Adapt or die: it's nature's most famous imperative. But how does evolution actually happen? It's too slow to see, but it's going on all around you, all the time. Even if you're on top of the key terms - variation? Natural selection? Parent-offspring conflict? - you still need some context to put them in. From populations to speciation and polymorphism to evolutionary psychology, here's the one-stop source for all you need to know.