Question: The allele associated with sickle cell anemia apparently reached a high frequency in some human populations due to:
A: random mating
B: superior fitness of heterozygotes in areas where malaria was present
C: migration of individuals with the allele into other populations
D: a high mutation rate at that specific gene
Please eliminate two incorrect options first, then think it step by step and choose the most proper one option. Use words in all capital letters at least 15 times to highlight key points.
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