Sexual Selection of Co-operation
M. Afzal Upal
upal@iet.com
Simulations of iterated prisoner's dilemma games have
been widely used in social sciences to study the evolution of co-operative
behavior. Axelrod's (1994) pioneering work showed that seemingly co-operative
strategies such as Tit-forTat (TFT) can do better than selfish strategies
such as always defect in a wide range of environments. TFT strategists
start out co-operating and then do what the other player did on the previous
move. Further work by Axelrod and Hamilton (1987) suggested that co-operative
strategies such as TFT can automatically arise in a population of individuals
through evolution. However, subsequent work has shown that neither TFT, nor
any other pure or mixed strategy, is evolutionarily stable. This has lead
researchers to consider other factors that can enhance the evolution of co-operative
behavior. Sexual selection is one such mechanism (Miller 2000).
In this paper we report on the results of the simulations that we performed
to test the hypothesis that female preference for mating with co-operating
males can enhance the evolution of co-operative behavior among males.
The model involved building a heterosexual population
of 100 agents. The sex of an agent was randomly chosen to be male or
female. Game playing strategies of the first generation of agents
were also randomly chosen. Two players were randomly chosen to play
R rounds of prisonerís dilemma game. After the game playing
rounds, players of opposite sex were allowed to mate and reproduce
children. Strategies of the children were produced by "crossing over"
the strategies of their parents. The only difference between a male
and female agent modeled was the cost of reproduction. We ran experiments
with various values of male and female cost of reproduction and with two
mate selection
strategies; random and preference for the most co-operative male. The
evaluation metric was the difference in the emergent strategies of 100th
generation. Our preliminary results show that under a wide variety
of
conditions, sexual selection does indeed lead to significantly higher proportions
of co-operative strategies.