About 7,500 years ago, in the florid forest of North Africa (now the Sahara Desert), a mosquito landed on a child’s arm and injected its needle-sharp proboscis into his skin. As the mosquito consumed that child’s blood, a deadly gang of single-celled parasites swam down the mosquito’s needle into the child’s bloodstream.

Other children had previously been bitten by the anopheles mosquito and infected by the Plasmodium parasite. Those children developed fevers, chills, headaches, nausea, vomiting and diarrhea.  Most of them died. But this particular child didn’t die. This child had developed a genetic mutation that protected against the parasite and its resulting disease: malaria.