Comparative psychology refers to the scientific study of the behavior and mental processes of non-human animals, especially as these relate to the phylogenetic history, adaptive significance, and development of behavior. Research in this area addresses many different issues, uses many different methods and explores the behavior of many different species from insects to primates.
Comparative psychology is sometimes assumed to emphasize cross-species comparisons, including those between humans and animals. However, some researchers 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 so. 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.
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 (i.e. how common is the behavior between animal species?). Second, one may ask how the behavior contributes to the lifetime reproductive success of the individuals demonstrating the behavior (i.e. does the behavior result in animals producing more offspring than animals not displaying the behavior)? Theories addressing the ultimate causes of behavior are based on the answers to these two questions.
Third, what mechanisms are involved in the behavior (i.e. 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 (i.e. what maturational, learning, social experiences must an individual undergo in order to demonstrate a behavior)? Theories addressing the proximate causes of behavior are based on answers to these two questions. 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 writer Ibn al-Haytham (Alhazen) wrote the Treatise on the Influence of Melodies on the Souls of Animals, an 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.