I don't understand why so many people still don't know this. It has been known for a long time.

When a person carries the gene for sickle cell anemia on one chromosome, they have the sickle cell trait, which protects against malaria. When they have it on two chromosomes, they have sickle cell anemia, a serious disease. This has resulted in an incidence of the sickle cell gene that results in the highest rate of survival, balancing the benefits and risks.

See the tab "Human Factors and Malaria" at the following link

https://www.cdc.gov/malaria/about/biology/index.html#tabs-1-3

Page last reviewed: November 14, 2018

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Two genetic factors, both associated with human red blood cells, have been shown to be epidemiologically important. Persons who have the sickle cell trait (heterozygotes for the abnormal hemoglobin gene HbS) are relatively protected against P. falciparum malaria and thus enjoy a biologic advantage. Because P. falciparum malaria has been a leading cause of death in Africa since remote times, the sickle cell trait is now more frequently found in Africa and in persons of African ancestry than in other population groups. In general, the prevalence of hemoglobin-related disorders and other blood cell dyscrasias, such as Hemoglobin C, the thalassemias and G6PD deficiency, are more prevalent in malaria endemic areas and are thought to provide protection from malarial disease.

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