Think about it from a poker point of view

If this frequency ever varies,then evolution has occurred. Evolution is simply change in the gene pool over time. Think about it in terms of the cards. If the frequency of the cards in the deck ever changes, evolution has occurred. There are five processes that can cause the frequency to change. To remember these processes,we will use the fingers on your hands,starting from the little finger and moving to the thumb. The little finger should remind you that the population can shrink. If the population shrinks, then chance can take over.