Simian immunodeficiency viruses (
SIVs) are
retroviruses able to infect at least 45 species of African non-human
primates. Based on analysis of strains found in four species of
monkeys from
Bioko Island, which was isolated from the mainland by
rising sea levels about 11,000 years ago, it has been concluded that SIV has been present in monkeys and apes for at least 32,000 years, and probably much longer.