Why sex matters Among human and nonhuman animals, the prevalence and intensity of infection typically is higher in males than females and may reflect differences in exposure as well as susceptibility to pathogens. Elevated immunity among females is a double-edged sword in which it is beneficial against infectious diseases but is detrimental in terms of increased development of autoimmune diseases. The present book critically reviews the evolutionary origin and the functional mechanisms responsible for sexual dimorphism in response to infection. It emphasizes the value of examining responses...