Long-term consequence of ongoing gene flow across a species' range?

• A. Populations diverge into separate species
• B. Local adaptations become fixed in all populations
• C. Genetic drift becomes dominant
• D. Genetic differences between populations decrease, leading to greater similarity

Answer: (D)

Ongoing gene flow between populations moves alleles from one area to another, mixing their gene pools over time. This continual exchange reduces differences in allele frequencies among populations, so they become more genetically similar overall. Because migrants introduce shared variation, the population as a whole tends toward a common genetic makeup rather than diverging into distinct groups.

In contrast, divergence into separate species would require populations to become reproductively isolated, which gene flow tends to prevent. Local adaptations would be less likely to become fixed everywhere unless selection is incredibly strong across the entire range, because migrants bring alleles that may counter local favored alleles. And genetic drift, which pushes allele frequencies randomly, is strongest in small, isolated groups; gene flow actually reduces drift by boosting effective population size and introducing new alleles.