Parents, personality, hormones, birth order... I'm sure all these play their part.
But I think there's also something about a family's tone (or whatever the proper word would be, maybe culture?).
I grew up in a family that didn't tease. When I got to school I didn't know how to handle it. And we didn't joke enough. Well, my mother rarely told jokes, but the rest of us would. But then we'd go to visit relatives and I'd see an entirely different type of family interaction, lots of teasing and kidding around.
Early in our marriage my husband asked me why I married him. I told him it was because he made me laugh. (Unfortunately, he misunderstood me, and was offended for several months.) When the misundertanding came to light I was able to point out to him that I love to laugh, I like to be happy, I love jokes. I read the funnies every day. Humor and laughter are far more valuable to me than looks or money. No one on this planet can make me laugh faster, or deeper, than he can. And even when he's really grouchy, I can still get him going, sometimes without even having to say anything.
When my boys are teens I hope that we are that family in the dining room, laughing and having fun. We're working hard at it now. We laugh and tickle together. We watch funny movies online. ("Cows with Guns" is a smash hit.) I tell them jokes, even though they don't get them. ("Why did the egg cross the road? Because it had the inclination." Or, "Why did the chest of drawers cross the road? Because it always wanted to be a cross dresser.") They tell me jokes that make no sense at all, then laugh their heads off at them.
Like the title of this post says, "Family differences." We create our own family culture. Some things (like personality and hormones) are out of our control, but some things get set in place early on and become our own family stamp.
=)
Kk..