Comparative psychology usually refers to the study of the behavior and mental life of animals other than human beings. However, psychologists and scientists do not always agree on this definition. Comparative psychology has also been described as branch of psychology in which emphasis is placed on cross-species comparisons—including human-to-animal comparisons.
Some researchers however, feel that direct comparisons should not be the sole focus of comparative psychology and that intense focus on a single organism to understand its behavior is just as desirable, if not more. Donald Dewsbury reviewed the works of several psychologists and their definitions and concluded that the object of comparative psychology is to establish principles of generality focusing on both proximate and ultimate causation.
It has been suggested that the term itself be discarded since it fails to be descriptive of the field but no appropriate replacement has been found. If looking for a precise definition, one may define comparative psychology as psychology concerned with the evolution (phylogenetic history and adaptive significance) and development (ontogenetic history and mechanism) of behavior.
Using a comparative approach to behavior allows one to evaluate the target behavior from four different, complementary perspectives, developed by Niko Tinbergen. First, one may ask how pervasive the behavior is across species. Meaning, how common is the behavior in animals? Second, one may ask how the behavior contributes to the lifetime reproductive success of the individuals demonstrating it. Meaning, does it result in those animals producing more offspring than animals not showing the behavior? These two questions provide a theory for the ultimate cause of behavior.
Third, what mechanisms are involved in the behavior? Meaning, what physiological, behavioral, and environmental components are necessary and sufficient for the generation of the behavior? Fourth, a researcher may ask about the development of the behavior within an individual. Meaning, what maturational, learning, social experiences must an individual undergo in order to demonstrate a behavior? These latter two questions provide a theory for the proximate causes of behavior. For more details see Tinbergen's four questions.
The earliest works on "the social organization of ants" and "animal communication and psychology" were written by al-Jahiz, a 9th century Afro-Arab scholar who wrote many works on these subjects. The 11th century Arabic psychologist, Ibn al-Haytham (Alhazen), wrote the Treatise on the Influence of Melodies on the Souls of Animals, the early treatise dealing with the effects of music on animals. In the treatise, he demonstrates how a camel's pace could be hastened or retarded with the use of music, and shows other examples of how music can affect animal behavior, experimenting with horses, birds and reptiles. Through to the 19th century, a majority of scholars in the Western world continued to believe that music was a distinctly human phenomenon, but experiments since then have vindicated Ibn al-Haytham's view that music does indeed have an effect on animals.
Charles Darwin was central in the development of comparative psychology; it is thought that psychology should be spoken in terms of "pre-" and "post-Darwin" because his contributions were so influential. Darwin’s theory lead to several hypotheses, one being that the factors that set humans apart, such as higher mental, moral and spiritual faculties, could be accounted for by evolutionary principles. In response to the vehement opposition to Darwinism was the "anecdotal movement" led by George Romanes who set out to prove that animals possessed a "rudimentary human mind".
Near the end of the 19th century, several scientists existed whose work was also very influential. Douglas Alexander Spalding, who was called the "first experimental biologist" worked mostly with birds—studying instinct, imprinting, and visual and auditory development. Jacques Loeb emphasized the importance of objectively studying behavior, Sir John Lubbock is credited with first using mazes and puzzle devices to study learning and Lewis Henry Morgan is thought to be "the first ethologist in the sense in which we presently use the word".
Throughout the long history of comparative psychology, repeated attempts have been made to enforce a more disciplined approach, 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. 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. Indeed, some early attempts at a genuinely comparative psychology involved evaluating how well animals of different species could learn different tasks. These attempts floundered; in retrospect it can be seen that they were not sufficiently sophisticated, either in 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.
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 then 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 psychology were made by Harry F. Harlow's studies of maternal deprivation in rhesus monkeys. Interest in primate studies 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.
Since the 1990s, 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.
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, in this broad sense, include:
Many of these were active in fields other than animal psychology; this is characteristic of comparative psychologists.
Fields of psychology and other disciplines that draw upon, or overlap with, comparative psychology include:
The Donald Dewsbury book mentioned above, "Comparative Psychology in the Twentieth Century" is listed on abebooks.com