I should note that it is quite possible to acknowledge the role of evolution in our development without assuming that all traits have to be advantageous to the organism in order to become widespread. The phenotypic traits we recognize, classify as traits and talk about (like a sense of humor) are not the same as the genotypic traits which are passed down from parent to child. It is possible that a trait is so closely linked chemically to a different and advantageous trait, that it survives without being beneficial itself. So, for instance, it is possible that the sense of humor is a by-product of the development in the brain for the ability to move our arms; the production of the proper hormonal bath to cause one to develop also causes the other.
But I don't think that this is the case.