Fear .  What’s your   biggest fear? Snakes? Planes? Snakes on planes . . . ? Most of us can  think of a couple things that send shivers down the spine. But have you  ever stopped to wonder where  the fear came from initially?   It all starts in the brain.  The same circuit that  jolted humans to fight or flee from a woolly mammoth now gets activated  when you're nervous about a first date.  Long long ago, humans  were probably more in tune to their fear circuits . . . because danger  was a real, immediate thing with a very clear resolution. The whole  process was much simpler—rustling in bushes . . . fear circuit activated  . . . muscles ready. Then, after a quick check of the surroundings, our  cave-dwelling ancestors would have either taken flight, gotten into a  fight, or realised it was just the wind.  If it was the wind, the  fear response immediately dissipated. Fear didn't linger . . . nor did  it leave subtle traces of self-doubt. But somewhere along the timeline,  th...