Sorry to disagree with some of you, but we're <i>already</i> past the point where we can expect the resources of the world to satisfactorily sustain us at a decent standard of living.
If we took all the resources of the world and distributed them equally among everyone living, do you have any idea what a shitty standard of living we'd have?
Overpopulation alone isn't the problem, though - it's man's inherent tendencies to favor the good of the individual (himself) over the good of the many that has, and will , lead to our downfall. If this piques your interest at all, I suggest you read <i>The Tragedy of the Commons,"</i> a short essay on our greedy nature. Here's a <A HREF="http://www.constitution.org/cmt/tragcomm.htm">link</A>. Go ahead - it's a good read.
In a nutshell, it states that if a village field (commons) has enough forage to sustain a herd of 20 cattle, and there are 20 families in the village - each with one cow, everyone in the the village will fare well. However, being human, it's only a matter of time before one or more of the villagers realizes that with a second cow, he would be twice as well off, and - even though the good of his village will suffer (because the commons can't support 21 cows - only 20) he'll acquire the second cow anyway - favoring his individual benefit over the losses of the village - even though he is part of the village. This is because the positive aspect of adding another cow to the commons is his alone, while the negative aspect is shared by all 20 families
Now - imagine if the village only had 10 families. Then <i>every</i> family could have 2 cows. Of course, it's only a matter of time before someone would want three . . . . . or four . . .