Hardy-Weinberg equilibrium in a concept that states that a population's genotype frequencies stay the same over time as long as certain conditions are met. There are five conditions needed for a population to stay in equilibrium. Populations that meet these conditions are not evolving. The conditions are that the population must be very large, so no genetic drift can occur; no emigration or immigration, so no gene flow can occur; no mutations can occur; mating must random, so no sexual selection can occur; and there must be no natural selection, with all traits equally aiding survival. However, all these conditions are rarely met by real populations.