The Hardy-Weinberg equation is dead simple, but has profound implications. It follows from basic statistics and probability that random mating in a substantial population, when there is no migration and no selective pressures, will maintain the frequency of each allele for each gene within the population. In other words, if 30% of the population shows a particular trait, then in successive generations, 30% should continue to show that trait. If the conditions above are met.
The beauty lies in that allele frequencies do change over time. And they can only do so if something is affecting them. If mating is not random, or if there are selective pressures, or migration, or a small population size, a shift in allele frequencies will occur.
By investigating why the Hardy-weinberg equilibrium doesn’t hold for a poultaion, we can determine what the cause of frequency change is, and learn more about the nature of living things on this planet.
And I think that is way cool.