A hypothesis for this observation might be that malaria is not endemic to southern Africa. It is a plausible explanation of a given scientific question.
A hypothesis is a plausible explanation of an observation of the natural world, which must be tested by using the scientific method.
Testing a hypothesis involves performing additional observational and/or experimental procedures in order to confirm or reject this assumption.
In this case, the sickle cell allele is found in high frequency in regions where malaria is endemic.
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