yet all of these civilized worlds have distinct similarities when it comes to the works and wisdom of the living , namely , the `` befores '' and `` afters '' that define every intelligent world : before and after the harnessing of fire before and after written language before and after the smelting of iron but above and beyond all of these is the single most important milestone of all : before and after a world discovers the ability to lower the number of life-sustaining planets by one .