Jerry Coyne wrote an interesting article about the evolution of laughter. He closes with ..
So laughter, at least when being tickled, appears to be an evolved, innate phenomenon. As I emphasized above, this says nothing about whether it was selected for directly, whether it was a byproduct of something else that was selected, or is simply a nonadaptive epiphenomenon. But as I write, evolutionary psychologists are working on why evolution may have promoted laughter.Of course evolutionary psychologists are busy working on an adaptive just-so story. That's what they do. You won't catch them explaining anything as an accident or an epiphenomenon.