Here is how you know someone has had a good idea: Other people freely admit to their friends that said idea has changed their lives. Most people today will grant that fire and the wheel are the big two. After that, any attempts to rank the greatest ideas of all time are going to draw lots of argument. You’ll have zealots pimping this god or that on the one hand, scientists pimping Darwin on the other, and then practical people pointing at written language and saying, look, fellas, the reason those ideas have gone viral is because someone figured out how to write them down.