Only some like it hot
As anyone who has suffered from a cold or flu knows, a high temperature is an unpleasant but important side effect of the body's immune reaction when fighting off pathogens. Laboratory studies, in which the immune responses of animals could be observed in detail, have shown that these responses display significant variations. Why doesn't every organism defend its body at the maximum possible level of intensity? New immunological theories presume that immune responses are 'costly,' that is they compete with other energy-consuming processes such as partner selection, territorial behaviour and reproduction. Each individual has limited resources and must, therefore, enter into compromises, so-called trade-offs. This could explain why different species with different living conditions also display variations in their immune responses...