system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why porn appears disgusting temporarily after masturbating.
gpt
Well, bblinken, the answer is pretty simple: that's a part of something we call the **refractory period**. 

After a man ejaculates, his reproductive system goes into a refractory period. It's like **sex time-out**: No one likes time-out, right? It's okay, though; for some lucky men this time-out only lasts for a few seconds! Some guys, however, aren't so lucky; sometimes it lasts for *hours* or even ***days***.

A long time ago, it was really important that whenever you had sex a baby was made. But, ancient humans *had* to have sex time-out to survive! They had it pretty rough, huh?

Why did they need to have a refractory period to survive? We don't know for *sure*, but we think it has to do with the shape of the penis. It's shaped so that if you keep having sex after ejaculating, it has a chance of scooping out the semen you just put there. If you're an ancient human, that's **bad news**: You can't make babies without semen!

Why is the penis shaped that way? Well, if you want to make sure that you have strong, healthy babies they need strong, healthy parents, right? Imagine that the biggest kid butts to the front of the drinking fountain line after P.E.: He may get to go first, but he doesn't take *all* the water. All the same, the other guys in the group may still get a chance, but all the cold water is gone!

It's kinda like that with our genetic ancestors. The first guy had the best chance to win the sperm-to-egg race, but you couldn't count out the guys who came later if they had penises designed to snatch other guys' sperm right outta there! And that's kinda how the head of a man's penis is shaped when it's erect: like a big scoop.

In short, we evolved a uniquely-shaped penis and an automatic sex time-out to make sure it didn't work against us.