Like Father like son

Since Sam was a tiny baby we have been told by everyone the uncanny resemblance of BJ and Sam. One of our favorites was when we were in a store when Sam was probably 4 months old and a total stranger came up to BJ and said, "Wow, you sure can tell who's Daddy that baby has, can't you?!" We had no reply. I was sorting through some of our pictures and happened to notice how Sam is now imitating BJ's big cheesy smile in pictures, come on, you know the one. If you don't know it I'll give you an example. Other than Sam's beautiful brown eyes inherited from his birthfather, do you notice the resemblance?

"Mom...I'm taking a shower!"

Wow you can see all the way down to his uvula!

Going on the train at the zoo, SO EXCITING!!!

Now where would he have learned this smile from? Any guesses?