Random Musing.

Does a smile, in it's most generic form, transcend the boundary of every single culture? Is it a universally recognizable expression of joy?

(This may seem like a "duh" question, from Captain Obvious, but I find it hugely important in relation to cultural - and maybe, in a tiny way, moral - relativism.)

Has the smile permeated all cultures, no matter how isolated they are from one another? If so, why?