Abstract and subjects
HIV-1 and HIV-2 both cause AIDS in humans, and both originated in nonhuman primates in Africa before several cross-species transmission events introduced them into humans. Of more than seven such events, only one, creating the HIV-1 M group of viruses, resulted in the AIDS pandemic. Studying the evolution and epidemiology of the viruses has many uses beyond tracing their origins. Evolutionary analyses are critical for vaccine design, for identifying drug resistance mutations, for designing therapeutic drugs, and for many other purposes. This chapter provides a brief overview of the evolution of human and simian immunodeficiency viruses. Evolution is the result of a complex interplay between mutations, selection pressures in individual infected hosts, selection pressures across populations of hosts, and recombination between virus lineages.