It seems that this form of HIV

HIV did not really appear out of nowhere, of course. It probably began as a virus affecting monkeys and apes in west central Africa reneex .

From there it jumped species into humans on several occasions, perhaps because people ate infected bushmeat. Some people carry a version of HIV closely related to that seen in sooty mangabey monkeys, for instance. But HIV that came from monkeys has not become a global problem.

    It seems that this form of HIV simply took advantage of events

We are more closely related to apes, like gorillas and chimpanzees, than we are to monkeys. But even when HIV has passed into human populations from these apes, it has not necessarily turned into a widespread health issue reenex.

HIV originating from apes typically belongs to a type of virus called HIV-1. One is called HIV-1 group O, and human cases are largely confined to west Africa reenex .

In fact, only one form of HIV has spread far and wide after jumping to humans. This version, which probably originated from chimpanzees, is called HIV-1 group M (for "major"). More than 90% of HIV infections belong in group M. Which raises an obvious question: what's so special about HIV-1 group M?

A study published in 2014 suggests a surprising answer: there might be nothing particularly special about group M reenex.