Which statement about natural selection over generations is most accurate?

Which statement about natural selection over generations is most accurate?

• A. Allele frequencies remain constant.
• B. All variations are equally favored.
• C. The most successful breed fixes in one generation.
• D. Over many generations, better reproducing variants increase in frequency.

Answer: (D)

Natural selection changes allele frequencies across generations as some heritable variants confer higher fitness. In each generation, individuals with traits that help them survive and reproduce leave more offspring, so the alleles for those traits become more common in the population over time. Because this effect accumulates across many generations, the variants that improve reproductive success tend to increase in frequency, shaping the population’s traits to fit the environment. That explains why the other ideas don’t fit: allele frequencies don’t stay constant when selection is acting; not all variations are equally favored, so some alleles rise while others fall; and fixing a variant in a population usually takes more than one generation, unless selection is exceptionally strong, which is not the typical outcome.

Natural selection changes allele frequencies across generations as some heritable variants confer higher fitness. In each generation, individuals with traits that help them survive and reproduce leave more offspring, so the alleles for those traits become more common in the population over time. Because this effect accumulates across many generations, the variants that improve reproductive success tend to increase in frequency, shaping the population’s traits to fit the environment.

That explains why the other ideas don’t fit: allele frequencies don’t stay constant when selection is acting; not all variations are equally favored, so some alleles rise while others fall; and fixing a variant in a population usually takes more than one generation, unless selection is exceptionally strong, which is not the typical outcome.