As the morbid and jaded creatures we are, humans really get a kick out of pondering our species' ultimate demise. We have the usual cast of suspects--an infectious pandemic, climate change, meteor collision and nuclear war. Ok ok, I'll throw alien invasion in there too. But it's high time we give some love to some more obscure, but still scientifically plausible means of extinction. I mean why limit ourselves, really?
So here are four under-represented threats to human existence we can all happily ponder.