In regions where HIV has been around for a long time the disease seems to have mutated into a less lethal form.
The virus gets into a person who has an especially efficient immune system, and either the virus gets wiped out or it adapts. The adaptation changes it into a milder form. Then if the person spreads it to someone else, the recipient gets the milder version. That's the theory explained in HIV evolving 'into milder form'. Excerpt:
The team showed this process happening in Africa by comparing Botswana, which has had an HIV problem for a long time, and South Africa where HIV arrived a decade later.
Prof Goulder told the BBC News website: "It is quite striking. You can see the ability to replicate is 10% lower in Botswana than South Africa and that's quite exciting.
"We are observing evolution happening in front of us and it is surprising how quickly the process is happening.
"The virus is slowing down in its ability to cause disease and that will help contribute to elimination."
Fascinating, if true.
If no efforts had been made to slow the disease then presumably those humans with built in immunity would survive, their offspring would also carry that immunity, and in the evolutionary process the world would eventually be inhabited with people with that immunity. But here we are told that the virus itself is adapting and evolving. It's a constant war between humans and the things that want to kill them.