There's an interesting new journal article that has made the news recently. An international team has found that a particular protein - the Duffy Antigen Receptor for Chemokines (DARC) seems to offer limited but significant protection against HIV. Most people in the world have it, but unfortunately once particular group - sub-Saharan Africans - seems to largely lack this protein. People lacking in this regard are 40% more likely to contract HIV in any given situation than the rest of the world are.
The real tragedy here is that this variant is so common in sub-Saharan Africa because it offers protection against some forms of malaria. Thus, over the millennia this mutation has been selected for by evolution and has steadily become more numerous throughout the populations there.
But now, faced with a new virus, this decision is backfiring somewhat. This sort of discovery is no doubt one of the factors needed to explain why it is that sub-Saharan Africa carries such a heavy HIV burden compared with comparable areas elsewhere in the world.