That could be for all I know. At least, I've heard the theory. Can't remember exactly how that's supposed to have worked, though. Does it mean the humans had the HIV first? From where? Why didn't we notice before the late 70s?
Because dying of diarrhea and emaciation wasn't so remarkable in the past? Because it is a very slow disease to progress and people didn't use to live as long as they do now? Because globalization has spread it further and faster than ever before? Because in the past homosexuals didn't go flying all around the world, looking for action? Because in the past truck drivers didn't drive all over Africa sleeping with women and spreading the disease through every village? Because in the past, there were no needles for spreading diseases intravenously? Because, once we had good sanitation to prevent most diseases and cures for most of the diseases that were left, this one stuck out like a sore thumb? For that matter, what happened to SARS? Where did it come from? Where did it go?