Puzzle 12 is the killer - most people need help to find it - the villagers won't find it on their own. Take a look at the first (or maybe second) post in this forum as to how to get hints.

There's really not much point in trying to keep the population down - after all, the GC has to come from somewhere and no babies = no GC.

Good Luck with the Hard level - I've gone back to easy and I'm experimenting (unintentionally) with how many ways I can kill off an entire village in the shortest possible time!