The Hardy-Weinberg principle states that the genetic variation in a population stays constant over generations in the absence of disruptive factors. The concept predicts that when mating occurs randomly in a vast population, the allele and genotype frequencies remain consistent because they are in equilibrium.
The Hardy-Weinberg equilibrium can be subverted by a variety of external factors, including natural selection, mating practices, gene flow, mutations and genetic drift. For example, mutations undermine the equilibrium of allele frequencies through presenting new alleles into a population. Natural selection subverts the Hardy-Weinberg equilibrium model because it changes the gene frequencies. The Hardy-Weinberg principle rarely exists in reality because disruptive factors are commonly found in nature.