AIDS is a disease caused by the Human Immunodeficiency Virus (HIV). HIV is thought to have originated in the monkey population in Western Africa and transitioned to humans during the slaughter of a monkey with a related virus, called SIV (Simian Immunodeficiency Virus).
When an African hunter slaughtered a monkey with SIV, some of the virus entered the bloodstream of the hunter. Once inside a human host, the virus mutated to be able to infect other humans. The first human with HIV infected another human either through sexual contact, blood contact, or breastfeeding, and then continued to spread through the human population.
