The Red Queen's long race: human adaptation to pathogen pressure.

Pathogens, and the infectious diseases they cause, have been paramount among the threats encountered by humans in their expansions throughout the globe. Numerous studies have identified immunity and host defence genes as being among the functions most strongly targeted by selection, most likely pathogen-driven. The dissection of the form and intensity of such selective pressures have increased our knowledge of the biological relevance of the underlying immunological mechanisms in host defence. Although the identities of the specific infectious agents imposing these selective pressures remain, in most cases, elusive, the impact of several pathogens, notably malaria and cholera, has been described. However, past selection against infectious diseases may have some fitness costs upon environmental changes, potentially leading to maladaptation and immunopathology.