How did the HbS mutation evolve and why it persists today among certain populations?
Based on experimental evidence of a reduced incidence of malaria among people carrying sickle cells in their blood stream, it is now assumed that the presence of the sickle cell trait protects individuals against malaria. Malaria parasites that invade red blood cells of individuals carrying the trait die with the cells when the latter assume the sickle shape and adhere to the walls of the blood vessels. The hemoglobin S (HbS) mutation that protects against malaria did not develop as a response to malaria itself. It occurred by chance. Those people without the mutation, living in areas where malaria epidemics were common, were at an increased risk to contract this infectious disease, getting symptoms of high fevers, headache, muscle pain, enlarged spleen, and anemia. People carrying only two HbA (non-sickle cell) genes often died in their first few year of life. Those who were lucky enough to carry the HbS gene when malaria struck, had a better chance of living. They would survive to pr