"When viewed from an evolutionary perspective, manifestations of infectious diseases can be classified as (1) adaptations of the host to counteract harmful aspects of the disease, (2) adaptations of the pathogen to manipulate the host, or (3) “side effects” of the disease that do not serve adaptive functions for either the host or the pathogen. Although the functions of most manifestations are not known, support or rejection of these hypotheses should be readily derivable in many cases from analyses of existing data and relatively simple experiments. This approach should lead to improved medical treatment because preferred treatment depends on assessment of the validity of the three explanations. As an illustration, this perspective and its consequences for therapy are analyzed for fever, rhinorrhea and diarrhea" (Abstract).