One of my favorite cartoons is Peabody's Improbably History. It was part of the excellent Rocky and Bullwinkle series, so it's no surprise at how much fun it is. There was an "origin" episode where it was explained, all in about 2 minutes. Since I'm watching the Mr Peabody and Sherman movie now, I wanted to see an episode of the original series.
I love how no one even questions why Peabody is a talking dog, much less a genius. Hopefully this movie will be the same way. I'm sure there will be more to it than that, as most of these adaptions need to explain things.