In those parts of equatorial Africa where the malaria parasite is most common, the sickle-cell allele constitutes 20% of the ß hemoglobin alleles in the human gene pool.
In the United States, the parasite that causes malaria is not present, but African-Americans whose ancestors were from equatorial Africa are present. What should be happening to the sickle-cell allele in the United States, and what should be happening to it in equatorial Africa?
A) stabilizing selection; disruptive selection
B) disruptive selection; stabilizing selection
C) disruptive selection; directional selection
D) directional selection; disruptive selection
E) directional selection; stabilizing selection
Answer: E