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Ethology (from Greek: ἦθος, ethos, "character"; and -λογία, -logia, "the study of") is the scientific study of animal behavior, and a sub-topic of zoology.
Although many naturalists have studied aspects of animal behavior throughout history, the modern discipline of ethology is generally considered to have begun during the 1930s with the work of Dutch biologist Nikolaas Tinbergen and Austrian biologists Konrad Lorenz and Karl von Frisch, joint winners of the 1973 Nobel Prize in Physiology or Medicine.[1] Ethology is a combination of laboratory and field science, with a strong relation to certain other disciplines such as neuroanatomy, ecology, and evolution. Ethologists are typically interested in a behavioral process rather than in a particular animal group, and often study one type of behavior (e.g. aggression) in a number of unrelated animals.
The desire to understand animals has made ethology a rapidly growing field. Since the turn of the 21st century, many aspects of animal communication, animal emotions, animal culture, learning, and even sexual conduct that experts long thought they understood, have been reexamined, and new conclusions reached. New fields have developed, such as neuroethology.
The term ethology derives from the Greek word èthos (ήθος), meaning character. Other words that derive from ethos include ethics[2] and ethical. The term was first popularized by American myrmecologist William Morton Wheeler in 1902.[3] An earlier, slightly different sense of the term was proposed by John Stuart Mill in his 1843 System of Logic.[4] He recommended the development of a new science, "ethology," the purpose of which would be explanation of individual and national differences in character, on the basis of associationistic psychology. This use of the word was never adopted.
Comparative psychology also studies animal behaviour, but, as opposed to ethology, is construed as a sub-topic of psychology rather than as one of biology. Historically, where comparative psychology researches animal behaviour in the context of what is known about human psychology, ethology researches animal behaviour in the context of what is known about animal anatomy, physiology, neurobiology, and phylogenetic history. Furthermore, early comparative psychologists concentrated on the study of learning and tended to research behaviour in artificial situations, whereas early ethologists concentrated on behaviour in natural situations, tending to describe it as instinctive. The two approaches are complementary rather than competitive, but they do result in different perspectives and, sometimes, conflicts of opinion about matters of substance. In addition, for most of the twentieth century, comparative psychology developed most strongly in North America, while ethology was stronger in Europe. A practical difference is that early comparative psychologists concentrated on gaining extensive knowledge of the behaviour of very few species. Ethologists were more interested in understanding behaviour in a wide range of species to facilitate principled comparisons across taxonomic groups. Ethologists have made much more use of a truly comparative method than comparative psychologists have. Despite the historical divergence, most ethologists, at least in North America, teach in psychology departments. It is a strong belief among scientists that the mechanisms on which behavioural processes are based are the same that cause the evolution of the living species: there is therefore a strong association between these two fields.
Until the 19th century, the most common theory among scientists was still the concept of scala naturae, proposed by Aristotle. According to this theory, living beings were classified on an ideal pyramid that represented the simplest animals on the lower levels, with complexity increasing progressively toward the top, occupied by human beings. In the Western world of the time, people believed animal species were eternal and immutable, created with a specific purpose, as this seemed the only possible explanation for the incredible variety of living beings and their surprising adaptation to their habitats.[3]
Jean-Baptiste Lamarck (1744 - 1829) was the first biologist to describe a complex theory of evolution. His theory substantially comprised two statements: first, that animal organs and behaviour can change according to the way they are used; and second, that those characteristics can transmit from one generation to the next (the example of the giraffe whose neck becomes longer while trying to reach the upper leaves of a tree is well-known). The second statement is that every living organism, humans included, tends to reach a greater level of perfection. When Charles Darwin went to the Galapagos Islands, he was well aware of Lamarck's theories and was influenced by them.
Because ethology is considered a topic of biology, ethologists have been concerned particularly with the evolution of behaviour and the understanding of behaviour in terms of the theory of natural selection. In one sense, the first modern ethologist was Charles Darwin, whose book, The Expression of the Emotions in Man and Animals, influenced many ethologists. He pursued his interest in behaviour by encouraging his protégé George Romanes, who investigated animal learning and intelligence using an anthropomorphic method, anecdotal cognitivism, that did not gain scientific support.
Other early ethologists, such as Oskar Heinroth and Julian Huxley, instead concentrated on behaviours that can be called instinctive, or natural, in that they occur in all members of a species under specified circumstances. Their beginning for studying the behaviour of a new species was to construct an ethogram (a description of the main types of natural behaviour with their frequencies of occurrence).[3] This provided an objective, cumulative base of data about behaviour, which subsequent researchers could check and supplement.
An important development, associated with the name of Konrad Lorenz though probably due more to his teacher, Oskar Heinroth, was the identification of fixed action patterns (FAPs). Lorenz popularized FAPs as instinctive responses that would occur reliably in the presence of identifiable stimuli (called sign stimuli or releasing stimuli). These FAPs could then be compared across species, and the similarities and differences between behaviour could be easily compared with the similarities and differences in morphology. An important and much quoted study of the Anatidae (ducks and geese) by Heinroth used this technique. Ethologists noted that the stimuli that released FAPs were commonly features of the appearance or behaviour of other members of the animal's own species, and they were able to prove how important forms of animal communication could be mediated by a few simple FAPs. The most sophisticated investigation of this kind was the study by Karl von Frisch of the so-called "dance language" related to bee communication.[5] Lorenz developed an interesting theory of the evolution of animal communication based on his observations of the nature of fixed action patterns and the circumstances in which animals emit them.
The Merriam-Webster dictionary defines instinct as a largely inheritable and unalterable tendency of an organism to make a complex and specific response to environmental stimuli without involving reason.[6] For ethologists, instinct means a series of predictable behaviors for fixed action patterns. Such schemes are only acted when a precise stimulating signal is present. When such signals act as communication among members of the same species, they are known as releasers. A notable example of a releaser is the beak movements in many bird species performed by the newborns, which stimulates the mother's regurgitating process to feed her offspring.[7] Another well-known case is the classic experiments by Tinbergen on the Graylag Goose. Like similar waterfowl, the goose rolls a displaced egg near its nest back to the others with its beak. The sight of the displaced egg triggers this mechanism. If the egg is taken away, the animal continues with the behaviour, pulling its head back as if an imaginary egg is still being maneuvered by the underside of its beak.[8] However, it also attempts to move other egg-shaped objects, such as a giant plaster egg, door knob, or even a volleyball back into the nest. Such objects, when they exaggerate the releasers found in natural objects, can elicit a stronger version of the behavior than the natural object, so that the goose ignores its own displaced egg in favor of the giant dummy egg. These exaggerated releasers for instincts were named supernormal stimuli by Tinbergen.[9] Tinbergen found he could produce supernormal stimuli for most instincts in animals—such as cardboard butterflies that male butterflies preferred to mate with if they had darker stripes than a real female, or dummy fish that a territorial male stickleback fish fought more violently than a real invading male if the dummy had a brighter-colored underside. Harvard psychologist Deirdre Barrett has done research pointing out how easily humans also respond to supernormal stimuli for sexual, nurturing, feeding, and social instincts.[10] However, a behaviour only made of fixed action patterns would be particularly rigid and inefficient, reducing the probability of survival and reproduction, so the learning process has great importance, as does the ability to change the individual's responses based on its experience. It can be said that the more the brain is complex and the life of the individual long, the more its behaviour is "intelligent" (in the sense of being guided by experience rather than stereotyped FAPs).
Learning occurs in many ways, one of the most elementary being habituation.[11] This process consists of ignoring persistent or useless stimuli. An example of learning by habituation is the one observed in squirrels: When one of them feels threatened, the others hear its signal and go to the nearest refuge. However, if the signal comes from an individual that has caused many false alarms, the other squirrels ignore the signal.
Another common way of learning is by association, where a stimulus is, based on the experience, linked to another one that may not have anything to do with the first one. The first studies of associative learning were made by Russian physiologist Ivan Pavlov.[12] An example of associative behaviour is observed when a common goldfish goes close to the water surface whenever a human is going to feed it, or the excitement of a dog whenever it sees a collar as a prelude for a walk.
Being able to discriminate the members of one's own species is also of fundamental importance for reproductive success. Such discrimination can be based on a number of factors. However, this important type of learning only takes place in a very limited period of time. This kind of learning is called imprinting,[13] and was a second important finding of Lorenz. Lorenz observed that the young of birds such as geese and chickens followed their mothers spontaneously from almost the first day after they were hatched, and he discovered that this response could be imitated by an arbitrary stimulus if the eggs were incubated artificially and the stimulus were presented during a critical period that continued for a few days after hatching.
Imitation is often an important type of learning. A well-documented example of imitative learning occurred in a group of macaques on Hachijojima Island, Japan. The macaques lived in the inland forest until the 1960s, when a group of researchers started giving them potatoes on the beach: soon, they started venturing onto the beach, picking the potatoes from the sand, and cleaning and eating them.[14] About one year later, an individual was observed bringing a potato to the sea, putting it into the water with one hand, and cleaning it with the other. Her behaviour was soon imitated by the individuals living in contact with her; when they gave birth, they taught this practice to their young.[15]
The National Institutes of Health reported that capuchin monkeys preferred the company of researchers who imitated them to that of researchers who did not. The monkeys not only spent more time with their imitators but also preferred to engage in a simple task with them even when provided with the option of performing the same task with a non-imitator.[16]
Individual reproduction is the most important phase in the proliferation of individuals or genes within a species: for this reason, there exist complex mating rituals, which can be very complex even if they are often regarded as fixed action patterns (FAPs). The Stickleback's complex mating ritual was studied by Niko Tinbergen and is regarded as a notable example of a FAP.
Often in social life, animals fight for the right to reproduce, as well as social supremacy. A common example of fighting for social and sexual supremacy is the so-called pecking order among poultry. Every time a group of poultry cohabitate for a certain time length, they establish a pecking order. In these groups, one chicken dominates the others and can peck without being pecked. A second chicken can peck all the others except the first, and so on. Higher level chickens are easily distinguished by their well-cured aspect, as opposed to lower level chickens. While the pecking order is establishing, frequent and violent fights can happen, but once established, it is broken only when other individuals enter the group, in which case the pecking order re-establishes from scratch.
Several animal species, including humans, tend to live in groups. Group size is a major aspect of their social environment. Social life is probably a complex and effective survival strategy. It may be regarded as a sort of symbiosis among individuals of the same species: a society is composed of a group of individuals belonging to the same species living within well-defined rules on food management, role assignments and reciprocal dependence.
When biologists interested in evolution theory first started examining social behaviour, some apparently unanswerable questions arose, such as how the birth of sterile castes, like in bees, could be explained through an evolving mechanism that emphasizes the reproductive success of as many individuals as possible, or why, amongst animals living in small groups like squirrels, an individual would risk its own life to save the rest of the group. These behaviours may be examples of altruism.[17] Of course, not all behaviours are altruistic, as indicated by the table below. For example, revengeful behaviour was at one point claimed to have been observed exclusively in Homo sapiens. However, other species have been reported to be vengeful, including reports of vengeful camels[18] and chimpanzees.[19]
| Type of behaviour | Effect on the donor | Effect on the receiver |
|---|---|---|
| Egoistic | Increases fitness | Decreases fitness |
| Cooperative | Increases fitness | Increases fitness |
| Altruistic | Decreases fitness | Increases fitness |
| Revengeful | Decreases fitness | Decreases fitness |
The existence of egoism through natural selection does not pose any question to evolution theory and is, on the contrary, fully predicted by it, as is cooperative behaviour. It is more difficult to understand the mechanism through which altruistic behaviour initially developed.
Lorenz's collaborator, Niko Tinbergen, argued that ethology always needed to include four kinds of explanation in any instance of behaviour:
These explanations are complementary rather than mutually exclusive—all instances of behaviour require an explanation at each of these four levels. For example, the function of eating is to acquire nutrients (which ultimately aids survival and reproduction), but the immediate cause of eating is hunger (causation). Hunger and eating are evolutionarily ancient and are found in many species (evolutionary history), and develop early within an organism's lifespan (development). It is easy to confuse such questions—for example, to argue that people eat because they're hungry and not to acquire nutrients—without realizing that the reason people experience hunger is because it causes them to acquire nutrients.[20]
Due to the work of Lorenz and Tinbergen, ethology developed strongly in continental Europe during the years prior to World War II.[3] After the war, Tinbergen moved to the University of Oxford, and ethology became stronger in the UK, with the additional influence of William Thorpe, Robert Hinde, and Patrick Bateson at the Sub-department of Animal Behaviour of the University of Cambridge, located in the village of Madingley.[21] In this period, too, ethology began to develop strongly in North America.
Lorenz, Tinbergen, and von Frisch were jointly awarded the Nobel Prize in Physiology or Medicine in 1973 for their work of developing ethology.[22]
Ethology is now a well-recognised scientific discipline, and has a number of journals covering developments in the subject, such as the Ethology Journal. In 1972, the International Society for Human Ethology was founded to promote exchange of knowledge and opinions concerning human behavior gained by applying ethological principles and methods and published their journal, The Human Ethology Bulletin. In 2008, in a paper published in the journal Behaviour, ethologist Peter Verbeek introduced the term "Peace Ethology" as a sub-discipline of Human Ethology that is concerned with issues of human conflict, conflict resolution, reconciliation, war, peacemaking, and peacekeeping behavior.[23]
Today, along with actual ethologists, many biologists, zoologists, primatologists, anthropologists, veterinarians, and physicians study ethology and other related fields such as animal psychology, the study of animal social groups, and animal cognition. Some research has begun to study atypical or disordered animal behavior. Most researchers in the field have some sort of advanced degree and specialty and subspecialty training in the aforementioned fields.
In 1970, the English ethologist John H. Crook published an important paper in which he distinguished comparative ethology from social ethology, and argued that much of the ethology that had existed so far was really comparative ethology—examining animals as individuals—whereas, in the future, ethologists would need to concentrate on the behaviour of social groups of animals and the social structure within them.
Also in 1970, Robert Ardrey's book The Social Contract: A Personal Inquiry into the Evolutionary Sources of Order and Disorder was published.[24] The book and study investigated animal behaviour and then compared human behaviour to it as a similar phenomenon.
E. O. Wilson's book Sociobiology: The New Synthesis appeared in 1975, and since that time, the study of behaviour has been much more concerned with social aspects. It has also been driven by the stronger, but more sophisticated, Darwinism associated with Wilson, Robert Trivers, and William Hamilton. The related development of behavioural ecology has also helped transform ethology. Furthermore, a substantial reapprochement with comparative psychology has occurred, so the modern scientific study of behaviour offers a more or less seamless spectrum of approaches: from animal cognition to more traditional comparative psychology, ethology, sociobiology, and behavioural ecology. Sociobiology has more recently developed into evolutionary psychology.
People who have made notable contributions to ethology (many are comparative psychologists):
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