Introduction to comparative psychology

Comparative psychology, taken in its most usual, broad sense, refers to the study of the behaviour and mental life of animals other than human beings. It is synonymous with animal psychology, but although the latter would be a more accurate term, it is less often used. Veterinarians sometimes use the phrase "animal psychology" to refer specifically to the study of disordered behaviour in animals, discussed below.

History
Comparative psychology may be said to have come into being in the late nineteenth century, with the work of George Romanes on animal psychology, inspired by Charles Darwin. It was confirmed as an important discipline within academic psychology by the experiments on instrumental learning of Edward L. Thorndike, and on classical conditioning by Ivan Pavlov. Early comparative psychology experimented on animals to discover fundamental principles, especially of learning, that might be applicable to humans. Interest in the social behaviour of animals has always also been a lesser part of comparative psychology; however the famous studies of social dominance in chickens by T. Schjelderup-Ebbe, giving rise to the concept of the "pecking order", were an important early contribution to the field.

Comparative Psychology and the Comparative Method
Strictly speaking, comparative psychology ought to involve the use of a comparative method, in which similar studies are carried out on animals of different species, and the results interpreted in terms of their different phylogenetic or ecological backgrounds. Throughout the long history of comparative psychology, repeated attempts have been made to enforce this more disciplined approach, especially since the rise of ethology in the mid twentieth century. Behavioral ecology in the 1970s gave a more solid base of knowledge against which a true comparative psychology could develop. However, the broader use of the term "comparative psychology" is enshrined in the names of learned societies and academic journals, not to mention in the minds of psychologists of other specialisms, so it is never likely to disappear completely.

A persistent question with which comparative psychologists have been faced is the relative intelligence of different species of animal. Much effort has gone into explaining that this may not be a good question, but it will not go away. Indeed, some early attempts at a genuinely comparative psychology involved evaluating how well animals of different species could learn different tasks. These attempts foundered; in retrospect it can be seen that they were not sufficiently sophisticated, either their analysis of the demands of different tasks, or in their choice of species to compare. More recent comparative work has been more successful, partly because it has drawn upon studies in ethology and behavioral ecology to make informed choices of species and tasks to compare.

Species studied
A wide variety of species have been studied by comparative psychologists. However a small number have dominated the scene. Pavlov's early work used dogs, but although they have been the subject of occasional studies since they have not figured prominently. Increasing interest in the study of abnormal animal behaviour has led to a return to the study of most kinds of domestic animal. Thorndike began his studies with cats, but American comparative psychologists quickly shifted to the more economical rat, which remained the almost invariable subject for the first half of the twentieth century and continues to be used. Skinner introduced the use of pigeons, and they continue to be important in some fields. There has always been interest in studying various species of primate; important contributions to social and developmental psycholgy were made by Harry F. Harlow's studies of maternal deprivation in rhesus monkeys. Interest in primate studes has increased with the rise in studies of animal cognition. Other animals thought to be intelligent have also been increasingly studied. Examples include various species of corvid, parrots — especially the African Gray Parrot — and dolphins.

Animal cognition
Since the 1980s, comparative psychology has undergone a reversal in its fundamental approach. Instead of seeking principles in animal behaviour in order to explain human performance, comparative psychologists started taking principles that have been uncovered in the study of human cognition and testing them in animals of other species. This approach is referred to as the study of animal cognition. It has led to significant advances in our understanding of concept formation, memory, problem solving and other cognitive abilities in animals.

Disorders of animal behaviour
Today an animal's psychological constitution is recognised by veterinary surgeons as an important part of its living conditions in domestication or captivity.

Common causes of disordered behaviour in captive or pet animals are lack of stimulation, inappropriate stimulation, or overstimulation. These conditions can lead to disorders, unpredictable and unwanted behaviour, and sometimes even physical symptoms and diseases. For example, rats that are exposed to loud music for a long period will ultimately develop unwanted behaviours that have been compared with human psychosis, like biting their owners.

The way dogs behave when understimulated is widely believed to depend on the breed as well as on the individual animal's character. For example, huskies have been known to completely ruin gardens and houses, if they are not allowed enough activity. Dogs are also prone to psychological damage if they are subjected to violence. If they are treated very badly, they may become dangerous.

The systematic study of disordered animal behaviour draws on research in comparative psychology, including the early work on conditioning and instrumental learning, but also on ethological studies of natural behaviour. However, at least in the case of familiar domestic animals, it also draws on the accumulated experience of those who have worked closely with the animals.

Noted comparative psychologists
Noted comparative psychologists, in this broad sense, include:
 * George Romanes
 * C. Lloyd Morgan
 * Edward L. Thorndike
 * Ivan Pavlov
 * John B. Watson
 * Wolfgang Köhler
 * T. Schjelderup-Ebbe
 * Clark L. Hull
 * Edward C. Tolman
 * B. F. Skinner
 * Donald Hebb
 * O. H. Mowrer
 * Neal E. Miller
 * Harry F. Harlow
 * Richard Herrnstein
 * Sara Shettleworth
 * Allen and Beatrice Gardner
 * Irene Pepperberg

It should be noted that all these were active in fields other than animal psychology, and this is characteristic of comparative psychologists.

Related fields
Fields of psychology and other disciplines that draw upon, or overlap with, comparative psychology include:
 * Animal cognition
 * Behavioral ecology
 * Conditioning
 * Ethology
 * Experimental analysis of behavior
 * Physiological psychology
 * Psychopharmacology