Is a person born with a sense of humor or is it learned?

My 7 year old grandson is a very serious kind of kid. He’s really smart too. He’s into astronomy pretty big.
My daughter started playing a verbal game with him involving the twins (3 months old.) One day, while working in the kitchen, she said, “Aden! Did you put those babies on my floor?”
At first he was non-plussed, and gave a serious answer. “No. You did, about 5 minutes ago.” Looking at her strangely.
But she’s carried it on for about the last week, dropping hints of what some possible answers could be, and he’s gotten into the spirit of the game, making up scenarios of where those two babies came from, and it gets more imaginative and interesting as time goes on. “I found them at the park and brought them home for you. I thought you would like them.”
Mom says, “And I DO like them! Very much!”
This morning she said, “Aden. Did you put those two babies in my bed last night?”
“No, Mom. The baby fairy put them in your bed. You were so good she decided to give you TWO!”

He needs that. Like any kid, he’s got a great imagination, but in his case it doesn’t tend to lean toward the impossible kinds of things. You’ll catch him driving and humming on the couch, making rocket bangs and crashes, and ask him where he’s going. He’ll say, “Well, I’m going to Mars because I could live there because they found ice there!.... But…no. It doesn’t have the right atmosphere so I couldn’t.” Then he’ll be bummed out for 5 minutes. Then he’ll cheer up and say, “Wait! I can bring some plants to make the right atmosphere!” Resume journey, only he’s taking Gramma with him now, and she asks a LOT of questions! ;)

I just think this new game his mom started is deliberate awesomeness for a serious kid like that!