HIV, the virus that causes AIDS, originated in non-human primates in Sub-Saharan Africa and was transferred to humans during the late 19th or early 20th century.
Two types of HIV infect humans: HIV-1 and HIV-2. HIV-1 is more virulent, is easily transmitted and is the cause of the majority of HIV infections globally. HIV-1 is closely related to a virus found in chimpanzees, and molecular phylogenetics indicates that the HIV-1 virus appeared sometime between 1884 and 1924 in equatorial Africa. HIV-2 is less transmittable and is largely confined to West Africa, along with its closest relative, a virus of the Sooty Mangabey (Cercocebus atys), an Old World monkey of Guinea-Bissau, Gabon, and Cameroon.