Jump!

Have you ever stood on the edge of a high steep drop and felt the urge to jump off? People talk about it all the while. What's the point of that then? Having a sudden desire to jump off a precipice doesn't sound like a very good evolutionary adaptation?

Admittedly everyone mentions this, but no-one ever actually does it. I wonder if it's a trait inherited from a brachiating ancestor? Let's look at what actually happens when you're peering over the edge of the Forth Bridge, or hanging onto a very high tree. We have a very strong drive for self-preservation that tends to warn us when we're on the edge of a dangerous drop. But if you're a tree-swinging ape that's a bit of a hindrance. You'd never get anywhere if you were too scared to move.

So what's the answer? You can momentarily suppress the self-preservation mechanism, but that's pretty dangerous. What happens when you swing across and land on a tree with a resident snake and your instinct for caution is dampened? OK, so if suppression isn't the answer, how about another instinct that is far stronger and temporarily overrides the need for caution?

In order for that to work you've got to have some kind of very quick reward system, otherwise how are you going to get your brachiating ape to leave his lofty perch and leap into the unknown?

This would appear to be a good system then - while you're hanging onto a swinging tree-trunk, you see another branch within reach. You get a sudden rush of adrenalin, and a voice in your head yells "Jump!". You leap across, successfully grab the branch, and you're rewarded with a nice tasty endorphin rush.

This explains the contradiction between the feeling of caution and the anticipatory desire to jump that we get on the edge of a precipice. There's no branch there to leap to, but the ancient mechanism still kicks in from time to time. Also neatly explains the buzz that sky-divers get, and why they keep doing it.