Malaria is an ancient malady brought by mosquitoes bearing parasitic protists. The evolution of resistance is illustrated by human’s adaptive response to malaria.
Female mosquitoes pick up the microbe by feeding on the blood of an infected person. Male mosquitoes are not blood suckers, so do not transmit malaria.
2 genetic responses to malaria evolved that can themselves cause serious blood illnesses: sickle-cell anemia and thalassemia. If untreated, these mutations cause fatal red blood cell disorders in homozygotes: inheritors of the genetic mutation from both parents.
Over centuries carriers of these genetic anomalies survived while others died of malaria. This increased the frequency of the genetic variation until it became common among people living in areas where malaria was endemic.
Malaria remains prevalent in the sub-Sahara: killing 750,000 people each year, mostly young children. 40% of sub-Saharan Africans carry the sickle-cell anemia gene. 70% of Papua New Guineans inherit various thalassemia mutations.