You have to run it and pass it. The reason for the evolution of the quarterback position is defensive speed. Teams have become so fast on defense that it's imperative for a quarterback to be able to move not only inside the pocket, but also outside it. The speed along the front seven has increased significantly in the past decade. That's what everybody wants on defense.
Defensive ends are lighter and faster, while linebackers seem to be getting smaller and quicker.
That, in turn, has forced offenses to come up with mobile quarterbacks, guys capable of putting pressure on fast defenses. Last season, Donovan McNabb led the Philadelphia Eagles to the NFC Divisional Playoffs. The second-year quarterback played so well some were calling him the MVP of the league. He did much of his damage outside the pocket. Not only was McNabb a threat to run the ball, he used his feet to escape pressure and make plays with his arm.