Six realms of existence are identified in Buddhism: gods, demigods, humans, animals, hungry ghosts, and hells. They are each the result of one of the six main negative emotions: pride, jealousy, desire, ignorance, greed, and anger.
Looking at the world around us, and into our own minds, we can see that the six realms definitely do exist. They exist in the way we unconsciously allow our negative emotions to project and crystallize entire realms around us, and to define the style, form, flavor, and context of our life in those realms. And they exist also inwardly as the different seeds and tendencies of the various negative emotions within our psychophysical system, always ready to germinate and grow, depending on what influences them and how we choose to live.