system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Where did HIV come from?

My grandmother told me that it came from a homosexual black man in Africa "experimenting" with a monkey. The fact that she saw the need to include his race and sexual orientation leads me to question the veracity of her claim, however.
gpt
HIV does actually come from a related virus called SIV, which is common in monkeys and which can infect humans (but it doesn't do anything to humans). But the virus transmission wasn't from having sex with monkeys, it was from *eating* monkeys. "Bushmeat" is meat from wild animals in the forests of Central Africa, oftentimes monkeys. It's considered a delicacy in many African societies and an important source of protein for people too poor to raise livestock for meat. 

Anyway, SIV made the leap from monkeys to humans, where it gradually evolved into HIV, a virus that does affect humans and causes AIDS. This probably happened in the early 20th century and by the 1950s had spread all over Africa and onto other continents too. The first presumed case of AIDS in the US was a teenage prostitute in St. Louis, Missouri in the mid 1960s. He died in a hospital of a rare infection and his body showed signs of sexual abuse.