I say it is the Squirrel Revolution that does humanity in. They're always stockpiling food. But for what? It's as if they're preparing for something... 

I say it is the Squirrel Revolution that does humanity in. They're always stockpiling food. But for what? It's as if they're preparing for something...![]()
There are three or four ways it could happen:
5) Mystery Virus/Zombie Scenario - This is the one no one really thinks can happen, but is no less likely then the others.
Actually, it's far less likely than any of the other possibilities you laid out, at least as far as the zombie part of it goes. Everything else on your list has happened before, and is likely to happen again at some point. However, while a mystery virus moving fast and wiping out the Earth's population is plausible (The bubonic plague, etc.), to date, we have not discovered a way to make the dead walk, or turn people into mindless brain hungry cannibals.
Actually, it's far less likely than any of the other possibilities you laid out, at least as far as the zombie part of it goes. Everything else on your list has happened before, and is likely to happen again at some point. However, while a mystery virus moving fast and wiping out the Earth's population is plausible (The bubonic plague, etc.), to date, we have not discovered a way to make the dead walk, or turn people into mindless brain hungry cannibals.