In the context of evolution by natural selection, does natural selection act directly on an organism's genotype or phenotype?

• A. Both genotype and phenotype equally and independently, because selection targets DNA and traits as separate units of evolution.
• B. Genotype, because selection directly changes allele frequencies by targeting specific DNA sequences regardless of their expressed traits.
• C. Neither genotype nor phenotype, because genetic drift is the only mechanism that changes allele frequencies over time.
• D. Phenotype, because selection favors individuals with traits that affect survival and reproduction in a given environment.

Answer: (D)