as with many such genes, there’s a complexity. People who get a copy of the gene from only one parent do not develop the disease, but they do develop immunity to most forms of malaria. In other words, the gene was (and in some places still is) useful, especially in sub-Saharan Africa. Now that there are treatments for malaria, it’s less useful. But it is a reminder, when we think of messing with Mother Nature, that genes may play multiple roles and have evolutionary reasons for existing.
