Evolution - Holding It

The other day, I was going back home after a lunch in a restaurant. I had drunk a lot of water and a large beer, and didn't go to the toilet before leaving. Through the drive back, the urge to pee was rising, and I analyzed what was happening to me. I noticed four distinct phases, but they are very hard to describe, and out of scope. (Easier to describe was that, in the third phase, heat rushed to my head.)

Describing the urinary system is also out of scope. What this post is about is that the experience led me to wonder why, in an evolutionary point of view, we have the ability to "hold it in". After all, in nature, what difference would it make to pee uncontrollably where we stand?

It took me a couple minutes to find out the most likely reason. Urine is used to mark territory, but also gives position. A prey hiding from a predator would easily be found if his system decided to release.

Also, an animal peeing in its den (for example), would give its den's position (and its babies) as surely as a flashing red light at the entrance.

Over millions of years, a sphincter was slowly formed to stop the flow, until voluntarily released. Those with a stronger sphincter had a bit less chance to be found, and through natural selection, we have a sphincter today.

An interesting thing to know would be if the sphincter can be exercised to be stronger.