The summer of 1609 brought two major setbacks that led to the desperate circumstances that eventually led to the Jamestown colonists resorting to cannibalism. First, a fleet of ships bringing 500 settlers from Plymouth and supplies was hit by a hurricane and scattered. Of the new settlers that made it to Jamestown, many were sick and most of the supplies were spoiled or rotten. Second, relations with the Powhatan Indians broke down and they eventually declared war on the colonists. With disease rampantly spreading and certain death waiting for them outside Jamestown, the colonists resorted to eating horses, dogs, cats, rats, mice, and snakes. They also boiled and ate any amount of leather that they could find. Once their food sources were depleted, rather than attempt to gather food from outside the fort (and be killed by the Powhatans), the colonists resorted to cannibalism. For further details, you can read the CNN article that I linked to above.
This actually got me thinking about the popularity of The Walking Dead on AMC. In a world where things become desperate (for instance, zombies coming back from the dead to eat people), many or all of our rules that make us "decent" or "good" people mean little or nothing anymore. The tagline for Season 3 was "fight the dead, fear the living." With limited resources and everyone fearing for their lives, you can't trust anyone to act like "decent people" anymore.
A lot of people like to say that they wouldn't resort to cannibalism, murder, theft, etc no matter what the circumstances. That's a great sentiment, but you can't say that with certainty until you're in a situation where cannibalism, murder, or theft seemed like a viable solution. Of course it's easy not to resort to those things NOW - you have no need to. I'm going to make up three hypothetical situations in which I think people may have a much stronger inclination to resort to what I'll call "end of the world crimes."
The plane you were in crash landed and you were a survivor along with a few others. While attempting to make it back to civilization, weather conditions become severe (rain, snow, etc.) and all of you are malnourished and starving. It comes down to the point where several people have died and others in your group resorted to cannibalism. You declined to eat your fellow group members.
Eventually, your group is able to see a city in the distance and you realize that, given your current levels of strength, the group members who ate other group members are going to make it (barely) to the city but they don't have the strength to bring you along and you know that you won't make it. Another member of the group dies. Do you eat them to stay alive and make it to safety? Keep in mind that hunger, the cold, and malnutrition have driven you very close to insane and your only real instinct at this point is a will to survive. In this situation, you have no other option. You either eat the recently deceased member of your group or you go insane with hunger and then die. Would you become a cannibal?
You survived the end of the world. Nuclear holocaust, zombies, whatever you want to pick as your end of the world situation. You've become the leader of a small group that includes the surviving members of your family and people who have eventually joined up with your group. You know you can trust all of them.
Your group barricades themselves inside a warehouse and is able to get a decent amount of supplies. Things seem to be alright until a group of all men surrounds your warehouse. When you go out to meet them, the leader of your attackers tells you that you can give up your supplies and let them rape all the women in your group and they will move on. Those are their terms. They have superior numbers and firepower.
Your spies later hear the men boasting of the people they had raped and then killed. They're all laughing and bragging about it. Your spies also report that they have a large supply of alcohol and that they get drunk every night and many of them pass out in their tents. Your spies are confident that a small number from your group could easily kill them all during the night. Would you give the order to murder your attackers in their drunken stupor if it meant saving your family and friends?
Your family has fallen on hard times and you live in a poor country. Several of them are ready to die from hunger. You know a way into a wealthy man's food storage and you know that you could get in and out with food without being detected. You know that the wealthy man will still have plenty of food for himself. Would you steal food to save your family from starvation?
Let's change the theft situation. Your family is sick from a disease with only one known cure. You meet another small family that has recently come upon a small supply of the cure but they have the disease as well. You know that you could easily overpower this small family with the help of your siblings and could then cure everyone in your family that has the disease but it would mean letting this small family die from the disease because there wouldn't be enough left for them. The small family consists of a man, his wife, a three-year-old girl and a five-year-old boy. Would you steal the cure?
No matter what you THINK your answer would be to those questions (and I'm interested in knowing how you would answer them, feel free to leave your responses to these hypothetical situations in the comments below)... you can't really know what you would do unless you were faced with those situations. When humanity is at its lowest and most depraved, you may have to do some terrible things to keep your family and friends safe because you know others will do them to you if you don't act first.