Does Damage Reduction Stack In Pathfinder?

I have not been able to find it stated explicitly anywhere but does damage reduction from different sources stack?

For example I have a Lycanthropic character who has dr10/silver and I was looking at the spell Stoneskin which grants DR10/adamantine. Would these stack or would you simply use the highest one? (So if he was struck with silver you would use the adamantine or if hit with adamantine you would use silver.)