What is the primary cause of genetic drift?

Genetic drift primarily results from random changes in allele frequencies within a population, particularly in small populations. This phenomenon occurs because, in small groups, random events can have a disproportionate effect on the overall genetic makeup of the population. For instance, if a few individuals happen to carry particular alleles and those individuals survive and reproduce, the frequency of those alleles can increase dramatically, regardless of their fitness value.

In larger populations, the impact of random events is diluted due to the greater number of individuals. As a result, genetic drift can lead to significant fluctuations in allele frequencies over generations, contributing to the divergence of populations and potentially leading to speciation events.

The other options are related concepts in evolutionary biology, but they do not directly cause genetic drift. For example, natural selection involves the differential survival and reproduction of individuals based on inherited traits, which is a non-random process. Mutation introduces new genetic variation but is not a cause of changes in allele frequencies resulting from random sampling effects seen in genetic drift. Migration can influence allele frequencies by introducing new individuals to a population, but it is not the random process characteristic of genetic drift.