The population in South Africa is more prone to sickle cell anemia (genotype “ss”). People with genotype “ss” survive only up to
14-15 years of age. People with “SS” are prone to malaria because the parasite resides inside their RBCs. People with genotype "Ss" are resistant to malaria because the parasite cannot reside inside their RBCs, and they can live a normal life (without sickle cell anemia). What kind of evolutionary force must be operative in South Africa?
Indeed, there are several alleles, providing protection against malaria, including allele of sickle-cell anemia (hemoglobin S), alpha- and beta-thalassemia, hemoglobin C and hemoglobin E. There are visible signs of strong selection pressure. First, abundance alleles suggests that the selection of supports almost any shape adaptation to the disease. Secondly, the pressure is so strong that despite the fact that almost all of these adaptations is very costly to their media, they are still maintained by selection.
