[VadeRetro]

I wonder if an analysis of the simian virus family would point to a recent intro as does the human one. The reverse of your funny coincidence is that dusky mangabys got one strain of human viruses from humans at almost the same time chimps got another strain of human virus. But what if there are equally unrelated strains in, say, gorillas that have no human counterpart? (Don't know if it's true, just wondering.)

Or are you saying that humans did get the thing from primates, only some time in the far past? Why then don't Africans show the immunity?

[CobaltBlue]

Why then don't Africans show the immunity?

Maybe they are descended from populations which were not exposed to the virus. Or maybe CCR5-delta 32 deletion confers extra susceptibility to something else in Africa.

Or maybe CCR5-delta 32 deletion immunity is associated with another virus which recombined with SIV before it became HIV.

[CobaltBlue]

Maybe chimps and dusty mangabeys both got a human virus from Europeans which recombined in both to make SIV/HIV-1 and SIV/HIV-2, respectively? Something as innocuous to us as the common cold?

This is a total WAG but I was wondering when SARS did not break out into Europeans whether there was something similar going on.