  Using methods from evolutionary game theory, this paper investigates the
difference between social cohesion and task cohesion in promoting the evolution
of cooperation in group interactions. Players engage in public goods games and
are allowed to leave their groups if too many defections occur. Both social
cohesion and task cohesion may prevent players from leaving. While a higher
level of social cohesion increases a player's tolerance towards defections,
task cohesion is associated with her group performance in the past. With a
higher level of task cohesion, it is more likely that a dissatisfied player
will refer to the history and remains in her group if she was satisfied in the
past. Our results reveal that social cohesion is detrimental to the evolution
of cooperation while task cohesion facilitates it. This is because social
cohesion hinders the conditional dissociation mechanism but task cohesion
improves the robustness of cooperative groups which are usually vulnerable to
mistakes. We also discuss other potential aspects of cohesion and how they can
be investigated through our modelling. Overall, our analysis provides novel
insights into the relationship between group cohesion and group performance
through studying the group dynamics and suggests further application of
evolutionary game theory in this area.
