Although diversity has often been proposed to improve group performance, its impact on group cooperation has largely been overlooked. This article uses a theoretical approach to examine the effects of diversity on group tasks in the context of the free-rider problem. We identified 3 kinds of diversity that have been commonly reported to improve a group’s performance: (1) ability, (2) cognitive style, and (3) information sources. Each type of diversity was formalized within an evolutionary simulation based on a foraging metaphor. The simulations were run under different environmental assumptions, covering complexity, costs for cooperation, cue redundancy, and cue compensatory level. Our results indicate that diversity in cognitive style and information sources generally increase cooperation. Both diversity factors also improve group members’ average outcome in non-compensatory environments. However, the outcome results are mixed in compensatory environments. We did not find robust and reliable effects of diversity in ability. Our study provides the first approach to modeling isolated diversity effects on group decision-making in the face of the free-rider problem. It may serve as a theoretical framework for future studies.