Answer:
Stabilizing selection.
Step-by-step explanation:
Stabilizing selection may be defined as a type of the natural selection the mean population is stabilizes on the particular non extreme trait of a population.
The people with heterozygous condition for sickle cell trait are selected against the malaria condition. These organisms survive whereas the homozygous dominant for the normal trait and homozygous recessive dies due to malaria. Here, the heterozygous genotype individual are selected and shows the type of stabilizing natural selection.