AlterNet: AMCs The Walking Dead is at the top of the cultural zeitgeist these days, one of the most popular television series on the air. In the show, a virus has ravaged the Earth, killing most of humanity, with the dead corpses rising to terrorize the few remaining living souls. While enormously entertaining, it is not a likely scenario for the end of the human race. Dick Cheney notwithstanding, zombies arent real. The end of humanity, however, could be. While it is difficult to envision a world without...