed partway through. It is released by a specific sign stimulus rather than by the whole natural object, as when a goose completes an egg-rolling movement over empty ground (Tinbergen, 1951).

What is imprinting?
Imprinting is a special form of learning, confined to a sensitive period early in life, through which a young animal forms a lasting attachment, most famously the following response of a newly hatched gosling to the first moving object it sees. It requires little reinforcement and is highly resistant to later change, though experimental work shows it is graded rather than all-or-none (Bateson, 1966).

Are animal alarm calls a kind of language?
They share one important feature with language, reference, but not the full system. Vervet monkeys give distinct alarm calls for different predators, and each cues the appropriate escape even when played from a hidden speaker, so the calls designate an external category of danger rather than merely expressing fear. They lack the open-ended grammar of human language, but they are genuinely informative (Seyfarth et al., 1980).

Who founded ethology?
Modern ethology was founded by Konrad Lorenz, Nikolaas Tinbergen, and Karl von Frisch, who shared the 1973 Nobel Prize in Physiology or Medicine for their discoveries about the organization and elicitation of behavior. Lorenz supplied much of the theory, Tinbergen the experimental method, and von Frisch the decoding of honeybee communication (Lorenz, 1958).

Is ethology still an active field?
Yes. Its framework underlies modern behavioral ecology and comparative cognition, and current research applies ethological methods to animal culture in great apes, to the epigenetic basis of instinct, and to the evolutionary origins of human cognition (Whiten, 2017).

References

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Burkhardt, R. W., Jr. (2005). Patterns of behavior: Konrad Lorenz, Niko Tinbergen, and the founding of ethology. University of Chicago Press.

Dawkins, M. S. (2017). Animal welfare with and without consciousness. Journal of Zoology, 301(1), 1-10. https://doi.org/10.1111/jzo.12434

Griffin, D. R. (1976). The question of animal awareness: Evolutionary continuity of mental experience. Rockefeller University Press.

Kappeler, P. M., Cremer, S., & Nunn, C. L. (2015). Sociality and health: Impacts of sociality on disease susceptibility and transmission in animal and human societies. Philosophical Transactions of the Royal Society B, 370(1669), 20140116. https://doi.org/10.1098/rstb.2014.0116

Laland, K. N., & Seed, A. M. (2021). Understanding human cognitive uniqueness. Annual Review of Psychology, 72, 689-716. https://doi.org/10.1146/annurev-psych-062220-051256

Lehrman, D. S. (1953). A critique of Konrad Lorenz's theory of instinctive behavior. The Quarterly Review of Biology, 28(4), 337-363. https://doi.org/10.1086/399858

Lorenz, K. Z. (1958). The evolution of behavior. Scientific American, 199(6), 67-78. https://doi.org/10.1038/scientificamerican1258-67

Robinson, G. E., & Barron, A. B. (2017). Epigenetics and the evolution of instincts. Science, 356(6333), 26-27. https://doi.org/10.1126/science.aam6142

Seyfarth, R. M., Cheney, D. L., & Marler, P. (1980). Monkey responses to three different alarm calls: Evidence of predator classification and semantic communication. Science, 210(4471), 801-803. https://doi.org/10.1126/science.7433999

Tinbergen, N. (1951). The study of instinct. Clarendon Press.

Tinbergen, N. (1952). "Derived" activities: Their causation, biological significance, origin, and emancipation during evolution. The Quarterly Review of Biology, 27(1), 1-32. https://doi.org/10.1086/398642

Tinbergen, N. (1963). On aims and methods of ethology. Zeitschrift fur Tierpsychologie, 20(4), 410-433. https://doi.org/10.1111/j.1439-0310.1963.tb01161.x

Whiten, A. (2017). Culture extends the scope of evolutionary biology in the great apes. Proceedings of the National Academy of Sciences, 114(30), 7790-7797. https://doi.org/10.1073/pnas.1620733114