After Earth is a science fiction adventure film about a man (Will Smith) and his son (Jaden Smith) who are trapped on the deadliest planet of all: Earth. That is, Smith and Smith are on Earth of the 31st century, over a thousand years after the planet kicked us off. Since then, the animals left behind have become more ferocious, and our protagonists have to find a way off before they become animal chow. But as with many Hollywood projects, the story had evolved even faster than Earth's latter-day fauna. It turns out the sci-fi story was originally … something else.

We spoke with screenwriter Gary Whitta over the phone, who explained that, although he wrote the screenplay (along with M. Night Shyamalan), the story originated with Will Smith.

"Will always wanted to tell a kind of father and son bonding story. In fact, it wasn’t a science fiction movie originally to begin with. It was set modern day, and Will and Jaden were military father and son who were on a trip to Alaska."

We can see the origins of that initial idea in clips like this one, where Jaden has to fend off simian assailants. Just swap out "stranded on an abandoned planet with aggressive monkey creatures" with "stranded in the wilderness without cell-phone coverage and a hungry pack of wolves."

But the original idea was embellished "once he hit upon the idea of doing a big science fiction movie one thousand years into the future."

So how did Whitta become involved in this adventure? Smith knew Whitta from his work as a screenwriter of another post-apocalyptic movie, The Book of Eli. "[Smith] brought me on as someone as kind of a science fiction geek to help him build that world."

That included "what the makeup of this society would look like. Will and Jaden are speaking in kind of polyglot accent. They worked with a dialect coach to come up with an original accent, because the idea of the characters speaking with an American accent or a British accent one thousand years in the future, after you’ve left Earth would seem kind of preposterous.

"There’s actually different versions of the accent based on your position in society. So there is people lower down in the social order have kind of a working-class, a more guttural version of the accent. And Will’s character in the movie is of a higher order; an almost aristocratic level of society has a more refined version of the accent. So there is a tremendous detail that went into that."

After Earth opens today. No aggressive monkey creatures were harmed in the making of this movie.