No formal theories have been composed as of yet. We can compile a couple of basic ideas in psychology and apply them in this particular behavior.
For instance, you could theorize that gossiping is a maladaptive behavior tied to a desire for social contact\interaction. We know that all humans crave some form of social contact (except for schizoid personality disorder sufferers). We also understand that most behaviors are genetically based or learned (Developmental\Behavioral Psychology theories). So, we can hypothesize -under these conditions- that the process of spreading rumors is a way of influencing those around us for the primary purpose of getting attention. Its a maladaptive behavior in the sense that gaining attention this way is harmful to others, and because it is not supported by the population as a whole.
I'm kinda taking a shot in the dark, but tell me if this is kinda what you are looking for.
