Stabilizing selection is the most common form of natural selection. it eliminates any extreme expression of a trait in a population of organisms when the average expression leads to a higher rate of survival. stabilizing selection tends to a) decrease genetic sameness. b) decrease genetic diversity. c) increase the frequency of a rare allele. d) increase the frequency of two rare alleles.

B) decrease genetic diversity
Genetic Diversity refers to vast differences in genetic makeup (genotype) and thus often phenotype as well. The more that extreme genes/traits are excluded in survival and/or reproduction, leading to stabilizing selection, then the more genetically "same" or similar the population will evolve to long-term. Similarity is the opposite of diversity. Thus A) is dead wrong, B) is accurate, and both C) & D) are incorrect because "rare" means not common or "extreme." And extreme traits are exactly what decrease through stabilizing selection.
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