Humor-Related to Clueless R C-less they're C-less thread

I conducted, I will admit, a severly flawed experiment on a know clueless person of my aquaintance.

The findings being that this person was indeed clueless.
It was still fun

This same person has years exhibited a total lack of understanding humor.

Clueless will laugh at jokes, but really doesn't "get" them. The same for when someone is just telling an amusing story.
If someone says, "And then she had to run out of the house naked!" and everyone laughes, Clueless will too, but will say something like, "yeah, her house is really nice"

Also, C-less just takes the cue to laugh because others are. If you're alone with her and say something funny, her answer may be, "yeah, I bought shoes there once"

This has been noticed by a lot of people, so it's not just me.....

Anyway - What do you think it is that causes some people to have an acute sense of humor, and others next to none?

I don't think it's always related to being clueless, or not
I seen this with both intelligent and not so intelligent people.

Maybe it has something to do with some people only able to take things literally?

Thoughts?