How can the hardy-weinberg equation be used to model selection?
The Hardy-Weinberg principle is used when describing a population of organisms in which the organisms do not change.
This principle explains the requirements of a population in order to remain constant (no mutations or evolution) for generations. So basically, there would be no natural selection. All the organisms would be equally adapted to their environment and distribute genes throughout a population.
The Hardy-Weinberg principle includes factors such as movement in and out of a population, mate choice, mutation, selection, genetic drift, and meiotic flow when describing a population which does not change. All of these previous factors must remain constant i.e. no movement in and out of a population, because this would bring new genes into the pool.