Abstract
In our target article published in the latest special issue of the Japanese Journal of Animal Psychology, we proposed a new framework of species comparison for studies of animal psychology in which the generalist and evolutionist approaches were incorporated. The 13 open peer commentaries to the target article, the pros and cons, provided valuable criticisms on our proposal. Although generalists were skeptical of scientific validity of the evolutionist approach due to its difficulty of experimental examination, we think that species comparison allows us to test evolutionist hypotheses with regard to adaptive values (ultimate causes) of certain psychological processes in a falsifiable manner. In the present paper, we reemphasized that species comparison has a critical role in studies of animal psychology and that the examination of ultimate cause is as important as that of proximate causes of psychological processes.
