All biological phenomenon has both proximate cause and ultimate cause. Traditional veterinary medicine focuses proximate cause of disease. Evolutionary medicine deals ultimate cause of disease. This article introduces concepts and two themes of evolutionary medicine, infectious disease and host defense, mismatch with environment of evolutionary adaptedness（EEA). In clinical medicine of captive wild lives, mismatch with EEA is important to understand etiology of species specific diseases which captive ones are susceptible. Gastritis syndrome is a popular disease in captive cetaceans. Many factors have been suggested but specific etiology has been unknown. Captive cetaceans feed in day which humans are active, however free ranging counterparts forage day-and-night. I hypothesize that unusual situations differs from wilds may cause prolonged low pH in forestomach of captive cetaceans and make gastritis in them. My own experiences seem support some parts of the hypothesis. Evolutionary medicine may give rewarding insights into wildlife medicine, but critical attitudes and alternative hypothesis should be kept in mind to prevent its easy application.