Final answer:
The Hardy-Weinberg principle explains how genetic variation in natural populations is maintained. It states that allele and genotype frequencies will remain stable over time under certain conditions.
Step-by-step explanation:
The balance hypothesis of how much genetic variation exists in natural populations is described by the Hardy-Weinberg principle. This principle states that a population's allele and genotype frequencies will remain stable over time under certain conditions. These conditions include no mutations, no gene flow, random mating, no genetic drift, and no selection. If the frequencies of alleles or genotypes deviate from the values expected from the Hardy-Weinberg equation, then the population is evolving.