Like recombination, non-random mating can act as an ancillary process for natural selection to cause evolution to occur. Any departure from random mating upsets the equilibrium distribution of genotypes in a population. This will occur whether mate selection is positive or negative assortative. A single generation of random mating will restore genetic equilibrium if no other evolutionary mechanism is operating on the population. However, this does not result in a return to the distribution of population genotypes that existed prior to the period of non-random mating. A comparison of the 2nd and 5th generations in the table below illustrates this fact.