Back in the 60's a lot of people were talking about global overpopulation. Recently this doesn't seem to be much of an issue any more, but shouldn't we worry about this? Isn't there a limit to the number of people our planet can sustain?
Some figures on world population:
http://www.census.gov/ipc/www/img/worldpop.gif
http://www.census.gov/ipc/www/img/worldgr.gif
In some way we, humans, are in a very strange position. Never before has an animal so completely outcompeted it's natural enemies. As a result of this position there's is no natural limit to our population growth. So without any intervention, our population would keep growing beyond the capacity of the earth.