The Huayan Sutra tells us that evil deeds cause rebirth in one of the Six Realms. There are, I believe Three Realms of Buddhists who have an opinion on this matter of Life & Death (and Rebirth). The first are those who fervently believe in the very strict interpretation of Rebirth, Karma, how they relate to one another, and that achieving the state of Nirvana equates with no further rebirth. The second group are the ones who disavow even the remote possibility of there being such a thing as rebirth; karma is out also, especially the part about karma spanning across lifetimes. The third are those who maintain a more open view of rebirth—not quite agnostic about it, maybe fitting cellular rebirth (every seven years, there's a whole new you! Except some of the new you is 6 years and 364 days old.).
Most of the Zen practitioners I know personally tend to be in the camp of, “We can be, and in fact are, reborn every second.” That would include me. It's not something I can prove or disprove, not something I'm even particularly inclined to spend much time on, especially to be argumentative: “Of course there's rebirth!” “Oh yeah, says you!” (I must qualify that most discussions about rebirth I've encountered don't really sound quite that much like a script from a 1930's gangster movie, but they would be so much more entertaining if they were). I'm more inclined to pay attention to what I'm doing in the here&now, not so much on what got me here in the ancient twisted karma/rebirth sense, more in the “What I've done every second of my life has created my current situation, and the collective actions of everyone who has ever lived has gotten us all collectively to the point where we all are, right here&now in this very second” sense.
From the classical Buddhist version, there are the Six States of Existence, the Six Realms into which we as the current crop of humans can be reborn into:
Devas—godlike creatures who despite their lofty status aren't exempt from sickness, old age and death.
Asuras—sometimes called “titans” or “demons,” but not in the Western “Satan” sense of demon.
Humans—If nothing else, this is the plane of existence from which we can become enlightened. So in spite of the Three Dharma Seals of dukkha, anicca, and anatman—struggle, impermanence, and no self—it seems like a reasonable trade-off. I should add here that given that I have no reason to believe that I just sprung out as the first one of anything, so I'm here as a result of rebirth. The Sutra of Perfect Enlightenment has a good take on that.
Animals—Not animals in a snarly dog-eat-dog way necessarily, more of the “it's a dog's life” way of not really having any responsibilities, a pretty basic, if limited, life.
Hungry Ghosts—They of the insatiable appetite, with massive distended bellies, needle-thin throats, and mouths either the size of a needle, or huge enough to match the belly.
Hell-beings—As unpleasant as you'd think from the name, but not really a “burn in hell for all eternity” unpleasantness that Western culture, myths, and legends have given us.
One of the reasons that I don't have any problem with these realms being states of rebirth is that I know beings who fit into those categories. I think most of us across the span from (re)birth-to-death probably fit into one or more of them easily, most likely all of them at one point or another. And as a matter of course, I have my own “here&now” interpretations of them, which will hopefully offend none of the Three Realms of Buddhists mentioned above. Rebirth doesn't necessarily imply a physical death is required.
Devas are the ones with First-World problems. They might even fit into the 1 percenters, but I suspect that any of us who don't have to worry about being bombed, shot, starved, homeless, or or generally “devastated,” might fit into the Deva realm on a lot of days. If we aren't there, we'd like to be. The issue with the Devas is that they have it so easy that it's totally unimaginable that others could have it worse than they do. There's no real wisdom in Deva-land, and certainly no compassion of empathy. No Bodhisattvas to be found. Succinctly, I refer to it as the “Let them eat cake” realm.
Asuras are the ones that try to appear to be above the fray. The kind of self-righteous, self-involved, self-important type who will talk your ear off about themselves, but would look at their watch and tap their foot impatiently if someone else has the audacity to waste the Asuras time by talking about themselves. Asuras will look down on others, they're prone to making themselves look good, either by inflating stories about themselves, or by pulling someone else down. Either way that the Asura accomplishes it, his or her self-serving nature is just a way to create a permanent sense of “Self.” A lot of “I,I,I,I” here, no “How may I help you.” It could be called the “They should pull themselves up by their bootstraps, the lazy bastards” realm.
Humans, as I mentioned previously, have the ability to become awakened, right here in this space in between (re)birth and death. Depending on your interpretation, if you attain Nirvana, “Ain't coming back, see ya.” Maybe reaching our Awakened nature means rebirth as a Bodhisattva, being reborn as many times as it takes for all sentient beings to attain awakening. And depending on how scripturally- inclined you are, you might even be able to pick the form of rebirth. Human isn't a bad rebirth as rebirths go, lots of potential, but no guarantees. There are probably some who take rebirth as a human as a cosmic consolation prize; “Better luck next time, pal.” And the there are probably those who, upon acknowledging their rebirth as a human say, “Ugh. This again?” Some days (or instants) it's great. Other days (or years), not so much. Sounds like The Three Dharma Seals to me. Overall, the pendulum swings, but never that far from the Middle Path, even though we may have our moments of, “It's the end of the world,” alternating with, “This is the greatest thing that has ever happened,” which will of course be replaced by “the end of the world” in an instant. Those extremes aren't real though; it's never as bad or as good as we think it is.
Animals, well, I'll get around to writing about animals, I need a nap now. The animal realm is full of the cat who is lolling in the sunbeam on the floor, then when the sunbeam moves, the cat's even too lazy to follow it. “Sloth” is about as good a word as there is for covering the meanings of “Animal.” Predictability is really important, because if it's predictable, there's no need to fear. There aren't a lot of demands, but the ones there are—like food being in our bowl, or being able to control the entire world with our hand firmly attached to the steering wheel of existence. Just not if that entails too much effort. Now can you get up and change the channel on the TV?
It's tough to detach from that Western hell-fire & brimstone image of the pit of flames for all eternity. Being as that it's a realm of rebirth, that literally means that it is as impermanent as anything else, so once you enter the gates of hell, you don't have to stay there forever. Even that is no consolation though. If where we are is unpleasant, we will let everyone within earshot know all about it, and probably at top volume. Disagree? “Choose your weapon, sir. We're going to settle this once and for all!” But it's never settled, let alone “for all.” There will be the next issue to complain about. And complain is way too polite for the Hell-Being. Attack, rip your head off, throw in “How dare you” for good measure, and then we're approach the outskirts of Hellbeingville. The level of attack goes well beyond, “If mama ain't happy, ain't nobody happy.” Think of the crankiest kid you've ever come across, then hand him an AK-47. Now we're getting there. There are a few Zen stories about the Hell-Being realm. My favorite is that of Wonhyo, the “Buddhist Saint of Korea,” who was once a pious scholar, and then roamed among the prostitutes, drunkards, thieves, and all other “lowly” (re)born, because “Even Hell-Beings need saving.” The Hell Being isn't going to do any saving, so somebody had to go into the market place with outstretched arms, and Wonhyo was just the guy to do it.
Hungry Ghosts are probably the realm with the most interesting back story. They're to whom Nancy Reagan in her infinite wisdom directed, “Just say no”, and in her infinite stupidity didn't seem to realize that a Hungry Ghost is incapable of just saying “No.” Dr. Gabor Maté worked among the addict population in Vancouver, BC, and he wrote a book called, “In the Realm of Hungry Ghosts.” It's a really good crossover between some Buddhist elements and some medical. It's not just the drug addict who is the Hungry Ghost though. Anyone who has ever obsessed excessively about something, be it food, sex, alcohol, drugs, fame, fortune, money, or just wants more because what they have is never enough, could qualify at a Hungry Ghosts Anonymous meeting. That's why I like the massive mouth and the bloated belly image. That little tiny throat just doesn't allow for the appetite to be sated, no matter how much you try to stuff into the massive hole. It's just not going to reach the other massive hole. If there's some, that calls for more. And where the “more” comes from might be from you, and the means of obtaining “more” are completely inconsequential. Anything from murder to character assassination are on the table, so long as it provides “more.” Problem is, “more” is just never enough. That pendulum is swinging pretty wide with the Hungry Ghost, and usually only in one direction. Do you have maybe a little more than your share of Greed, Anger, and Delusion? Maybe a lot more? “Welcome to the Wonderful World of the Hungry Ghost!” Bodhisattvas need not apply.
If we go to the moment-to-moment approach to rebirth, I think that one time or another, we've been reborn many times in all these realms...and without bothering to die in between them. At least it's not in the literal sense of dying. But in a way, something does die before each of those realms rolls our way. Generally, we could say that we're “killing” the innate Buddha, choosing a course of thought, speech and action that is anything but Buddha-like. Maybe we forsake View for view. Maybe Wisdom is too damn hard, concentration and paying attention are at best inconvenient. And you have to put food on the table, so we can convince ourselves that how it gets there is unimportant, just so long as the dough is rolling in.
Maybe we can't always see our hungry, ghostly selves when we're in that realm. But maybe we can see when that or any of the other realms is looming; that they will detract from our very humanity. If we see greed, we can be generous. We can care rather than look the other way because someone else's problems are just too much of a downer. A little “Big I” action will be more helpful than preaching from an ivory tower. A smile will beat a sneer, how much more than a verbal thrashing. Even if it means getting off the couch, sometimes we just have to make the effort so that it's not just about “I,” “Me,” “Mine.” If we succeed more often than we fail, Wonderful! And if we fail just a little too much, there's always, “Better luck next time, kid!”