The Evolution of Morality

Abstract

A considerable share of the literature on the evolution of human co-
operation considers the question why we have not evolved to play the Nash
equilibrium in prisoners' dilemmas or public goods games. In order to un-
derstand human morality and pro-social behaviour, we suggest it would
actually be more informative to investigate why we have not evolved to
play the subgame perfect Nash equilibrium in sequential games, such as
the ultimatum game and the trust game. The \rationally irrational" be-
havior that can evolve in such games gives a much better match with
actual human behaviour, including elements of morality such as honesty,
responsibility, and sincerity, as well as the more hostile aspects of human
nature, such as anger and vengefulness. The mechanism at work here is
commitment, which does not need population structure, nor does it need
interactions to be repeated. We argue that this shift in focus can not only
help explain why humans have evolved to know wrong from right, but also
why other animals, with similar population structures and similar rates
of repetition, have not evolved similar moral sentiments. The suggestion
that the evolutionary function of morality is to help us commit to oth-
erwise irrational behaviour stems from the work of Robert Frank (1987;
1988), which has played a surprisingly modest role in the scientic debate
to date.

Keywords: Morality, pro-sociality, commitment, ultimatum game, trust game, insurance game, punishment

JEL Classification: C73