Final answer:
A circumstance that violates the Hardy-Weinberg equilibrium includes genetic drift, natural selection, non-random mating, gene flow, and mutation. Natural selection and gene flow, among others, can alter allele frequencies and disrupt equilibrium.
Step-by-step explanation:
Under the Hardy-Weinberg model of population dynamics, a circumstance that violates the conditions of Hardy-Weinberg equilibrium includes genetic drift, natural selection, non-random mating, gene flow (migration), and mutation. These factors can cause changes in allele frequencies within a population, which means the population would not be in equilibrium.
To succinctly address the student's question, among the options provided, natural selection and gene flow are directly stated as disturbances to Hardy-Weinberg equilibrium. Random mating is actually a condition required to maintain equilibrium, not a violation. However, it's worth noting that mutation, while not given in the provided choices, is also a violation.
A population that has violated the conditions of Hardy-Weinberg Equilibrium could be a population with changing allele frequencies over time due to the evolutionary forces mentioned. An infinitely large population and one in which allele frequencies do not change over time are both in line with the Hardy-Weinberg conditions, assuming the other conditions are also met.