The other posts addressed how Simian Immunodeficiency Virus (SIV) mutated into Human Immunodeficiency Virus (HIV) but where did SIV come from? The ancestor to SIV is the Feline Immunodeficiency Virus (FIV) sometimes known as "Cat AIDs". My cat has FIV so it is something that I've studied. FIV has almost the same DNA sequence as HIV. The ancestory of FIV to HIV is beyond doubt. An FIV virus can actually inject its DNA into a human cell. Fortunately in the case of humans, nothing happens. The DNA for FIV simply does not work inside a human cell. Cats like to bite and claw one another when defending their territory so it's no surprise that FIV has spread far and wide in certain populations (supposably it is pandemic in Australia). Somewhere I read that most wild lions have FIV. Cats have been living with FIV for so long that they have developed some immunity to it. My cat is almost 17 years old. Unfortunately due to the FIV, bacterial infection has damaged the valves in his heart. I've now got him on heart medication to deal with that. He's a sweet cat and an old friend but expensive to keep alive.

Gary