“Think of it this way: if you wandered into a cave and saw scratched into the wall some markings which on closer inspection read "Gary woz ere", how would you think that they got there? Would you guess that a river had run through and eroded the wall into a shape? Would you think that perhaps a bear had been sharpening his claws on the rough surface? Or would you be sensible and immediately recognise that someone called Gary, who was probably a bit of a yob, had been through and wanted to leave a message for the world?”