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Ethology (from Greek: ήθος, ethos, "custom"; and λόγος, logos, "knowledge") is the scientific study of animal behavior, and a branch of zoology.
Although many naturalists have studied aspects of animal behavior through the centuries, the modern science of ethology is usually considered to have arisen as a discrete discipline with the work in the 1920s of biologists Nikolaas Tinbergen of The Netherlands and Konrad Lorenz of Austria. Ethology is a combination of laboratory and field science, with strong ties to certain other disciplines — e.g., neuroanatomy, ecology, evolution. The ethologist, a scientist who practices ethology, is interested in the behavioral process rather than in a particular animal group and often studies one type of behavior (e.g., aggression) in a number of unrelated animals.
The desire to understand the animal world has made ethology a rapidly growing field, and since the turn of the 21st century, many prior understandings related to diverse fields such as animal communication, personal symbolic name use, animal emotions, animal culture and learning, and even sexual conduct, long thought to be well understood, have been revolutionized, as have new fields such as neuroethology.

Etymology
Comparative psychology also studies animal behaviour, but, as opposed to ethology, construes its study as a branch of psychology rather than as one of biology. Thus, where comparative psychology sees the study of animal behaviour in the context of what is known about human psychology, ethology sees the study of 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 look at 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 lead to different perspectives and sometimes to 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, and this led to different emphases as well as somewhat differing philosophical underpinnings in the two disciplines. A practical difference is that early comparative psychologists concentrated on gaining extensive knowledge of the behaviour of very few species, while ethologists were more interested in gaining knowledge of behaviour in a wide range of species in order to be able to make principled comparisons across taxonomic groups. Ethologists have made much more use of a truly comparative method than comparative psychologists ever have. Despite the historical divergence, most ethologists (as opposed to behavioural ecologists), 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 rule the evolution of the living species: there is therefore a strong connection between these two fields.

Before Darwin: Scala Naturae and Lamarck's theories
Because ethology is understood as a branch of biology, ethologists have been particularly concerned 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, has 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 first step in 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). This approach provided an objective, cumulative base of data about behaviour, which subsequent researchers could check and build on.

Darwinism and the beginnings of ethology
An important step, 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. The ethologists noted that the stimuli that released FAPs were commonly features of the appearance or behaviour of other members of their own species, and they were able to show 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" underlying bee communication. 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 fixed action pattern and animal communication
Modern psychoanalysis defines instinct as an impulse which forces an individual to accomplish a task through pre-defined mental schemes, behaviours that are not caused by the usual learning process nor personal choice. In ethology, by instinct we mean a series of rigid and predictable actions and behavioural schemes which go under the term of 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 go under the name of releasers. Notable examples of releasers are, in many bird species, the beak movements by the newborns, which stimulates the mother's regurgitating process to feed the child. Another well known case is the classic experiments by Tinbergen and Lorenz on the Graylag Goose. Like similar waterfowl, it will roll 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 behavior, pulling its head back as if an imaginary egg is still being maneuvered by the underside of its beak. However, it will also attempt to move other egg shaped objects, such as a golf ball, door knob, or even an egg too large to have possibly been laid by the goose itself (a supernormal stimulus). As made obvious by this last example, however, a behaviour only made of fixed action patterns would result particularly rigid and inefficient, reducing the probabilities of survival and reproduction. The learning process has therefore a great importance, as the ability to change the individual's responses change 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 will result "intelligent" (in the sense of guided by experience rather than rigid FAPs).

Instinct
The learning process may take place in many ways, one of the most elementary is assuefaction. This process consists in ignoring a persistent or useless stimuli. An example of learning by assuefaction is the one observed in squirrels: when one of them feels in danger, the others hear its signal and go to the nearest repair. However, if the signal comes from an individual who has performed a big number of false alarms, his signal will be ignored. Another common way of learning is by association, where a stimuli is, based on the experience, linked to another one which may not have anything to do with the first one. The first studies of associative learning were made by Russian physiologist Ivan Pavlov. 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. The associative learning process is linked to the necessity of developing discriminatory capacities, that is, the faculty of making meaningful choices. Being able to discriminate the members of your own species is of fundamental importance for the reproductive success. Such discrimination can be based on a number of factors: in many species (among which birds), however, this important type of learning only takes place in a very limited period of time. This kind of learning is called imprinting.

The learning process

Main article: Imprinting (psychology) Imprinting
Finally, imitation is often a big part of the learning process. A well-documented example of imitative learning is that of macaques in Hachijojima island, Japan. These primates used to live in the inland forest until the 60s, when a group of researchers started giving them some potatoes on the beach: soon they started venturing onto the beach, picking the potatoes from the sand, and cleaning and eating them. 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 children.

Imitation
The individual reproduction is with no doubt the most important phase in the proliferation of the species: for this reason, we can often observe complex mating ritual, which can reach a high level of complexity even if they are often regarded as FAPs. Sticklebacks complex mating ritual was studied by Niko Tinbergen and is regarded as a notable example of fixed action pattern. Often in social life, males are fighting for the right of reproducing themselves as well as social supremacy. Such behaviours are common among mammals. A common example of fight for social and sexual supremacy is the so-called pecking order among poultry. A pecking order is established every time a group of poultry co-lives for a certain amount of time. In each of these groups, a chicken is dominating among the others and can peck before anyone else without being pecked. A second chicken can peck all the others but the first, and so on. The chicken in the higher levels can be easily distinguished for their well-cured aspect, as opposed to the ones in the lower levels. During the period in which the pecking order is establishing, frequent and violent fights can happen, but once it is established it is only broken when other individuals are entering the group, in which case the pecking order has to be established from scratch.

Mating and the fight for supremacy
Social life is probably the most 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 in a well-defined rule on food management, role assignments and reciprocal dependence. The situation is, actually much more complex than it looks. When biologists interested in evolution theory first started examining the social behaviour, some apparently unanswerable questions came up. How could, for instance, the birth of sterile casts, like in bees, be explained through an evolving mechanism which emphasizes the reproductive success of as many individuals as possible? Why, among animals living in small groups like squirrels, would an individual risk its own life to save the rest of the group? These behaviours are examples of altruism. Of course, not all behaviours are altruistic, as shown in the table below. Notably, revengeful behaviour is claimed to have been observed exclusively in Homo sapiens.
The existence of egoism through natural selection doesn't pose any question to the evolution theory and is, on the contrary, fully justified by it, as well as for the cooperative behaviour. It is much harder to understand the mechanism through which the altruistic behaviour initially developed.

Society life
Insect societies are among the most ancient and complex. As well as for many other species, it is believed that social insects evolved from solitary ones. Many species of bees and vespidae alive today are solitary and many others have different grades of sociability; it is therefore possible to build a complete picture of the various stages of evolution just by analysing today's living species, much like astronomers study in the sky a picture of the universe in the various stages of its life, depending on the distance of the observed object.
In solitary species, the female builds a nest, deposits her eggs and food reserves in it and then abandons it forever. The mother dies shortly after. In the so-called presocial (or subsocial) species, the mother comes back to feed the larvae for a certain amount of time, and the next generation then deposit their eggs in the same nest. However, the colony is not permanent (it will often be destroyed by winter), there are no assigned roles and all females are fertile. Eusocial (from Greek, very social) insects cooperate completely in caring for larvae and each individual has a clear task to complete in life; among these there are sterile individuals working to the advantage of fertile ones. Most species of ants and termites are classified as eusocial, as well as many common species of bees and vespidae.
A colony of eusocial bees typically includes 30,000 to 40,000 individuals and an adult queen. Every working bee is born from an egg laid by the queen. The egg hatches into a larva, which is continuously fed by dedicated bees. When the larva fills the whole cell, the cell is sealed with wax. After two weeks, during which the larva transforms into an adult bee, the individual leaves the cell and rests for a day or two.
After this short resting period, the bee will have to accomplish a series of tasks. The first is to feed larvae, the queen and the males. This period lasts about one week, but duration varies depending on the needs of the colony. The bee then starts producing wax, used to enlarge the honeycomb. During this stage, the bee can also dispose of dead or ill bees, clean cells and make short excursions to familiarize itself with the local surroundings. It is only in the last part of its life that the bee will go in search of nectar, and the bee will be dead by the sixth week. Queens are grown in larger cells than usual. Although all the eggs have the genetic potential to become queen, they only develop under very precise conditions. According to recent studies, such bees would become queens thanks to a more substantial alimentation -- rich with proteins -- already in the larval state, in contrast with the alimentation mainly based on carbohydrates (honey) which normal bees are fed. The queen bee keeps the control of her servants be releasing specific chemical substances which inhibit the sexual maturation of the normal bees. If the queen is lost, the bees notice immediately and start building larger cells to host the larva of a new queen.
One of the main differences between subsocial and eusocial bees is that the second survive during the winter: they keep the hive temperature constant by getting close to each other.
During the spring, when the big quantity of nectar makes it possible, the hive splits in two separate colonies, where the queen guides her half hive to a new location. The new queen, which is grown as soon as the original queen leaves, mates. The reproduction is the only contribute by the male to the social life of the hive, which, not being able to feed autonomously, are eventually killed in autumn, when food reserves start getting smaller.

An example of social life: bees

Main article: Tinbergen's four questions Tinbergen's four questions for ethologists
Through the work of Lorenz and Tinbergen, ethology developed strongly in continental Europe in the years before World War II. 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. In this period, too, ethology began to develop strongly in North America.
Lorenz, Tinbergen, and von Frisch were jointly awarded the Nobel Prize in 1973 for their work in developing ethology.
Ethology is now a well recognised scientific discipline, and has a number of journals covering developments in the subject, such as the Ethology journal.

The flowering of ethology
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--looking at 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.
Indeed, 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 and Richard Dawkins. The related development of behavioural ecology has also helped transform ethology. Furthermore, a substantial rapprochement 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.

Social ethology and recent developments

There are often mismatches between human senses and those of the organisms they are observing. To compensate, ethologists often reach all the way back to epistemology to give them the tools to predict and avoid misinterpretation of data.
"Super-real object" is an object that causes an abnormally strong response in an animal. An example of this is the design of dummies that mimic and over-stress the key characteristics of individuals in certain species causing animals to direct behaviour to the super-real object and ignore the real object. A super-real object may cause pathologies and we can see many examples in humans (super-sweet food, super-big female traits, super-relaxing drugs, etc.). See the book, Foundations of Ethology by Konrad Lorenz.
Deleuze draws upon the notions of ethology in his book "Spinoza: Practical Philosophy" to develop his ontology, most specifically in reference to the plane of immanence. List of ethologists

Altruism in animals
Animal cognition
Animal communication
Anthrozoology
Behavioral Ecology
Cognitive ethology
Emotion in animals
Important publications in ethology
Non-human animal sexuality
Phylogenetic comparative methods
Sociophysiology