The Hardy-Weinberg conditions represent an evolutionary equilibrium. If the following conditions are met, no evolution occurs:
1. Very large population
2. Isolated population
3. No mutations
4. Random mating
5. No natural selection
Condition 4, random mating, means that closely related individuals are not likely to breed, given the large population size. Therefore, expression of recessive alleles becomes less likely and the frequency of the dominant one increases.