Carrot or Stick? Group Selection and the Evolution of Reciprocal Preferences

This paper studies the evolution of both characteristics of
reciprocity - the willingness to reward friendly behavior and the
willingness to punish hostile behavior. Firstly, preferences for
rewarding as well as preferences for punishing can survive
evolution provided individuals interact within separated groups.
This holds even with randomly formed groups and even when
individual preferences are unobservable. Secondly, preferences for
rewarding survive only in coexistence with self-interested
preferences. But preferences for punishing tend either to vanish or
to dominate the population entirely. Finally, the evolution of
preferences for rewarding and the evolution of preferences for
punishing influence each other decisively. The existence of
rewarders enhances the evolutionary success of punishers, but
punishers crowd out rewarders.