Variation
The reason for the increased survival of the S
gene is as follows:
Sickle-cell anemia is commonest in those parts of Africa and
the Mediterranean where the most dangerous kind of malaria occurs. Malaria is
caused by a parasite that spends part of its life in red blood cells.
AA people have little resistance
to malaraia, and many of them die of the disease. As a result, A
genes are removed from the population.
Long & Slichter