Are great actors and actresses usually more intelligent than people with average jobs?

It seems that having a strong imagination and being able to convey that imagination in body movements and voice is very hard to achieve for me. It may be that I just haven't done a form of acting for very long at all. Is it a talent that God has to give you to be able to act like one of the greats? Is it time spent doing it over and over? Or does great acting hinge upon a higher level of intelligence?