The role of cultural group selection in the evolution of human cooperation is hotly debated. It has been argued that group selection is more effective in cultural evolution than in genetic evolution, because some forms of cultural transmission (conformism and/or the tendency to follow a leader) reduce intra-group variation while creating stable cultural variation between groups. This view is supported by some models, while other models lead to contrasting and sometimes opposite conclusions. A consensus view has not yet been achieved, partly because the modelling studies differ in their assumptions on the dynamics of cultural transmission and the mode of group selection. To clarify matters, we created an individual-based model allowing for a systematic comparison of how different social learning rules governing cultural transmission affect the evolution of cooperation in a group-structured population. We consider two modes of group selection (selection by group replacement or by group contagion) and systematically vary the frequency and impact of group-level processes. From our simulations we conclude that the outcome of cultural evolution strongly reflects the interplay of social learning rules and the mode of group selection. For example, conformism hampers or even prevents the evolution of cooperation if group selection acts via contagion; it may facilitate the evolution of cooperation if group selection acts via replacement. In contrast, leader-imitation promotes the evolution of cooperation under a broader range of conditions.
The extension, degree and diversity of cooperation among unrelated individuals are keys to the ecological success of humans. The term ‘cooperation’ refers to behaviours by which benefits arise from the interactions between individuals. Hence cooperative behaviour provides benefits at the group level. From the individual perspective, however, the evolutionary emergence and stability of cooperation are often puzzling. In particular, this holds for social dilemmas where performing a cooperative act is costly to the actor, and free-riding individuals can reap the benefits of cooperation without paying the costs.
In evolutionary biology, which is focused on genetic evolution, the evolutionary emergence and stability of cooperation are the subjects of a considerable body of literature (Axelrod, 1985, Lehmann and Keller, 2006 and Nowak, 2006). Since the dawn of evolutionary theory, Darwin suggested that the evolution of cooperation might be explained by the differential performance of cooperative and non-cooperative groups in intergroup competition (Darwin, 1859 and Darwin, 1871). Ever since then, this idea has been controversial (Leigh, 2010, Maynard Smith, 1964, Queller, 1992 and West et al., 2007a). Evolutionary models demonstrate that selection between groups can indeed favour cooperation, but only under a limited range of demographic conditions (Lehmann and Keller, 2006, Lehmann et al., 2006, Leigh, 1983, Maynard Smith, 1964 and Traulsen and Nowak, 2006). The problem is that within-group processes are typically faster than between-group processes. The rapid spread of individually favoured strategies (like refraining from cooperation) within groups erodes intergroup variation and, as a consequence, undermines the effectiveness of selection at the group level.
