"It's just another way of recording an actor's performance," said Serkis.
In the film, Caesar is used as a test subject for a new Alzheimer's drug, only the drug gives him unexpected intelligence.
"He's brought up by humans," said Serkis. "He has a moment of self-awareness where he realizes he's kind of a freak and he doesn't know what he is- whether he's an ape or a human."
And it's all in modern day San Francisco.
"He's literally thrown into a sanctuary with other apes where he doesn't relate to, who he's alienated by," said Serkis. "And then eventually, he leads them to revolution."
Serkis says this form of acting is all in the imagination.
"You don't have any help from costume or make-up," said Serkis. "And so what it does, what it does brilliantly, is it helps actors to just play off each other."
"Rise of the Planet of the Apes" opens Aug. 5.