Came across this video of comedian Louis CK on Letterman, where he argues that we should add lions as selection pressure on human beings. In his words:   
“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…”
It's an interesting point overall, though. We are increasingly changing our environments, and, in doing so, also the selective pressures that act upon us.