Why do you sometimes lose bowel function when scared?

Wait -- what's the answer to the question?

Okay, so you might soil yourself when extremely frightened, because in times of extreme stress the body relaxes its control of elimination functions?

That's just rephrasing the question. Why would this be useful to a person (or other animal) when fleeing from or fighting an enemy? If our caveman ancestors with a load in their fur pants always ran slower, they'd have been killed off more often, and nowadays we wouldn't have this interesting reaction.

No conjectures? Maybe it's even just an unavoidable but non-harmful side-effect of *other* changes the body makes that actually are helpful? Seriously, someone somewhere must have put some thought into this.

Cheers!

Some bits make sense...

... like the inhibition of erections. In evolutionary terms it doesn't bode well for running away from attacking cavemen or dinosaurs, either practially or socially.

However it is very effective Darwinism when applied to speed of escape from an angry husband returning to find you doing a bit of 'natural selection' with his wife.

Because, because, because...

"Side-effect of other things" is certainly one answer. The "fight or flight" response starts with a big shot of adrenaline, which puts the sympathetic nervous system into overdrive. This causes bandwidth problems for the central nervous system - no, seriously - and the signalling rate from the internal anal sphincter to the central nervous system drops suddenly, which in turn causes the sphincter to relax.

This mechanism would seem to be a straightforward side-effect.

There's another part to this though; adrenaline has an effect on the external anal sphincter, causing it also to relax and one's bowels to involuntarily evacuate through peristaltic contraction. This latter effect makes me wonder if there could be survival advantages to the response.

Conjecture 1) The sudden evacuation of faeces and the accompanying odour act as a signalling mechanism to nearby members of one's own species that a threat is at hand...

The problem with this idea is that the overwhelming response in mammals to the smell of faeces (particularly of one's own species) is disgust. Soiling yourself when the tiger leaps out of the bushes is more likely to send people downwind of you scurrying off in the opposite direction, not running to help.

Conjecture 2) If you reek of poo, you don't smell like a good potential meal...

Possibly, although mammals - and in particular, carnivores - show a decreased level of disgust response to faeces produced by species other than their own.

Conjecture 3) It makes you lighter and you can therefore run away faster...

This is too silly for words.

I'm going with:

Conjecture 4) Sometimes, sh*t just happens!

Possible reason...

Well, I've got an idea that might hold some, ahem, water.

Say you're one of our simian ancestors in the savannah and you've got a predator running after you. You're legging it for a tree and could use the extra millisecond to grab hold of a branch and hoist yourself to (relative) safety. What to do ? Well, you loosen your bowels and drop a hot and splashy surprise right in the face of your pursuer !

Now, the "pie in the face" effect alone might be enough to send the animal kingdom shrieking with laughter and shame your would be captor back to the lair, but even getting it under its paws might be enough, as the fecal matter is not known for its traction enhancing properties.

Also, once you're on the tree, your scat could be very handy as a projectile weapon against the predator trying to clamber after you. More fun and comical relief !

Maybe this kind of behavior has been documented for chimpanzees ?

What I've been told...

....is that an empty bowel is less likely to lead to infection than a full one in the case of injury.