The point of conversations where people just take turns rambling

I'm reading a book now (Gibbard's "Wise Choices, Apt Feelings"), which spends some time talking about what the point of conversation is. His focus is on how language lets us coordinate emotions and actions, where this helps us get along - e.g. you and I will get along much better if I tend to feel guilt when you feel resentful towards me than if I never do.

One thing that the book hasn't discussed (so far), though, is how little people listen to each other in an average conversation. Just from my experience of causally eavesdropping on people, it seems that a whole lot of conversations just involve people taking turns talking, and paying only minimal attention to what the other person's saying.

So what's the (evolutionary) point of such conversations? Here's one guess: we humans walk around with a very complicated set of beliefs about the world, and we do a lot of complicated processing of those beliefs and what we experience. Add to that that we're neurotic, paranoid, and insecure. Because of that, we're dangerously likely to go crazy on our own, and start forming dangerously false beliefs ("nobody likes me," "everyone's out to get me," "I think I've cursed myself," etc.). A good check against that, though, would be to occasionally run our world-view by another person. Moreover, given how complicated our world-representations are, what's best is to be able to communicate lots of that representation at once. And this is what happens in take-turns-talking conversations: people talk and talk, and only really respond to the other person if s/he has said something obviously crazy.

(I think this is something I've mentioned before to a couple people, so sorry for the repeat.)

Also - is the cover illustration of Gibbard's book supposed to be broad brush strokes? That would be funny. If not, I'd like to call dibs.