All this week, we've been talking with our friends from Scientific American about endings — how cultures fade, and natural resources dwindle. Today, we’re focusing on something even bigger: the end of human life as we know it — in other words, the apocalypse. The question of course, is how will it happen? Nuclear war? a killer virus, or perhaps an environmental disaster?

The New England Journal of Medicine has printed the story of an ethical dilemma that doctors at Massachusetts General Hospital grappled with back in 2008. Is it ethical to keep a brain-dead patient on life support to harvest her eggs, in the hopes of allowing her husband to still father her child?