Step-by-step explanation:
The allele for sickle cell would gradually be eliminated from the populations over generations. This is because while initially natural selection favoured and fitted the allele in the environment because its bearers are less vulnerable to malaria, sickle cells also result in reduced capacity of the red blood cells to carry oxygen to tissues. Therefore in the absence of Malaria, sickle cell would thereby offer a disadvantage to an individual hence be eliminated by natural selection.