Previously (Part I) the authors introduced the evolutionary biology and psychology. In the present part (Part II) of the review article, we discuss what disease is, and how diseases are explained in terms of the evolutionary perspective. Various psychologic phenomena and psychopathologic conditions are also illuminated under this evolutionary light. Through this approach, the authors hope that clinicians would search for the “normality” as well as pathology in patients, and would utilize this insight to understand and treat them accordingly.