The Evolutionary Benefit of Laughing

What is laughter itself doing for us? There's definitely one element of it, which is being able to find a way not just of experiencing surprise but also of dealing with difficult situations by staring them in the face. What would be the evolutionary advantage of having this particular thing? And again, I don't think anybody really can say with any confidence what that might be. Next week, it's the healing power of pets with Dr. Art Markman and Dr. Bob Duke.