Author Edward Hooper is probably most famous for his book titled The River. In it he attempts to trace the history of HIV and how humans contracted it. His theory is that infected lots of an experimental polio vaccine were to blame for the cross over of SIV (the simian version of HIV). Human intervention played the key role in starting the disease. However, most of the lots have been tested for SIV and none have been found that contain the virus (BBC Polio link)
Now a virologist, Preston Marx, has a new theory. Once again, human intervention plays the key role. He wanted to test the idea that monkey bites were responsible for the introduction of humans to HIV. But the data that he collected did not seem to support this.
So instead he started to think much like Hooper did. He investigated the effect humans might have had, and in particular the vaccination campaigns. However, this is where Marx and Hooper go their separate ways. Marx thinks that unclean needles in other vaccination campaigns are to blame (the polio vaccine was attenuated, so it was fed to people, not injected).
The theory starts out with a hunter becoming infected with SIV (through either bites, or eating uncooked meat). Usually the immune system would be able to beat the infection, but if a slightly mutated virus were to jump to another host then it would have more time to mutate into something deadly to humans. The unsterilized needles would allow the virus to transfer among a large population in a short time period, also allowing it more time to mutate.
That man might have caused HIV is a sobering thought. The good intentions of a few could have inadvertently caused one of the greatest problems to plague humans in the 20th century. It is a reminder that any action can lead to devastating consequences.