A funny piece from Louis CK on the Letterman Show! He brings up some very good point about human evolution:
"I think human beings are still evolving and we're all responsible for that. There's nothing less than the human evolution at stake when you act like an idiot. And If you are idiot then you should be selected out. Not by a committee, but by lions..."
Through humor though he brings up an interesting point that how would we behave if we lived in fear of lions? According to Louis CK we would "have to be smarter and more interesting. You couldn't just be a fat pig at Carls Jr just pigging out cause a lion might eat you!"
Perhaps the greatest selective force on humans is humans. We created our own ecosystems to the point where we can live rather comfortably without fear of lions, or more metaphorically any non-human phenomenon, attacking us at every corner. The lions we face now are ourselves.