Which genomic pattern would support rapid adaptation via standing variation?

• A. Unique new mutations in each population.
• B. Lack of any allele frequency changes.
• C. Elevated diversity around selected loci with no allele frequency change.
• D. Repeated gains of the same allele across populations without new mutations, or shared ancestral alleles at the same loci.

Answer: (D)

Rapid adaptation via standing variation occurs when beneficial alleles already exist in a population before the environmental change, so selection can quickly raise their frequencies. The pattern that fits this best is finding the same advantageous allele across multiple populations, either because it came from a shared ancestral pool or because selection repeatedly acts on the same standing allele in different populations. This lets adaptation happen rapidly without waiting for new mutations. In contrast, unique new mutations in each population would slow adaptation, no allele frequency change means there’s no adaptive shift, and elevated diversity around a locus without a frequency change wouldn’t reflect selection driving adaptation.