After some scientists from the University of Montpellier (France) monkeyed around with HIV genetics, they traced HIV-1 groups O and P (which are highly lethal) to Gorillas in Cameroon. These findings show that the evolutionary history of HIV is a complicated one. Thanks to genetic samples from the stool of gorillas and chimpanzees from Cameroon, Gabon, Uganda, and DRC, the team made this discovery.
The virus isn't especially common in gorilla populations, but it was just common enough for it to jump to humans and wreak havoc. It turns out that the nature of the HIV O and P cytidine deaminase stopped transmission between chimpanzees and gorillas, but not between gorillas and humans.
The UN estimates that 78 million people have died from HIV since 1981. Even though we have good antivirals, not everyone has access to them.
I know what you're thinking...
This photo is relevant because meat.... as with other strains of HIV, the first people became infected from eating bush meat.