Which process actively counters genetic drift?

Gene flow is the process that counters genetic drift by introducing new genetic material into a population. When individuals from one population migrate to another and interbreed, they exchange alleles, which can either increase genetic variation or reduce the divergence between populations. This exchange helps maintain genetic diversity, which can counteract the random changes in allele frequencies that characterize genetic drift.

In smaller populations, genetic drift can lead to the loss of alleles and reduced genetic diversity, potentially compromising the population's ability to adapt to changing environments. Gene flow mitigates this by ensuring that the genetic pool remains connected, allowing for adaptability and resilience.

While mutation introduces new genetic variations into a population, it does not directly counteract the effects of genetic drift as effectively as gene flow does. Random mating also does not directly address the issues posed by genetic drift, as it refers to the mating patterns rather than gene exchange between populations. Stabilizing selection acts on existing variations by promoting average phenotypes, potentially reducing genetic diversity but not necessarily countering genetic drift directly. Thus, gene flow is the most effective answer for actively countering genetic drift.