though I have yet to hear of animals making sex videos in the wild

LoL :D - so you gave yourself the answer, there is no prostitution going on in the animal kingdom. Or, I have a completely different understanding of the term prostitution.

If this behavior persists in animal populations, then it must have an evolutionary advantage

A very daring statement, I'd say. Would not sign it.
Watching an act of coupling because you happen to come across it (for example, a couple having a sweet secret rendezvous in the woods) or going to a whore and paying for it are two completely different things. I am unable to put a link to human evolution on that.

I find porn abysmally disgusting as a trade, but not purely random or spontaneous sex performance between male and female; which is not porn but them simply having sex. There only needs to be a certain erotic tension and not even the act itself in its entirety to make my heart beat faster. I bet you are the same ;)

Because modern people seem to take fewer opportunities to make such random observations (or be the ones observed) doesn't mean that porn is a good choice. It is not for me. You wouldn't want your wife/girlfriend, your daughter or even mum to be getting it on, would you? Or who prostitutes herself online?

Since porn is also a matter of fact, I will not give it my credit. It needs to stay in the dirty corner, since it won't go away. I think that is realistic but I am not making myself an advocate for it.