Paul Bloom at Small Potatoes:
Why do we enjoy showing and sharing?
Showing first. A certain sort of evolutionary psychologist (like me, on some days) would point out that, when properly done, showing impresses others. It’s similar to making people laugh or surprising them with a sharp observation. Maybe we enjoy showing, then, because it raises our status. It makes us more desirable as a friend, partner, or lover.
A different, but compatible, explanation applies to both showing and sharing. It involves empathy, and like many clever thoughts about empathy, it comes from Adam Smith.
More here.